Micrococcus luteus Isolated From a Fish Tank Filter

Ariana Casey

BIOL 342 — Microbiology


The human race predominantly lives on land and breathes in the air surrounding them, not giving much thought to the bodies of water that cover the majority of the earth’s surface.   In all these environments exists a common organism — bacteria.   One must look past the human —past what the naked eye can see- to understand the bacteria.   Many species exist, inhabiting a multitude of niches in the world, from the inside of soil clumps and the bottom of the ocean —devoid of oxygen- to the skin on our hands and the surfaces of plants —with aerobic respiration to sustain them.

With so many different species of microorganisms, it would be a shame to disregard the ones that live in water simply because it’s not the environment that people exist in.   With the human body and the surrounding environment being so dependent on water, is would make sense to examine this substance to find what microbes exist there.   Among one of the many uses for water that people have, the one that seemed it would have a good measure of microbiota was a fish tank filter.

The objective of the following research was to isolate a bacteria from a sampled location and to determine through physiological and genetic testing what bacteria was isolated from the sampling location.  Being that a fish tank seems a rich environment for microbiota, it is hypothesized that the bacteria will be unique, with the ability to live aerobically or anaerobically.



The chosen location for sampling was the filter of a fish tank.   To properly sample, the filter was first removed from the water.   After removal from the fish tank, the filter was swabbed with a cotton swab, which was then streaked over the surface of the TSA plate (Lab Handout 1).   The plate was kept at room temperature for six days before being brought into lab.   At this point, a colony was pulled with a sterilized metal loop and put onto another TSA plate using a quad streak (Lab Handout 2).   As the bacteria grew, individual colonies were used to further isolate the bacteria through additional quad streaks.

At the fourth quad streak, the culture was determined to be fairly pure through microscopic observation (Lab Handout 4).  At this time, the culture was deemed pure enough to be physiologically and genetically tested to determine bacterial strain.


One objective of obtaining a pure culture through quad streaking was to observe the colony morphology of the cells in isolate (Lab Handout 2).  To determine cell size, shape, arrangement, and wall-type, gram-staining was performed (Lab Handout 4).     Fluid thioglycollate test was performed and incubated at room temperature to determine oxygen class (Lab Handout 6).   Presence of cytochrome C oxidase was tested using an oxidase test strip with an indicator dye (Lab Handout 6).   A catalase test was used to determine if the strain of bacteria has the enzyme catalase (Lab Handout 6).   To determine which sugars the bacteria could ferment, as well as to determine other physiological characteristics which could help to characterize the isolated bacteria, an API 20E test strip was used (Lab Handout 6).   Later, due to the results with API 20E being semi-inconclusive, and with more information on the isolated bacteria, the API staph strip was used to test the bacteria.

To determine if the isolated bacteria had the ability to grow in the presence of methylene blue, and further to see if it could ferment lactose and/or sucrose, the isolate was plated onto Eosin Methylene Blue (EMB), following lab 6 protocol.   For determining if the isolate had the ability to grow in the presence of crystal violet and bile salts, and to further determine capability to ferment lactose, the isolate was plated on MacConkey (MAC) Agar (Lab Handout 6).

Additionally, to further determine the identity of the isolated bacteria, its susceptibility or resistance to various antibiotics was tested via the protocol of Lab Handout 9.  The isolated bacteria was suspended in TSB and then plated with a cotton swab onto two TSA plates, onto which antibiotic discs were placed evenly apart.  To determine susceptibility to antibiotics, zone diameter was measured once a bacterial lawn had time to form (approximately 48 hours past inoculation).  The tested antibiotics were Amakicin, Cefaperazone, Vancomycin, Trimethoprim, Oxacillin, Clindamycine, Piperacillin, and Gentamicin.


An isolated pure culture bacteria colony was suspended into tryptic soy broth (TSB).   After a week, this TSB suspension of bacteria was used for genomic DNA extraction (Lab Handout 5).     DNA extraction was done using the PowerSoil DNA kit (MoBio), which was sequenced using Illumina MiSeq technology at the University of Alaska Fairbanks’s DNA Core Lab (Lab Handout 5).   The data procured from the Illumina Miseq sequence analysis will then be computed using BaseSpace (Lab Handout 7).  Assembly of the genome was done using the SPAdes Genome Assembler application (Lab Handout 7).  Using the Kraken Metagenomics application and the assembled genome, a taxonomic classification of the bacterial isolate was determined (Lab Handout 7).  The final application used on the data procured from the DNA Core Lab sequencing was the Prokka Genome Annotation to determine potential functional genes of the genes (Lab Handout 7).

To further analyze the results, the first node of the contigs.fasta file was pulled from the SPAdes Genome Assembly application and ran through the Nucleotide BLAST (Basic Local Alignment Search Tool) application provided by the U.S. National Library of Medicine.



The pure, isolated bacteria grew in yellow-pigmented, shiny, smooth, small, and roung colonies.  Gram-staining revealed the bacteria to Gram-positive in nature, with cocci approximately 1.5 um in diameter.  The cells were usually found in tetrads with the smallest aggregations being diplococci, though often the cells would clump further.   The fluid thioglycollate test determined the bacteria to be an obligate aerobe.   Hydrogen peroxide resulted in formation of bubbles, testing positive on the catalase test.   The oxidase test strip turned a light grey-purple in the presence of the bacterial suspension, testing positive on the oxidase test.   The API 20E tests came back predominantly negative, with the only reliable positive being the test for presence of gelatinase.   Additionally, the VP turned a slight pink within the 10 minutes after VP1 and VP2 reagents were both added.  This was inconclusive as to whether the test was positive or negative.  With the API Staph strip, there were also all negatives within 48 hours of starting the strip.   After addition of the VP and NIT reagents (there was no access to PAL reagents, so that test is inconclusive), the VP turned slight pink after the 10 minutes.  Using apiweb as a resource, I determined this to be a positive reaction.

Antibiotic testing results (Table 1) reveal this isolate to be fairly susceptible to antibiotics.

Table 1: Antibiotic Zone Diameters and Susceptibility
Antibiotic Zone Diameter (mm) Susceptible, Intermediate, or Resistant
Amakicin *radius: 22 Susceptible
Cefaperazone *radius: 18 Susceptible
Vancomycin 29 Susceptible
Trimethoprim 15 Intermediate
Oxacillin 15** Resistant**
Clindamycine 36 Susceptible
Piperacillin 50 Susceptible
Gentamicin 36 Susceptible
*Radius was used where the zones overlapped and the diameter was impossible to measure due to overlap.  The radius of each zone was greater than the determined diameter susceptibility range.

**Plated oxacillin disc was contaminated with a piece of agar from another lab mate’s bacterial isolate, and so would be inconclusive, but my bacterial isolate was used by another student that lost their isolate in a lab clean-up.  This student also used the Oxacillin disc and had a zone diameter in the resistance range.



