ICAR AICE-JRF/SRF General Veterinary Microbiology: practice questions

Question 1 · hard

Gram-negative bacteria treated with lysozyme and EDTA in an isotonic sucrose solution become spherical but keep remnants of the outer membrane. Such forms are called:

1. Endospores
2. Mesosomes
3. Spheroplasts
4. Protoplasts

Question 2 · hard

In genome-based bacterial taxonomy, two isolates are usually regarded as the same species when their average nucleotide identity (ANI) is at least about:

1. 99.9%
2. 70%
3. 95-96%
4. 80%

Question 3 · hard

A food-poisoning organism with a generation time of 30 minutes is left in warm cooked food with an initial count of 10^2 CFU/g. Assuming no lag and unlimited exponential growth, about how long will it take to reach 10^8 CFU/g?

1. About 10 hours
2. About 7 hours
3. About 3 hours
4. About 20 hours

Question 4 · hard

In Bacillus species, sporulation is typically triggered when:

1. The culture is exposed to 121 degrees C
2. Cells enter the lag phase after inoculation into fresh medium rich in amino acids and sugars
3. Oxygen tension rises above atmospheric levels
4. Cells leave exponential growth and enter stationary phase as nutrients run out

Question 5 · medium

The genes for botulinum neurotoxin types C and D, and for Shiga toxins of Escherichia coli, are carried on bacteriophages. The acquisition of a new property by a bacterium through a prophage is called:

1. Phase variation
2. Transposition
3. Lysogenic conversion
4. Transformation (uptake of free DNA)

Question 6 · hard

The Sterne strain used in live anthrax spore vaccines is toxigenic but non-capsulated. Genetically this is because it:

1. Has a chromosomal mutation that inactivates lethal factor but leaves oedema factor and the capsule
2. Lacks both pXO1 and pXO2
3. Carries plasmid pXO1 (toxin genes) but lacks plasmid pXO2 (capsule genes)
4. Carries pXO2 (capsule genes) but lacks pXO1 (toxin genes)

Question 7 · hard

Class 1 integrons, common in Gram-negative bacteria from animals, are important in resistance spread because they:

1. Use an integrase to capture gene cassettes that are then expressed from a shared promoter
2. Encode a sex pilus for cell-to-cell transfer
3. Replicate independently of the chromosome as small circular DNA that carries its own origin
4. Are bacteriophages that inject resistance genes into every cell they infect in the gut

Question 8 · medium

In a heat-resistance test at 121 degrees C, the number of viable spores falls from 10^7 to 10^3 in 8 minutes. The D-value is:

1. 0.5 minutes
2. 2 minutes
3. 4 minutes
4. 8 minutes

Question 9 · hard

In a broth MBC test the starting inoculum is 5 x 10^5 CFU/mL. The MBC is defined as the lowest concentration that kills at least 99.9% of this inoculum. What is the highest surviving count allowed at the MBC?

1. 5,000 CFU/mL
2. 50,000 CFU/mL
3. 500 CFU/mL
4. 50 CFU/mL

Question 10 · hard

What is the main difference between an epidemiological cut-off value (ECOFF) and a clinical breakpoint?

1. An ECOFF is always higher than the clinical breakpoint, because it includes an extra safety margin for dosing
2. An ECOFF is used only for fungi
3. An ECOFF applies to disk diffusion and a breakpoint only to MIC tests
4. An ECOFF separates wild-type from acquired-resistance isolates; a breakpoint predicts treatment outcome