Question

1. the citrate test determines whether a bacterium can:

a) produce gas from glucose fermentation
b) utilize citrate as the sole carbon source
c) hydrolyze gelatin
d) deaminate phenylalanine

1. a blue color on a simmons citrate slant indicates:

a) neutral ph
b) acidic conditions due to glucose fermentation
c) alkaline conditions due to ammonia production
d) the presence of indole

1. which two imvic tests are typically positive for enterobacter aerogenes and negative for e. coli?

a) indole and methyl red
b) voges-proskauer and citrate
c) methyl red and voges-proskauer
d) indole and citrate

Explanation:

• Question 5: The citrate test is designed to check if a bacterium can use citrate as the only carbon source. Glucose fermentation gas production is tested by other methods (e.g., Durham tube in fermentation tests), gelatin hydrolysis is for the gelatinase test, and deamination of phenylalanine is for the phenylalanine deaminase test.
• Question 6: In Simmons citrate agar, when bacteria utilize citrate, they produce alkaline by - products (like ammonia from ammonium salts). The pH indicator (bromthymol blue) turns blue in alkaline conditions. Neutral pH would not cause this color change, acidic conditions (from glucose fermentation, which is not the case here as citrate is the carbon source) would make it yellow, and indole presence is tested by other methods (e.g., Kovac's reagent in indole test).
• Question 7: Enterobacter aerogenes is typically positive for Voges - Proskauer (produces acetoin) and Citrate (can utilize citrate) tests. E. coli is negative for these two tests. E. coli is positive for Indole (due to tryptophanase activity) and Methyl Red (produces mixed acids), while Enterobacter aerogenes is negative for these two.

Answer:

1. B. Utilize citrate as the sole carbon source
2. C. Alkaline conditions due to ammonia production
3. B. Voges - Proskauer and Citrate