Basespace results indicate that the bacteria is likely Micrococcus luteus NCTC 2655 with 75.83% of the reads classified and 98.59% of the 73.91% analyzed reads were classified to the species level.   This is further supported by the BLAST results, which indicated a 97% identity match to Micrococcus luteus NCTC 2665.   The SPAdes Genome Assembler data revealed a genomic length of 2,615,526 base pairs with a GC content of 72.41%.   The bacteria also had 53 tRNAs and 2365 coding regions.   Probable functional genes were discovered through use of the Prokka Genome Annotation application.  Putative acetyl Co-A acetyltransferase, putative oxidoreductase, and NADH dehydrogenase-like protein SA0941 were all probable functional genes found in the genome of the isolate.


The bacteria isolated from the fish tank filter was not a unique microbe, as was expected, but a ubiquitous microbe found in many niches.  Additionally, the bacteria was surprisingly an obligate aerobe, which was unexpected as with an environment comprised mainly of water.  The ability of the bacteria to survive in such an environment may be due to the ability of M. luteus to become quite dormant and awaken with the use of the Rpf gene (Mukamolova et al 2002; Young et al 2010).

Identification of the bacterial isolate through the genetic data alone is alright in cases where the said bacteria cannot be plated and isolated.  In the case of this study, looking at both the physiological and genetic aspects of the bacteria for being able to identify the bacteria as Micrococcus luteus NCTC 2665 strain is important.


Micrococcus luteus NCTC 2665 “Fleming Strain’ have a distinct yellow-pigmentation to them, likely an adaptation to protect against radiation (Young et al 2010).  The bacteria is quite ubiquitous, in that it is usually found on mammalian skin, but can also be found in soil as well as fresh and marine water (Akayli et al 2016; Rickard et al 2002; Young et al 2010).  This aligns well with the sampling location being a fish tank filter, as the bacteria are found in water, plus the filter is something often handled by people, thus either could have been the source of the M. luteus at this particular location.  The bacteria is known to be coccoid, gram-positive, and form mainly tetrads (Akayli et al 2016).  With the tetrads, clumping happens, which makes sense as M. luteus are observed to create coaggregates in fresh water with some other bacteria to form a biofilm (Rickard et al 2002).  Additionally, M. luteus tests positive for both catalase and oxidase, all of which agrees with the testing done for the isolated bacteria.

The result of being an obligate aerobe from the fluid thioglycollate test also falls in line with the literature on M. luteus (Young et al 2010).  The physical test results of the API Staph test, when placed into the apiweb resource, come back with a 99.1% identity as a Micrococcus species, with an oxidase positive and yellow colony morphology leaning the test results towards Micrococcus luteus.


With both the BaseSpace and BLAST results identifying the strain as M. luteus, especially with all the physiological evidence, it would be hard to refute that the isolated strain is, in fact, M. luteus NCTC 2665.  Beyond this, additional genetic evidence points to the identification of the strain obtained as M. luteus.  For one, the GC content of the isolated strain was 72.41%, while it is 73% for NCTC 2665 (Young et al 2010).  Strain NCTC 2665 has 2,501,097 bp, encodes 2,403 (of 2,458 total) genes to proteins, and has 48 tRNAs, which is all comparable to the isolated bacteria’s 2,615,526 bp, 2,365 coding genes, and 53tRNAs (Young et al 2010).  Of the genes, the oxidoreductase, CoA, and NADH-like protein mentioned beforehand are all important to M. luteus.  Cytochrome c oxidoreductase is a component of the respiratory chain and CoA is part of the citric acid cycle (Young et al 2010).

In discussing genes, it is important to relate some of them to physiological aspects that are seen.  A lack of glucokinase, for instance, results in M. luteus being unable to grow with glucose alone as a carbon source, which is what we witnessed through the API test strips having negative results for fermentation of glucose (Young et al 2010).  Additionally, the high susceptibility of M. luteus to antibiotics is possibly due to lack of the gene wblC, as it is a pleiotropic regulator in other bacteria that helps with resistance towards antibiotics (Young et al 2010).

Additional Discussion

The strain represented in this research is the “Fleming strain’ NCTC 2665, which is still known as Micrococcus luteus, but another strain of M. luteus —primarily ATCC 9341- has been reclassified as Kocuria rhizophila (Tang and Gillevet 2003).  In fact, the NCTC 2665 strain had, “recently’ (in accordance to a 2010 paper) been declared taxonomically separate from K. rhizophila (Young et al 2010).

Strain ATCC 9341 is different in a few ways, some being that it is oxidase negative compared to the oxidase positive nature of NCTC 2665, as well as that the strain ATCC 9431 forms acids from glucose and fructose, neither of which were positive tests on the API test strips performed, meaning that my bacteria isolate does not confer with the traits presented by the Micrococcus luteus ATCC 9431 strain that was reclassified as Kocuria rhizophila (Tang and Gillevet 2003).  It, indeed, appears that the isolated bacteria follows more closely with the “Fleming strain’ NCTC 2655 of M. luteus which has not been reclassified to Kocuria rhizophila.



Akayli, T., Albayrak, G., Ürkü, Ç, Çanak, Ö, & Yörük, E. (2015). Characterization of Micrococcus luteus and Bacillus marisflavi Recovered from Common Dentex (Dentex dentex) Larviculture System. Mediterranean Marine Science, 17(1). doi:10.12681/mms.1322

Mukamolova, G. V., Turapov, O. A., Young, D. I., Kaprelyants, A. S., Kell, D. B., & Young, M. (2002). A family of autocrine growth factors in Mycobacterium tuberculosis. Molecular Microbiology, 46(3), 623-635. doi:10.1046/j.1365-2958.2002.03184.x

Rickard, A., McBain, A., Ledder, R., Handley, P., & Gilbert, P. (2003). Coaggregation between freshwater bacteria within biofilm and planktonic communities. FEMS Microbiology Letters, 220(1), 133. doi:10.1016/S0378-1097(03)00094-6

Tang, J. S. and Gillevet, P. M. (2003). Reclassification of ATCC 9341 from Micrococcus luteus to Kocuria rhizophila. International Journal Of Systematic And Evolutionary Microbiology, 53(4), 995-997. doi:10.1099/ijs.0.02372-0

Young, M., Artsatbanov, V., Beller, H. R., Chandra, G., Chater, K. F., Dover, L. G., . . . Greenblatt, C. L. (2009). Genome Sequence of the Fleming Strain of Micrococcus luteus, a Simple Free-Living Actinobacterium. Journal of Bacteriology, 192(3), 841-860. doi:10.1128/jb.01254-09

Micrococcus luteus

Bailey Carter

Microbiology F342x Lab F01

Dr. Leigh

28 April, 2017

Micrococcus luteus

Intro: Microbes are everywhere, even in the most extreme environments and conditions. They can be found in boiling hot springs; they can be found in frigid waters in the artic. They can even survive in conditions that have very little of even no oxygen, using glycolysis and alternative electron acceptors to create ATP. With this almost universal range of survivable living conditions that microbes can live in (particularly bacteria), it would be reasonable to assume that there would be at least one variety living in such a nice, wet, and aerated place as my shower drain. Therefore I used this as my location to take my environmental sample from. I would hypothesise that because we clean our shower regularly, that most of the bacterium un the shower drain would come from people in my family taking a shower, and mostly be from the skin. Organisms commonly found on the body include Micrococcus, Staphylococcus, and Corynebacterium species (Dermnet New Zeland). These residential skin organisms are also fairly ubiquitous in the environment. We were aiming to isolate a bacterium from this initial environmental sample by using repeated quadrant streaks to isolate single species colonies, therefore producing a pure culture that we could do a multitude of tests on which include Gram staining, genetic analysis and antibiotic testing along with many other tests. Based on the place of origin of the bacterium that I isolated, I hypothesize that it will either be one of the above bacterium or a similar water loving organism, likely one that also forms a biofilm. I also hypothesize that it will be an aerobic organism, given that I found it in a well aerated environment and it has survived until I cultured it. When looking back after culturing the isolate, these hypothesies were supported by several of the tests, and served as a good tool to steer me towards what the isolate may be.

