Identification of Unkown Culture: Enterobacter Cloacae – Infections Example

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"Identification of Unkown Culture: Enterobacter Cloacae" is a perfect example of a paper on infections. Enterobacter cloacae is in the Enterobacteriaceae family and are gram-negative bacilli (Fraser 2012). It is normally found in sewage and intestinal tract of animals and humans. It can cause disease to its host thereby making it important to know how to isolate it from a culture of bacteria. In a microbiology lab, determination of unknown organism is one of the core activities carried out especially when evaluating diseases. 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 an unknown bacterium.

In which case, the unknown organism to be identified is enterobacter cloacae. The major concept used during the process is culture purification besides using the bacterial isolation tree. MATERIALS AND METHODS Unknown bacteria were 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 (Boon et al 2001). Other tests performed are listed in the table found in the results section. Biochemical test performed Gram stain Oxidase test BCP lactose Indole test Citrate test Motility test RESULTS The following table lists all the biochemical tests carried on the unknown microorganism: TEST PURPOSE REAGENTS OBSERVATIONS RESULTS Gram stain To establish reaction of the microorganism on the gram stain Alcohol, iodine, crystal violet, safranin pink rods Gram-negative rods Oxidase test To establish the presence of cytochrome c Oxidase paper Black colour change Negative BCP lactose To study the fermenting effect of a bacterium on a given carbohydrate None Purple to yellow colour change Positive lactose fermented Indole Test To study if an organism can split indole from tryptophan A mixture of Kovac’ s reagent and 1 ml tryptone broth Red ring witnessed at top of the broth positive indole test Citrate test To determine the ability of an organism to utilize citrate as a sole means for carbon and energy Simmons Citrate Agar Colour change to blue Positive citrate test Motility test To determine the motility of an organism by means of flagella Semi-solid medium containing tetrazolium chloride indicator The fuzzy pink colour observed from the stab line Positive motility test Arginine test To study if the bacterium can make pH of the medium-rise Arginine dihydrolase broth.

A nutrient broth containing 0.5% arginine The indicator changed colour from purple to yellow Positive arginine test. Figure showing flowchart to determine the identity of the organism: Unknown #20 Gram stain Gram-negative rod Oxidase test (positive) Negative                                                                                                                                     positive Citrobacter freundii                                                                                                                        Proteus vulgaris Enterobacter cloacae                                                                                                                     Proteus mirabilis Escherichia coli                                                                                                                                      Serratia marcescens Klebsiella oxytoca   Indole test (positive) (Positive)                                                                                    (negative) Escherichia coli                                                                Citrobacter freundii Klebsiella oxytoca                                                        Enterobacter cloacae                                                                                                                     Klebsiella pneumonia Citrate test (negative)   (Positive)                                                                                    (negative) Citrobacter freundii                                                    Klebsiella pneumonia Enterobacter cloacae Motility (negative) (Positive)                                                           (negative) Enterobacter cloacae                       Citrobacter freundii Hence unknown #20 is enterobacter cloacae   DISCUSSION AND CONCLUSION Considering all the differential tests were performed in the lab, the outcomes showed that the identity of unknown microorganism was Enterobacter cloacae.

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 the use of TSA slant to inoculate the other tests, Oxidase test, BCP lactose, Indole test, Citrate test, Motility test (Fraser 2012).

All the results were well worked out for the tests except for the citrate test, which gave false-negative results. The mistake 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 Enterobacter cloacae, following a series of eliminations made from the tests as shown by the tree. Enterobacter cloacae are in the Enterobacteriaceae family and are gram-negative bacilli (Fraser 2012).

It is normally found in sewage and intestinal tract of animals and humans. It can cause disease to its host.


Boone, D. R., Castenholz, R. W., & Garrity, G. M. (2001). Bergey's manual of systematic bacteriology. New York: Springer.

Fraser, S. (2012). Enterobacter Infections. Medscape Reference. Web. 13 Oct. 2014. ‹›.

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