Question

What bacteria might be, lower portion is my results. Thanks

Answer 1

Based on the information provided in the images. The test results indicate the following characteristics of a bacterium.

• Indole production - Positive - red color is observed.

This test is used for identifying the Enterobacteriaceae family members. A compound indole is produced due to the action of tryptophanase (organism) on tryptophan (in the medium).

• Methyl red - Positive - pink color is observed.

This is a differentiating test and identifying the bacteria that produce acid and the methyl red reagent added, indicates the acid production by giving out a red/pink color.

• VP/Vogues-Proskauer test - Negative - No color is observed

This is a differentiating test and identifying the bacteria that produce acetylmethylcarbinol via 2,3 butanediol fermentation. A negative test indicates that the organism uses a mixed acid production but not the 2,3- butanediol pathway.

• Citrate test - Negative - Green color was observed.

Citrate reagent is initially green in color and after the addition of bromothymol blue if there was citrate usage by the organism then it turns blue in color. But in this case, there is no change in the color and hence it is citrate negative.

• Gelatin hydrolysis - No liquefaction was observed.

Gelatin is a collagen-like compound and this test determines the ability of an organism to break down the gelatin by gelatinase enzyme. This test differentiates between the

• H₂S production - No production of hydrogen sulfide gas was observed.

This test signifies in identifying organisms that produce hydrogen sulfide gas when a sulfur-containing compound is provided in the medium. The results are interpreted by the observation of blackening of the medium.

• MacConkey medium - Good growth is observed. yellow color

This medium is a selective medium for the gram-negative enteric bacteria as the bile salts present in the medium inhibit the growth of gram-positive bacteria. An additional characteristic whether the organism can ferment the lactose fermentation. Yellow color observed indicates a lac negative organism which means that the organism is a gram-negative and lac negative.

The unknown organism is a gram-negative acid producing, doesn't produce hydrogen sulfide gas, does not utilize citrate, is indole positive. These characteristics bring us down to two options E.Coli and shigella except for the final test on Mac agar where the result is a non-lactose fermenting organism which is nothing but Shigella.