Methods: To start isolating the bacterium, I used a sterile swab wet with deionized water provided by the lab to pick up bacteria from the shower drain. I then streaked the exposed swab onto a petri dish to allow the organisms to grow, incubating them at 25 degrees Celsius in a dark cabinet. Then to actually isolate a bacterium, I chose a colony from the initial plate and did a quadrant streak of it to further isolate the bacterium, and then incubated it at 38 degrees Celsius for a week. I then repeated this three more times to further purify the isolate. I then transferred the pure culture into a TSB slant to preserve it, keeping it at around 3 degrees Celsius in the lab refrigerator.  To identify our isolate after obtaining the pure culture, we performed many different tests. I performed a Gram stain test to identify if the bacterium was gram negative or positive, as described in the Lab 4 handout. Another test I did to identify my isolate was DNA analysis, described in lab handouts 5 and 7. I isolated the DNA by lysing the cell and using the Power Sol DNA Isolation Kit to isolate the DNA from the other parts of the cell. After it was sequenced using an Illumina MiSeq at the UAF Core lab, I used the online program Base Space to analyze the reads that I got from sequencing. I used Prokka Genome Annotation to identify which genes are present in the bacterium, Kraken Metagenomics to identify what the DNA reads correlated to on different taxonomic levels, and SPAdes Genome Assembler to determine how many contigs were produced from the reads that were produced. Another set of tests that I performed were physiological tests, including testing for oxygen class with fluid thyoglycate, checking for catalase using hydrogen peroxide, checking for cytochrome c oxidase using oxidase test strips, and using an API 20 E test strip to test for various different physiological traits such as Sulphur reduction, which had 20 different tests. All of these are described in the lab 6 handout and were kept in the incubator at 38 degrees Celsius. Finally I used different antibiotic disks to check for its resistance to antibiotics, using Gentamicin, Cefoperazone, Vancomycin, Tobramycin, Amikacin, Trimethoprim, Oxacillin, and Cefazdin. I used the Kirby-Bauer, or disk diffusion test to test for this, described in lab handout 9.

Results: Regarding the gram stain test, my isolate was gram variable, I ensured that the strain was fresh so that the age of the culture was the same throughout the test. Most of the bacterium in the gram stains were gram negative, but a significant amount, about twenty percent, showed up as gram positive. The colonies are a pale, translucent yellow, and are shiny when looked at in the light. They are fairly small as well, usually about a millimeter in diameter and of a normal height. Under the microscope they are round cells.

When looking at the genetic tests, most of the identified strains in the Korona test are Micrococcus luteus. The identified reads only made up a total of twenty seven percent of the total reads, but the majority of those reads were for M. luteus. The confidence on that reading is decently confident, evidenced by the blue coloring. The results of this analysis are shown in table 1.

Table 1: Graph from Korona showing the percent reads of each organism, and to which taxonomic level.

Table 2: Graph of the genomic reads by taxonomic level using Korona. M. luteus is the majority of reads on the species level.

When performing tests for physiological traits, the results were limited. When using a fluid thyoglycollate test it resulted in the isolate being a strict aerobe, with all of the bacterium being at the top of the medium where it is oxygenic. The oxidase test was negative, as the strip did not change color at all, where it would have turned purple if it was positive. The catalase test did return positive by bubbling, indicating that it does have the ability to break down the radical hydrogen peroxide into diatomic oxygen and hydrogen. Finally, when looking at the API 20E strip none of the results returned positive despite the culture being active and fresh from being streaked recently.

When looking at the antibiotic test results, the isolate is resistant to none of the applied antibiotics, and is only lightly to intermediately resistant to oxacillin. The Gentamicin, Cefoperazone, Vancomycin, Tobramycin, Amikacin, Trimethoprim, and Cefazdin antibiotics showed obvious susceptibility, with most of them having enormous rings of 50 to 52 millimeters while the threshold for resistance is only 15 millimeters. Of those only Vancomycin was closer than 50 millimeters, being 38 millimeters.

Discussion: When looking at all of the results for my isolate, they are not all consistent with Micrococcus luteus. The Gram stain, while it was gram variable, does not ideally match with the genetic test that resulted in Micrococcus luteus, which can be gram variable but is usually gram positive (Bonjar). On top of that, most of the bacterium that were stained were gram negative, which conflicts with this result. The negative oxidase result conflicts with M. luteus (Public Health England). The API 20 E test strip results revealed nothing about what the isolate uses as an electron acceptor because every result was negative, and that it likely only uses glucose as an energy and carbon source and oxygen as its electron acceptor. It did not reduce sulphur, digest gelatin, or reduce nitrate, among some of the more interesting tests, which all disagree with M. luteus. I suspect that the API 20E test strip results were negated by having used an inactive colony, as the fluid thyoglycate test failed as well. These results might not be trustworthy.

Many of the tests did line up with M. luteus though, such as the fluid thyoglycate test, which showed that it was an obligate aerobe. M. luteus is an obligate aerobe (Medical Laboratories). The positive catalase result lines up with M. luteus (Public Health England). The colony morphology of being yellow, shiny and smooth line up perfectly with M. luteus (Public Health England). The antibiotic resistance test showed only minor resistance to the antibiotic Oxacillin, which is likely due to a chance inheritance in the population or complete chance because of the weak strength. The organism itself is susceptible to almost all drugs, with a few strains being resistant to nitrofurantoin, macrolides and lincomycin (Public Health Canada). This lines up with M. luteus’ resistances from the tests.

The Micrococcus genus is known to be found on dust particles, in water, on skin and skin glands in vertebrates, and some species can be found in milk. They are fairly ubiquitous in the environment, and are small (0.5 to 3.5 micrometers in diameter) and non-motile. This fits well with where I sampled my bacterium from, as a shower drain is a place where both dust and water would accumulate, along with residues of skin glands from showering. It is an opportunistic pathogen, only pathogenic enough to cause disease in weakened immune systems (Medical Laboratories). The colony morphology is the same as well, being round, shiny, and sort of flat (Medical Laboratories).

When looking back at all the data, it is fairly likely that the isolate is Micrococcus luteus, especially when looking at the fluid thyoglycate test, the colony morphology, and the antibiotic susceptibility. The tests that did not agree were most likely from not having an active colony used in the experiment, such as the oxidase test being negative or the API 20 E test strip showing that the isolate did not reduce nitrate, which it does, referencing Medical Laboratories. I also had to do the thyoglycate test 3 times to get a conclusive result, further making me skeptical of how active the culture was during the physical tests during week 6, which is where almost all of the inconsistencies arose.

