Identification of Unkown Culture: Enterobacter Cloacae - Essay Example

"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.