Question 1

Refer to the first image (DNase agar plate). Which organism is positive for DNase activity, and what is the biochemical basis for this result?

Accepted Answer

S. aureus; it produces DNase, which hydrolyzes DNA, resulting in a clear halo where methyl green is released.

Question 2

In the second image (nutrient gelatin stabs), tube A is liquid after cooling, while tube B remains solid. What does this indicate about the enzymatic activity of the organisms?

Accepted Answer

Tube A is positive for gelatinase; tube B is negative for gelatinase.

Question 3

A bacterium is inoculated into phenol red glucose broth. After incubation, the broth is yellow with a bubble in the Durham tube (see image 3b). What is the correct interpretation?

Accepted Answer

The organism ferments glucose with acid and gas production.

Question 4

In the fourth image (TSI slants), tube C shows a yellow butt, red slant, and black precipitate. What is the correct interpretation of these results?

Accepted Answer

Glucose fermentation, no lactose/sucrose fermentation, H2S production.

Question 5

Refer to the fifth image (TSI slants). Organism 2 shows a pink slant, black butt. What does this indicate about its metabolic capabilities?

Accepted Answer

It ferments glucose only, reverts to protein catabolism, and reduces sulfur.

Question 6

In the sixth image (litmus milk tubes), tube C is almost completely white. What does this result indicate?

Accepted Answer

Litmus reduction has occurred, indicating anaerobic metabolism.

Question 7

In the seventh image (Simmons citrate agar), the tube on the right is blue. What does this indicate about the organism?

Accepted Answer

The organism can utilize citrate as its sole carbon source, producing alkaline byproducts.

Question 8

In the eighth image (urease test), tube (c) is bright pink. What does this result indicate?

Accepted Answer

Rapid urease production, resulting in ammonia and alkaline pH.

Question 9

Refer to the ninth image (nitrate reduction test flowchart). If a tube turns red only after the addition of zinc and HCl, what is the correct interpretation?

Accepted Answer

The organism did not reduce nitrate; the result is negative for nitrate reductase.

Question 10

In the tenth and eleventh images (catalase test), what is the difference between the two results shown?

Accepted Answer

The first is catalase negative (no bubbles); the second is catalase positive (bubbles present).

Question 11

In the twelfth and thirteenth images (oxidase test), what does the appearance of a blue color indicate?

Accepted Answer

Presence of cytochrome c oxidase enzyme.

Question 12

In the fourteenth image (EnteroPluri test), what does a yellow color in the glucose compartment indicate?

Accepted Answer

Glucose fermentation with acid production.

Question 13

In the fifteenth image (EnteroPluri scoring), how is the code for each group of three tests determined?

Accepted Answer

By adding the values for positive tests in each triplet (1, 2, 4).

Question 14

In the sixteenth image (API 20E system), what does a blue color in the citrate compartment indicate?

Accepted Answer

Positive for citrate utilization.

Question 15

In the seventeenth image (API 20E scoring), what is the 7-digit code for a profile with positive reactions in tubes 1, 3, 6, 10, 14, 17, and 20?

Accepted Answer

7031645

Biochemical Identification of Bacteria: Hydrolytic Enzymes, Carbohydrate Utilization, and Multitest Systems

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