If I were to continue researching this isolate, I would redo the API 20 E test strip with a fresh, active culture to ensure that it can reduce nitrate, and also the oxidase test to ensure that it does have cytochrome c oxidase present, which it should according to Public Health England. Further tests that I would do would be testing how much heat resistance it has, the density of a broth suspended sample using a dilution series, test for more antibiotic resistances, and how well it can grow in antibacterial mediums and mediums of different pH levels.



Works Cited

  1. Perkins1, Sarah D., Jennie Mayfield2, and Victoria Fraser3 And. “Sarah D. Perkins.”Applied and Environmental Microbiology. N.p., 01 Aug. 2009. Web. 20 Mar. 2017. <https://aem.asm.org/content/75/16/5363.full>.
  2. Government of Canada, Public Health Agency of Canada. “Micrococcus – Public Health Agency of Canada.”Micrococcus – Public Health Agency of Canada. Public Health Agency of Canada, 19 Apr. 2011. Web. 11 Apr. 2017.
  3. Public Health England. “Bacteria Detail.”Bacteria Collection:. Culture Collections, n.d. Web. 11 Apr. 2017.
  4. The Editors of Encyclopædia Britannica. “Micrococcus.”Encyclopædia Britannica. Encyclopædia Britannica, Inc., 17 Oct. 2007. Web. 11 Apr. 2017.
  5. , E., Dr. “Micrococcus Luteus.”Medical Laboratories. Medical Laboratories, 2013-2014. Web. 11 Apr. 2017.
  6. Lee, Natasha. “DermNet New Zealand.”Microorganisms Found on the Skin | DermNet New Zealand. Dermnet New Zeland, Aug. 2014. Web. 25 Apr. 2017.
  7. h. Shahidi Bonjar. “Evaluation of Antibacterial Properties of Iranian Medicinal-Plants against Micrococcus Luteus, Serratia Marcescens, Klebsiella Pneumoniae and Bordetella Bronchoseptica.”Asian Journal of Plant Sciences  3.1 (2004): 82-86. ANSI.net, 2004. Web. 28 Apr. 2017. <https://docsdrive.com/pdfs/ansinet/ajps/2004/82-86.pdf>.

The Presence of Micrococcus luteus in Canis lupus familiaris


Microorganisms consist of a single cell or cell cluster, and can also include viruses, which are considered to not be cellular (Madigan et al. 2015). The number of microorganisms in the world is too enormous to count or even comprehend, but if we look at a smaller sample, studying these microbes becomes somewhat easier. The sample in this study was taken from the mouth of a dog. It is known that a wide variety of microbes inhabit the mouth of both humans and dogs, but in a study done by Elliot et al. (2005), they found a significant difference in the cultivable oral microbes found in human and dog mouths. They found that the genera most frequently isolated from dog’s saliva were Actinomyces, Streptococcus, and Granulicatella, and the genera most frequently isolated from plaque were Porphyromonas, Actinomyces, and Neisseria (Elliot et al. 2005).

Micrococcus luteus has one of the smallest genomes of free-living actinobacteria sequenced to date (Young et al. 2010). It is a Gram-positive coccus shaped bacterium that belongs to the family Micrococcaceae, it is commonly found on human and animal skin as well as in water and soil. Because M. luteus is a part of the bacteria flora of humans it is not thought of as a pathogenic bacterium, but it is an opportunistic pathogen. In some rare cases, it has shown to give infections in immunocompromised patients (Smith et al. 1999). The genome of micrococcus lutes has shown many similarities with Kocuria rhizophila a closely related organism, and of late the ATCC 9341 strain known as M. luteus was reclassified as K. rhizophila (Tang et al. 2003).

In this experiment, I set out to isolate, characterize and identify a bacterium from an environmental sample. The sample was taken from a dog’s mouth and through a series of physiological test, genome sequencing, and antibiotic testing, characterization of the bacterial sample to the species level was achieved.


In order to identify our environmental sample, I started out with collecting my isolate from a dog’s mouth and placing it on TSA agar (Trypticase soy agar). The plate was inoculated at room temp, without light for five days until the first quadstreak was performed. After every quadstreak the samples were incubated at 37oC for 2-3 days, until the next quadstreak was performed, and then placed in a refrigerator to inhibit growth. In order to try and isolate the bacterial strain a total of five quadstreaks were performed. After the bacterium was isolated it was Gram stained (Lab 4, Gram staining protocol) in order to classify the bacterium and to determine if the culture was pure. Following the Gram staining, genomic DNA was extracted from the latest quadstreak, and sent to sequencing. In order to extract the DNA from the sample we used the PowerSoil DNA Isolation Kit (Lab 5, DNA extraction protocol), and the samples were sequenced in the UAF Core Lab on the MiSeq Illumina Sequencer. In order to analyze our genome sequence datasets, I used BaseSpace Ilumina for the genomic assembly I used the SPAdes genome assembler, to determine taxonomic assignment we used Kraken metagenomics, and to look at the functional gene annotation I used Prokka genome annotation (Lab 7, Bioinformatics protocol).

In order to further characterize my sample several physiological tests (Lab 6, physiological test protocol) were performed. A fluid thioglycolate test in order to determine the oxygen class of the bacterium, an oxidase test to determine if the strain had cytochrome C oxidase, a catalase test to see if the strain had the enzyme catalase, and a API 20 E test strip was used to look at 21 different physiological processes. The API 20 E test strip was incubated for 3 days in 37oC, while the test tubes from the fluid thioglycolate test were stored I room temp for 3 days.

The last procedure that was performed was an antibiotic disc diffusion test (Lab 9, Disk diffusion test protocol), to assess the susceptibility or resistance of our isolate to a variety of different antibiotics. Eight different antibiotics were tested: oxacillin, gentamicin, piperacillin, amikacin, clindamycin, trimethoprim, cefoperazone, and vancomycin.

Most of the data were collected and analyzed over a span of several weeks. DNA analysis of the isolate gave 98.86 % confidence to the species level for Micrococcus luteus, and only 19% of the sample was unclassified (Figure 1). All the analysis performed by BaseSpace showed results that were either equal to or above the guideline.

Figure 1. Results from the genomic sequencing using Kraken Metagenomics and Krona, in BaseSpace Illumina.


The identification test performed on the isolate are summarized in table 1.   The isolate tested positive for both the catalase test and the oxidase test, indicating that the isolate contained the enzyme catalase and cytochrome c oxidase. The gram stain came out red, but because both rods and cocci were observed, the culture was considered to not yet be pure, and more isolation attempts were needed. From the 8 different antibiotics tested, the isolate was susceptible to 6 of them, it was resistant to oxacillin and intermediate resistant to trimethoprim. The zone measurement for oxacillin was 5 mm while the zone measurement for trimethoprim was 13 mm. The other antibiotics tested were gentamicin, piperacillin, amikacin, clindamycin, cefoperazone, and vancomycin.

