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Identification of an unknown bacterium

Identificationof an unknown bacterium

Micro-organismsform an essential part of the environment. When identifying unknownmicrobes, one should pay attention to particular growth factors andbiochemical properties that distinguish make them unique. Accurateidentification of bacteria is necessary for sterility tests becauseit ensures that the product is free from any microbes. Intherapeutics, identifications of microbes help physicians determinethe most effective line of treatment for illnesses caused by bacteria(Murray, Rosenthal &amp Pfaller, 2015). The first part of the testusually considers enzyme activity and production while the secondpart evaluates biochemical reactions such as in the indole and gramstaining methods. The aim of this report was to identify an unknownmicrobe. The unidentified microorganism was exposed to differentenvironmental conditions and results recorded for evaluation so as todetermine the type of bacteria. Additionally, the morphology of themicrobes was also observed to deduce conclusions regarding the typeof organism present.

Materialsand methods


Mediumused to maintain stock culture: I tube T.S. Broth, nitrate solutiontest

OtherMedia used: Alpha-naphthol, KOH, Nitrate test solutions A and B,Water, Oxidase reagents, Grams Iodine

Incubationtime: 48 hours

Equipment’s:Sugar fermentation tubes.

Methods:KOH test and nitrate test were carried out to identify the unknownmicrobe.


Mediumused to maintain stock culture:

Itube T.S. Broth, 1 T.S agar plate, 1 starch plate and glucose brothtube

Incubationtemperature: 32 degrees Celsius

Equipment’s:Urea broth tube and 1% tryptone broth

Methods:The glucose broth tube, urea tube and a tube of 1% tryptone wereinoculated with the unknown microbe


Themedium used to maintain stock culture: 1 tube T.S lysine broth, 1 T.Sagar plate, water, oxidase reagent and Alpha-naphthol.

OtherMedia used: Kovac`s reagent, Grams Iodine, and KOH

Equipment’s:Urea broth tube and 1% tryptone broth

Methods:Oxidase and catalase and Voges-Prokauer tests were done.

Gramreaction was also done.


Supplies:1 T.S agar slant and Simon’s citrate slant

Methods:The unknown sample was streaked on a Simon’s citrate slant andincubated at 32 degrees.






Catalase test

Air bubbles present


Nitrate test

Green color


Tryptan tube

No red color (Appears green)


Urea tube

Orange color


Citrate test

Color change from green to Blue color at the bottom



Red color


Oxidase test

air bubbles present


Lysine test

Turns purple


Sulfide production test

Turns yellow and gas generated


Sucrose tube

Gas production and turns yellow


Indole test

No red band


Conclusion:The results obtained confirmed that the microorganism underinvestigation was Staphylococcusaureus


Afterseveral biochemical tests had been conducted, it was evident that theunknown micro-organism was Staphylococcusaureus. Theabove decision was reached after critical analysis and eliminationtechniques. For instance, oxidase test is used to identify microbesthat produce oxidase enzyme. Its working principle is that when apiece of filter is soaked with drops of oxidase reagent and thespecimen added, air bubbles are generated hence indicating thatphenylenediamine which is present in the reagent has been oxidized.The experimental results also showed positive outcomes forVoges-Prokauer. For Proteusmirabilis and Proteus vulgaris,a negative reaction is usually expected and not positive as was inthis case

Theexperimental results also indicated positive for oxidase test and asa result, Proteusmirabilis and Proteus vulgariswere eliminated. Sulfide production test is done for Proteusmirabilis. Formationof a black color in the medium of the tube confirms the presence ofthe organism, and in this case, only yellow color was generated henceconfirming that the unknown was not Proteusmirabilis (Maza,Pezzlo, Shigei, Tan &amp Peterson, 2013).Interms of differentiating Staphylococcusaureus from Pseudomonas aeruginosa, theinitial produces gas when in a sucrose medium due to fermentationwhile the later has no acid gas.

Lastly,catalase test is used to test for bacteria that produce the enzymecatalase. Enzyme Catalase plays a very important role when it comesto the breakdown of hydrogen peroxide. The byproducts of suchreactions are water and oxygen gas. During the experiment, Proteusmirabilis, Proteus vulgaris, and Staphylococcus aureus gavepositive results for the catalase test expect for Pseudomonasaeruginosa. P. aeruginosa wasthus eliminated again hence confirming that the unknown microbe wasStaphylococcusaureus.


Inconclusion, it was evident that clear that the experiment wassuccessful because the unknown bacteria was identified asStaphylococcusaureus. Inthis case, cellular components, organism`s morphology, andbiochemical characteristics were all put into consideration whenidentifying the unknown microbe. Additionally, despite the experimentbeing a success, a highly standardized result could have beenobtained is molecular techniques such as gene typing and PCR wereused. A limitation that was observed during the experiment that couldhave caused discrepancies in the results included possiblecontamination as the specimen were being moved from one place toanother. Conclusively, the aim of the experiment was achieved.


Dela Maza, L. M., Pezzlo, M. T., Shigei, J. T., Tan, G. L., &ampPeterson, E. M. (2013).&nbspColoratlas of medical bacteriology&nbsp(No.Ed. 2). ASM Press.

Murray,P. R., Rosenthal, K. S., &amp Pfaller, M. A. (2015).&nbspMedicalmicrobiology.Elsevier Health Sciences.