Citrobacter freundii - Lab Report Example

PURPOSE MENT In a microbiology lab, one of the most important activities carried out is determination of the identity of unknown microorganism. This is a core practice when studying diseases discovered in a patient, to know the causative agents and possible treatments. Intuitively, this study makes use of the knowledge acquired from microbiology laboratory sessions to establish the identity of unknown bacterium #20.MATERIALS AND METHODSUnknown #20 was obtained from the instructor. The procedure followed was as stated in Bergey’s manual.

The unknown was streak out using the T streak method, in the presence of Trypticase Soy Agar plate. The plates were placed in an incubator and grown while observing the morphology. A Gram stain was performed on the unknown alongside quality control bacteria. The gram reaction was observed and recorded and specific biochemical tests performed. Given the reaction gave out a gram negative rod, the first test performed was oxidase test. Other tests performed are listed in the table found in the results section.

Biochemical test performedGram stainOxidase testBCP lactoseIndole testCitrate testMotility testRESULTSThe following tablet lists all the biochemical tests carried on the unknown microorganism:TESTPURPOSEREAGENTSOBSERVATIONSRESULTSGram stainTo establish reaction of the microorganism on the gram stainAlcohol, iodine, crystal violet, safraninpink rodsGram negative rodsOxidase testTo establish the presence of cytochrome cOxidase paperBlack color changePositive oxidase testBCP lactoseTo study the fermenting effect of a bacterium on a given carbohydrateNonePurple to yellow color changePositive lactose fermentedIndole TestTo study if an organism can split indole from trytophaneMixture of kovac’s and 1 ml tryptone brothRed ring witnessed at top of brothnegative indole testCitrate testTo determine the ability of organism to utilize citrate as a the sole means for carbon and energySimmons Citrate agarColor change to bluePositive citrate testMotility testTo determine the motility of an organism by means of flagellaSemi-solid medium containing tetrazolium chloride indicatorFuzzy pink color observed from the stab linePositive motility testFigure showing flowchart to determine the identity of the organism:Unknown #20Gram stainGram negative rodOxidase test (positive) Positive negativeCitrobacter freundii Proteus vulgarisEnterobacter aerogenes Proteus mirabilisEscherichia coli Serratia marcescensKlebsiella oxytoca Indole test (positive)(Positive) (negative)Escherichia coli Citrobacter freundiiKlebsiella oxytoca Enterobacter aerogenes Klebsiella pneumonia Citrate test (negative)(Positive) (negative)Citrobacter freundii Klebsiella pneumoniaEnterobacter aerogenesMotility (negative) (Positive) (negative)Citrobacter freundii Enterobacter aerogenesHence unknown #20 is Citrobacter freundiiDISCUSSION AND CONCLUSION After all the differential tests were performed, the results showed that the identity of unknown microorganism was citrobacter freundii.

The results were compared against the class chart showing the classifications of the microorganisms. The determination that the unknown organism was gram negative rod initiated use of TSA slant to inoculate the other tests, Oxidase test, BCP lactose, Indole test, Citrate test, Motility test (Fraser, 76). All the results were well worked out for the the tests except for the citrate test which gave a false negative results. The error was noted given that, for this test, the result was inconsistent with other tests.

The test was repeated and was able to give a positive result. In conclusion, the unknown organism was found to be Citrobacter freundii, following a series of eliminations made from the tests. Citrobacter freundii is in the Enterobacteriaceae family and are gram-negative bacilli (Fraser p. 20). It is normally found in sewage and intestinal tract of animals and humans. It can cause disease to its host. Work cited Brenner, Don J, Noel R. Krieg, and James T. Staley. Bergeys Manual of Systematic Bacteriology: Volume Two, Part a.

New York: Springer, 2005. Internet resource.Fraser, Susan L. Enterobacter Infections in Medscape Reference. New York: Willey, 2012. Retrieved from: http://emedicine.medscape.com/article/216845-overview#aw2aab6b2b2