Table 1. Results for various identification test for the isolate.

Identification test Result
Gram Staining Mixed culture (red)
Catalase test Positive
Oxidase test Positive
Fluid thioglycollate test Facultative
Antibiotic resistance: Disk diffusion test Resistant to oxacillin and intermediate resistance to trimethoprim.
API 20 E test strip See Figure 2

From the last physiological test done, the API 20 E (Figure 2), 7 of the 23 tests performed were positive. The positive test was the LDC, URE, TDA, GEL, SOR, OX, and NO2 tests (Figure 2).

Figure 2. Results from the API 20 E test strip


M. luteus is described as the type species of the genus Micrococcus (Stackebrandt et. al. 1995), and is commonly found on human skin, and on animals, it can also be found in the mouth, and in the upper respiratory tract of animals and humans. The bacterium can likewise inhabit many other areas in the environment, like water, dust, and soil (Kocur et al. 2006).

In relation to the literature, the physiological test results were mostly consistent with information found. Nevertheless, there was one inconsistency found with the fluid thioglycollate test. I observed the bacterium to be facultative, although literature describes the bacteria as an obligate aerobe (Kocur et al. 2006). This may be due to human error or to the sample being impure.

The genus Micrococcus was first described more than a hundred years ago, but since then the description has been revised several times (Stackebrandt et. al. 1995). Today it is clear that this genus of bacteria is gram-positive, cocci shaped and catalase positive (Stackebrandt et. al. 1995). During our research, I found our isolate to be a mixed culture, and not gram positive as literature states. When observing the isolate under the microscope after gram staining it appeared red, with both rods and cocci present. Several isolation attempts were done, but the two bacteria observed seemed to live in symbiosis which complicated the isolation process. However, isolation was achieved after several quadrant streaks.

Numerous interesting studies have been done on the genus Micrococcus and their traits. Dib et al. (2013) discussed how genes present on the plasmids of Micrococcus bacteria can give advantageous features to their respective hosts like antibiotic and heavy metal resistances, the ability to degrade cholesterol, and osmotolerance. A study conducted by Greenblatt et al. (2004) looked at survival of Micrococcus in extreme environments. They found that M. luteus and other closely related cocci that are non-spore-forming seem well suited to extreme environments, all due to special individual factors (Greenblatt et al. 2013). Research has been done on M. luteus superior ability to absorb radiation through pigments that absorb long-wave UV radiation, between 350-475 nanometers, and the researchers hope to implement this into sunscreen and other cosmetic products (SINTEF 2013).

For further research, it would be interesting to look more closely at some of the traits that make M. luteus so good at surviving in extreme conditions, and absorb such long wavelengths of radiation. I only looked at some physiological traits of the bacterium, it would be interesting to see how these aid the bacterium in extreme settings, like the ones previously mentioned.

Our research looked at bacteria within our environment, and our sample was taken from a dog’s mouth where we found the bacterium M. luteus. We conducted several physiological and antibiotic tests, along with genome sequencing in order to understand and characterize the bacterium. Most of the test that we conducted were consistent with literature, but there were some variances within gram staining and the fluid thioglycollate test. However, the tests gave us important information about the bacterium and a better understanding of the environment it lives in.


Literature Cited

Dib, J., Liebl, W., Wagenknecht, M., Farías, M., & Meinhardt, F. (2013). Extrachromosomal genetic elements in Micrococcus. Applied Microbiology & Biotechnology, 97(1), 63-75.

Elliott, D. R., Wilson, M., Buckley, C. M., & Spratt, D. A. (2005). Cultivable Oral Microbiota of Domestic Dogs. Journal of Clinical Microbiology, 43(11), 5470-5476.

Greenblatt, C. L., Baum, I., Klein, B. Y., Nachshon, S., Koltunov, V., & Carlo, R. J. (2004). Micrococcus luteus – Survival in Amber. Microbial Ecology, 48(1), 120-127.

Kocur, M., Klosss, W. E., & Schliefer, K. (2006). The Genus Micrococcus. Prokaryotes, 3, 961-971.

Madigan, M. T., Martinko, J. M., Bender, K. S., Buckley, D. H., & Stahl, D. A. (2015). Brock biology of microorganisms (Fourteenth edition.). Boston: Pearson.

SINTEF. (2013). Super sunscreen from fjord bacteria. ScienceDaily. Retrieved April 17, 2017 from www.sciencedaily.com/releases/2013/08/130806091556.htm

Smith, K. J., Neafie, R., Yeager, J., & Skelton, H. G. (1999). Micrococcus folliculitis in HIV-1 disease. British Journal of Dermatology, 141(3), 558-561.

Stackebrandt, E., Koch, C., Gvozdiak, O., & Schumann, P. (1995). Taxonomic Dissection of the Genus Micrococcus: Kocuria gen. nov., Nesterenkonia gen. nov., Kytococcus gen. nov., Dermacoccus gen. nov., and Micrococcus Cohn 1872 gen. emend. International Journal of Systematic Bacteriology, 45(4), 682-692.

Tang, J. S., & Gillevet, P. M. (2003). Reclassification of ATCC 9341 from Micrococcus luteus to Kocuria rhizophila. International Journal Of Systematic And Evolutionary Microbiology, 53(4), 995-997.

Young, M., Artsatbanov, V., Beller, H. R., Chandra, G., Chater, K. F., Dover, L. G., … Greenblatt, C. L. (2010). Genome Sequence of the Fleming Strain of Micrococcus luteus, a Simple Free-Living Actinobacterium . Journal of Bacteriology, 192(3), 841—860.


Micrococcus luteus in a Veterinary Clinical Setting

Micrococcus luteus in a Veterinary Clinical Setting

Erin Murray

Biol 342, Section F02



In veterinary clinics or hospitals, it is highly important to maintain as clean an environment as possible for the sake of their patients’ health. Failure to do so carries the possibility of inadvertently transferring bacterial or viral pathogens from one patient to the next, which could result in a healthy patient becoming sick simply from having visited the clinic. This is known as a nosocomial infection (Stull and Weese). If a patient is hospitalized and acquires a nosocomial infection, this could lead to its hospital stay being prolonged (Harper et al.). Microbes known to cause nosocomial infections have been isolated from samples taken from various surfaces around veterinary clinics, including medical equipment used on patients, as well as from air samples from the various rooms of an animal hospital (Harper et al.). This means that airborne bacteria could potentially land on and colonize surfaces of medical equipment even after they have been thoroughly cleaned.

In the study of airborne sampling, the most commonly isolated bacteria belonged to the genus Micrococcus (Harper et al.). Micrococcus species commonly grow on Mammalian skin as a commensal bacteria, and are rarely ever pathogenic. There have been rare cases where patients developed infections from Micrococcus bacteria becoming an opportunistic pathogen, but this has only occurred in patients that were immunocompromised (Hanafy et al., Public Health England).

The purpose of this study was to attempt to determine if any pathogenic bacteria were taking up residence on the surfaces of the medical equipment at a local emergency veterinary clinic. Speaking from personal experience, one potential source of contact transfer of microbes is a veterinarian’s or technician’s stethoscope. Though it is used on every patient walking through the doors of the clinic, the cleaning of this piece of medical equipment can be easily overlooked. Many veterinary staff will wear their stethoscope around their neck in order to keep it close at hand and may not get a chance to, or may even forget to, disinfect it in between patients.

I hypothesized that I would find species of bacteria that typically lived either on Mammalian skin and hair, or in canine or feline mouths. I suspected that I might find mouth bacteria because dogs and cats lick their fur to groom themselves. From this hypothesis I predicted that I would isolate a bacterium that could at least tolerate oxygen and would therefore be an aerobe or an aerotolerant anaerobe.



The diaphragm of a frequently used stethoscope at a local veterinary clinic was swabbed with a sterile cotton swab that had been wetted with sterile water. The swab was then used to inoculate a Tryptic Soy Agar (TSA) plate. The plate was sealed with parafilm and was stored at room temperature for one week to allow for bacterial colonies to grow. At the end of one week, several colonies of different colors and textures had grown, and one colony was selected to be isolated. The colony was goldenrod yellow in color, circular and raised, had a smooth and shiny finish, and was about the size of a pencil eraser. A sample of the colony was transferred onto a new TSA plate using the quadrant streak technique as outlined in the handout for Lab 2: Aseptic Technique. The plate was incubated at 37 °C to accelerate colony growth. A new quadrant streak was performed every 3-4 days for a total of 4 times to ensure that purity of the culture had been achieved.

A series of physiological tests were performed on the isolate to determine its physiological characteristics. A Gram stain was performed on a microscope slide of the culture, following the protocol as outlined in Lab 4: Staining Techniques, to determine the type of cell wall the bacteria possessed. Following the protocols as outlined in Lab 6: Physiological Testing of Your Isolate, a fluid thioglycollate test was performed to determine the culture’s oxygen class, an oxidase test was performed to determine whether the isolate produced the cytochrome c oxidase enzyme, and a catalase test was performed to determine whether the isolate produced the catalase enzyme. An API 20E test strip was performed, following the protocol as outlined in Lab 6, to determine which materials the bacteria could metabolize. The test strip was rechecked after 24-48 hours of incubation at 37 °C. Later on, an API Staph test strip was also performed, following the protocol on the API Staph handout. It, too, was incubated at 37 °C and rechecked 24-48 hours later.

The culture’s susceptibility and/or resistance to various antibiotics was tested, following the protocol as outlined in Lab 9. The antibiotics used for the test were amikacin, cefazolin, clindamycin, erythromycin, gentamicin, oxacillin, tetracycline, and tobramycin.

DNA was extracted from the isolate for genomic analysis, using the PowerSoil DNA isolation kit and following the protocol as outlined in the handout for Lab 5. The DNA sample was then submitted to the UAF DNA Core Lab to be sequenced. When the raw genomic data had been obtained, it was then analyzed on BaseSpace, using the SPAdes Genome Assembler, Kraken Metagenomics, and Prokka Genome Annotation programs. The contig data was then analyzed using the NCBI Nucleotide BLAST program.



Gram staining of the bacterium revealed that the isolate was a Gram-positive cocci that formed tetrads and irregular clusters. In fluid thioglycollate the bacteria grew directly on and just below the surface of the fluid, and no growth was observed in the anoxic layer of the fluid, therefore the bacterium is likely a strict anaerobe. The isolate tested positive for the presence of the enzymes catalase and cytochrome c oxidase. The API 20E and API Staph assays had no positive results. Antibiotic resistance testing revealed that the isolate was susceptible to amikacin, cefazolin, clindamycin, gentamicin, tetracycline, and tobramycin, was intermediately susceptible to oxacillin, and was resistant to erythromycin.

SPAdes Genome Assembler discovered 300 contigs with the largest contig being 61,411 base pairs (bp). The total length of the genome was determined to be 2.51 Mbp, and the GC content of the genome was determined to be 72.72%. Prokka Genome Annotation discovered 53 tRNAs, 0 rRNAs, 1 CRISPR gene, and 2270 CDs. The Kraken Metagenomics program took 173,940 reads. Of those reads, 55,285 were classified, resulting in 31.78% of total reads being classified. 25.85% of the total reads were classified to the species level, and the bacterium was identified as Micrococcus luteus. Analyzing contigs via BLAST revealed that the sequence from node 21 was a 97% match to the genomes of the NCTC 2665 and trpE16 strains of M. luteus.



After extensive testing of the isolate, it has been concluded that the identity of the isolate is Micrococcus luteus.

M. luteus is described in the literature as an aerobic, catalase- and oxidase-positive, Gram-positive non-motile cocci which form tetrads, with colonies being yellow in pigment, convex and smooth in texture with regular edges (Public Health England, Whitman et al.). The physical appearance of colonies of the isolate grown on agar plates, and physiological tests performed on the isolate are in agreement with these descriptions. Genome length and GC content of the isolate that were reported in SPAdes also agree with values in the literature (Hanafy et al., Whitman et al.)

Neither of the API assays that were attempted had any color changes, meaning that none of the tests came back positive. For the API 20E test, the lack of positive results is likely due to the test being the wrong fit for this microbe – it was meant to be used on Gram-negative anaerobes, and the isolate was a Gram-positive strict aerobe. It is possible that the reagents were unable to penetrate the thick peptidoglycan layer of the bacteria’s cell walls in order for metabolism of the reagents to occur.

The API Staph test should have been the best fit for the isolate. However, it still came back with no positive results. Researching the literature reveals that M. luteus should be able to metabolize glucose, fructose, sucrose, and mannose (Hanafy et al.), meaning that the GLU, FRU, SAC, and MNE wells on the API Staph test should have had color changes to indicate positive results. Some strains have been found to also metabolize maltose and trehalose, contrary to prior data indicating that these molecules were not utilized by M. luteus (Wieser et al.), meaning that there possibly could have been positive results from the MAL and TRE wells if the isolate was a similar strain. The literature also indicates that M. luteus is urease positive (Whitman et al.), so the URE well should have indicated a positive result as well. The lack of results from the API Staph test was probably due to not having a fresh enough sample: the instructions for the test call for a sample that is 18-24 hours old, and the plate that the sample was taken from had been incubating for between 4 and 7 days.

The isolate was found to be susceptible to most of the antibiotics that were tested, except for erythromycin, which it was completely resistant to. Resistance to erythromycin has been found to be due to a plasmid present in a strain of M. luteus isolated from human skin (Liebl et al.). With humans and companion animals having such an intimate relationship and being in contact with each other so often, it doesn’t take a stretch of the imagination to suggest that erythromycin-resistant M. luteus could be transferred from human skin onto the skin of a companion animal, or vice versa, which would explain the presence of erythromycin-resistant M. luteus on a stethoscope in a veterinary clinic. Horizontal gene transfer of this resistance plasmid could potentially cause other bacterial species to develop resistance as well.

Further investigation into the types of bacteria growing on medical equipment in veterinary clinics should be pursued. Only one of several different colonies from the original swab of the stethoscope was chosen for further evaluation. Analysis of the other colonies that were present on the original TSA plate would be the first step in continuing the investigation, followed by taking samples from other objects and equipment, and possibly obtaining airborne samples from around the clinic. This type of investigation would be very helpful in assessing local clinics’ risk of exposing their patients to nosocomial infections.



Figure 1. Macroscopic and microscopic morphology of the isolate. Colonies are yellow, convex, and smooth in texture with a regular edge. Gram staining reveals that the bacteria are Gram-positive cocci that form tetrads and irregular clusters.

Figure 2. Antibiotic resistance testing of the isolate. The isolate showed resistance to erythromycin, but to no other antibiotic which was tested.

Figure 3.  Krona Classification chart from the Kraken Metagenomics program. The reads were classified and nested into successive taxonomic groups, down to the species level.



Hanafy R.A., Couger M.B., Baker K., Murphy C., O’Kane S.D., Budd C., French D.P., Hoff W.D., and Youssef N. 2016. Draft genome sequence of Micrococcus luteus strain O’Kane implicates metabolic versatility and the potential to degrade polyhydroxybutyrates. Genomics Data 9:148—153.

Harper T.A., Bridgewater S., Brown L., Pow-Brown P., Stewart-Johnson A., Adesiyun A.A. 2013. Bioaerosol sampling for airborne bacteria in a small animal veterinary teaching hospital. Infection Ecology and Epidemiology 3.1.

Liebl W., Kloos W.E., and Ludwig W. 2002. Plasmid-borne macrolide resistance in Micrococcus luteus. Microbiology 148:2479—2487.

Public Health England 2014. Identification of Staphylococcus species, Micrococcus species and Rothia species. Bacteriology — Identification 3:1-32.

Stull J.W., and Weese J.S. 2015. Hospital-Associated Infections in Small Animal Practice. Veterinary Clinics: Small Animal Practice 45:217—233.

Whitman M., Goodfellow M., Kämpfer P., Busse H.J., Trujillo M., Ludwig W., Suzuki K.I. 2012. Bergey’s Manual of Systematic Bacteriology: Volume 5: The Actinobacteria. Springer Science & Business Media, p. 574-575.

Wieser M., Denner E.B.M., Kämpfer P., Schumann P., Tindall B., Steiner U., Vybiral D., Lubitz W., Maszenan A.M., Patel B.K.C., Seviour R.J., Radax C., and Busse H.J. 2002.  Emended descriptions of the genus Micrococcus, Micrococcus luteus (Cohn 1872) and Micrococcus lylae (Kloos et al. 1974). International Journal of Systematic and Evolutionary Microbiology 52:629—637.

Cheek Swab Reveals Presence of Stapholococcus aureus in Oral Cavity of some Individuals

Cheek Swab Reveals Presence of Stapholococcus aureus in Oral Cavity of some Individuals

Mike Fierro

Uaf undergraduate and BIOL 342 student



From childhood we learn about the different environments around the world ranging from the tundra of the arctic to the arid sands of the desserts; with further research we discover the animals that are able to thrive in these environments through adaptations to the conditions.   It’s easy to focus on a narrow range of environments to ones we are able to encounter through exploration, and to limit our knowledge of organisms to animals we may come across in those areas we can reach.   But what about environments that we don’t think about as being environments? Environments aren’t always large tracts of land or a lake system.   What if the area a creature inhabits is unlike any you will ever come across and yet at the same time you are more connected to than any place that you could find on a travel?   What if the environment… is you?

With over 700 bacterial species known, the human oral cavity is a perfect home for many bacteria.   Bacteria are able to grow on several sites in the mouth including the tongue dorsum, lateral sides of tongue, buccal epithelium, hard palate, soft palate, supragingival plaque of tooth surfaces, subgingival plaque, maxillary anterior vestibule, and tonsils (Aas et al. 2005).   There are numerous benign as well as opportunistic pathogens that inhabit the oral cavity as well including Staphylococcus aureus, Streptococcus mitis, and Steptococcus pyogenes as well as species of the yeast Candida (Lab 10).   The objective of this study to isolate a bacteria and perform both physiological and genetic tests to determine its identity as well as how and where it survives.   With a simple swabbing of the inside my cheek, I am making the attempt to find an organism that calls the human oral cavity home.


A sterile swab was used to rub several times against the inside of my cheek, avoiding other areas of the mouth.   The sample was quickly inoculated onto two microbial growth media mediums: a tryptic soy agar (TSA) plate, as well as a Sabouraud’s agar (SA) plate, where it was allowed to grow at around 23 ºC for several days.

In lab the original TSA sample was kept and four different quadrant streaks were carried out throughout the next couple weeks in order to purify the isolate.   After these attempts to purify the culture, a series of physiological and genetic tests were used in order to obtain an identity of the bacteria isolated from the cheek swab.   The physical tests included a Gram stain, fluid thioglycollate test, oxidase test, catalase test, and an API-20E test, while DNA purification followed by a BaseSpace analysis was used as a genetic test of the isolate.

Three weeks into the project, the most recent TSA plate was used in order to perform a Gram stain (Lab 4 protocol), which would identify if the cell wall of the bacteria had a thick (positive Gram stain) or thin (negative Gram stain) peptidoglycan layer.   A positive Gram stain dyes the cells a dark purple due to crystal violet being encased in the cell wall due to dehydration of the peptidoglycan layer followed by addition of Safranin, whereas crystal violet is removed by ethanol from a Gram negative cell and the cell turns a light pinkish red after the introduction of Safranin.

Five weeks from original sampling, three physiological tests were performed on a fresh culture sample.   The fluid thioglycollate test was carried out (Lab 6 protocol) in order to determine the oxygen class of the isolate.   The solidified agar is a barrier to oxygen, so the bottom of the test tube is anoxic while the top has oxygen available.   This test reveals if the bacteria is able to grow only in the presence of oxygen (strict aerobe), grow regardless but better with oxygen (facultative aerobe), grow just below the surface (microaerophile), only grow without oxygen’s presence (strict anaerobe), or equally throughout (aerotolerant anaerobe).   The oxidase test was used (Lab 6 protocol) to determine the presence or lack of cytochrome oxidase, which differentiates bacteria into pseudomonad species (oxidase positive) and enteric species (oxidase negative).   The catalase test reveals the presence of the catalase enzyme, which protects cells that have it from reactive oxygen species including hydrogen peroxide.   By neutralizing these oxygen species, the cell is protected from oxidative damage.   The API-20E test is comprised of twenty physiological tests which characterize the Gram negative bacteria.   The characteristics tested are an indication of what the bacteria is able to ferment as well as production of certain enzymes and ability to oxidize reactants.

A DNA extraction was performed (Lab 5 protocol) in order to obtain the genomic sequence of the bacterial isolate.   The extraction is carried out in three main steps: cell lysis, removal of inhibitors and proteins, and obtaining a pure solution of DNA.   Cell lysis is accomplished by physical means of using beads to batter the sample, chemical means to dissolve the cell wall, and by enzymes that break down chunks of cell wall, which allow the cell’s contents to be exposed.   Proteins and inhibitors are used by introducing chemical substances that extract these from the solution followed by centrifugation.   During the centrifugation, the DNA is bound to a solid matrix while the inhibitors and proteins are part of the supernatant.   In the last step, DNA is removed from the solid matrix, centrifuged again, and appears in the resulting supernatant.

The last test on the isolate performed was to determine its antibiotic susceptibility (Lab 9 protocol).   Seven antibiotic discs in total were placed among the isolated culture to determine if zones of inhibition were produced by the antibiotics that prevented its bacterial growth.   The antibiotics tested included tobramycin, cefazolin, vancomycin, cefoperazone, trimethoprim, gentamicin, and amikacin.   The results were compared to known susceptibility thresholds of each antibiotics in order to determine efficacy of the antibiotic.


After the first 24-hour period after inoculation, no colonies were evident on either plate.   After 72 hours, numerous colonies of varying sizes were forming on the TSA plate compared to one large colony on the SA plate.   After five days, the number of colonies on the TSA plate had reached double digits while the SA plate still had one major colony with a couple smaller colonies on the side.   After one week’s time, the TSA plate had around 30 colonies; there was one large colony, four colonies larger than 1mm, and the amount of pencil-tip sized colonies was in the double digits.   On the SA plate, however, there was no noticeable growth than observed on day 5.

Figure 1. A comparison between colonies formed on SA plate (left) and TSA plate (right).

The results of the physiological tests will be discussed first.   Under the microscope, there was Gram negative bacteria along with Gram positive bacteria.   The sample was continuously purified thereafter until the resulting bacteria was completely Gram positive.   The fluid thioglycollate test revealed that growth occurred more on the surface than the underlying agar.   The oxidative test on the bacterial isolate was a yellow/buff color, which occurs when the test is negative.   The catalase test showed that the isolated bacterial bubbled when exposed to hydrogen peroxide.   This is a positive result to the catalase test.   The original API-20E test revealed that the bacterial contaminant did not have gelatinase and thus couldn’t break down gel, could oxidize nitrate to nitrite, had a positive citrate test, and was able to ferment glucose, mannitol, inositol, sorbitol, rhamnose, sucrose, meliblose, amygdalin, and arabinose.   The bacteria had large zones of inhibition on all antibiotics tested.

Figure 2. Picture of contaminated Gram stain.                         Figure 3. Example of zone of inhibition.

Figure 4. Picture of thioglycollate test.                                       Figure 5. Picture of contaminant API-20E test.



The genetic results showed that the number of contigs in the sample tested was in the hundreds, the total length was in the millions, and the largest contig was over 100,000 bp.   The result of the BaseSpace analysis was that 97% of all contigs were able to be read; of those contigs, there was a 99.94% match with known samples of Staphylococcus aureus.

Figure 6.   Pie diagram and bar graph results of BaseSpace test revealing Staphylococcus aureus as isolate.


                      TSA favors bacterial growth while SA provides a better medium for fungal growth to thrive.   The reason more colonies grew on the TSA plate was because more colonies were bacterial and made more use of the medium that favored them.   The reason colonies existed on the SA plate was because either there was a fungus within the cheek, or there was bacteria that was able to survive with the resources available in the SA plate.

The original Gram stain result of both Gram positive and Gram negative bacteria proves the bacterial sample was not pure.   A purified sample of bacteria would be one or the other, unless the bacteria is Gram variable, which is very rare and did not match the known scientific literature with the results of the genomic sequencing.   The gram positive result on the culture after further purification did agree with scientific literature.   Under the microscope, the bactieria formed clusters of round cells.

The fluid thioglycollate test shows the bacteria is a facultative anaerobe as it grows more when oxygen is available, but is able to survive when oxygen is not present.     The negative result on the oxidase test reveals the bacterial isolate is an enteric species, while the positive catalase test reveals that the culture has a resistance to reactive oxygen species and thus protects the cell from oxidative damage The API-20E test results showed that there was a Gram negative bacteria present in the culture that was not present in later Gram stains.   Unfortunately, an API-Staph was not carried out since the writer of this paper missed the part about API-20E working on Gram negative bacteria only when he had decided the isolate was Gram positive.   The antibiotic disc test revealed the isolate is highly susceptible to all seven antibiotics tested when compared to their susceptibility thresholds.

The number of contigs, total length, and the size of the largest contig were all statistically meaningful (Lab 7 protocol).   The high amount of readable contigs as well as the nearly identical comparisons between laboratory results and scientific literature suggest to the utmost that the bacteria isolated from the cheek swab is Staphylococcus aureus.

Using the API-20E test, the Gram negative result, and the observations of the bacterial contaminant under a microscope, it would be possible for future research to determine the identity of this contaminant.   It is interesting that the contaminant yielded a catalase positive, oxidative negative, and citrus positive result, all of which are shared by the Gram positive Staphylococcus aureus that was isolated.   I attribute this to the similarity of the environment from which these bacteria were isolated.

The remainder of this paper will discuss the bacterial isolate.   Staphylococcus aureus is found in clusters of round cells in the nasal passages, oral cavity, lower reproductive tract, and skin of humans as well as other animals such as the dogs of healthcare workers (Masalha et al. 2001).   It’s estimated that 20-30% of people are long term carriers (Tong et al. 2015).     Usually a commensal bacteria, it becomes an opportunistic pathogen when circumstances allow and cause ailments ranging from minor skin infects and food poisoning to life-threatening diseases such as pneumonia, endocarditis, toxic shock, and sepsis (MedlinePlus 2017).   Once it’s inside the bloodstream, Staphylococcus aureus has enzymes to clot blood and destroy proteins, can secrete toxins, and has super-antigens that cause organ failure by causing the immune system to become hyper-reactive.   Antibiotic-resistant strains such as methicillin-resistant Staphylococcus aureus (MSRA) are becoming increasingly abundant and are a major concern in the medical field due to transmissions in hospitals.   Over half a million people in US hospitals contract Staph infections, and most are caused by Staphylococcus aureus (Bowersox 1999).   Staphylococcus aureus is here to stay; it would benefit us to further research this bacteria to better understand it to aid in limiting its role as an opportunistic pathogen that has taken a countless amount of lives.



Works Cited:

Aas J; et al. (2005). “Defining the Normal Caterial Flora of the Oral Cavity’. J Clin Microbiol. November 2005. 43(11) 5721-5732.

Bowersox, John (27 May 1999).  “Experimental Staph Vaccine Broadly Protective in Animal Studies”. NIH. Archived from  the original  on 5 May 2007. Retrieved  28 July  2007.

Masalha M; et al. (2001).  “Analysis of Transcription of the Staphylococcus Aureus Aerobic Class Ib and Anaerobic Class III Ribonucleotide Reductase Genes in Response to Oxygen”.  Journal of Bacteriology.  183  (24): 7260—7272.

MedlinePlus [Internet]. “Staphylococcal Infections”. Bethesda, MD: National Library of Medicine, USA.  Skin infections are the most common. They can look like pimples or boils.

Tong SY; Davis JS; Eichenberger E; Holland TL; Fowler VG (July 2015).  “Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management”

UAF Lab handouts provided to me by Mary Beth Leigh.