TNPSC Animal Husbandry & Veterinary Science (Degree Standard), Code 396 · India · Tamil Nadu Public Service Commission
Original practice questions written to the published syllabus · not past papersHow bacteria and fungi are built, grown, identified and killed, and how bacteria become resistant to antimicrobials.
In the exams: ICAR AICE-JRF core group 06; ICAR AIEEA-PG 13 (Microbiology); PRC Microbiology & Public Health 14%; China microbiology and immunology 35 (its largest single component); TNPSC Micro/VPH/Preventive Medicine 30
How our questions for TNPSC Animal Husbandry & Veterinary Science, Code 396 spread across the units of General Veterinary Microbiology. Difficulty: 32 easy, 13 medium, 0 hard.
| Culture methods | 6 | |
| General mycology | 6 | |
| Bacterial structure | 5 | |
| Bacterial identification | 5 | |
| Sterilisation | 5 | |
| Disinfection | 5 | |
| Bacterial genetics | 4 | |
| Bacterial classification | 3 | |
| Bacterial growth | 3 | |
| Mechanisms of antimicrobial resistance | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which part of the Gram-negative lipopolysaccharide (LPS) is responsible for its endotoxic (pyrogenic, shock-inducing) activity?
D. Lipid A
Lipid A anchors LPS in the outer membrane and is the toxic moiety; it signals through Toll-like receptor 4. The O polysaccharide is the O (somatic) antigen used in serotyping, not the toxic part. Porins are proteins, not part of LPS.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
Taxonomy, as used in bacteriology, comprises:
C. Classification, nomenclature and identification
Taxonomy is the science of arranging organisms into groups (classification), naming them (nomenclature) and assigning an unknown isolate to a named group (identification). The other lists are laboratory or genetic processes.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
The correct order of the phases of a bacterial growth curve in a closed (batch) culture is:
B. Lag, exponential, stationary, death
Inoculated cells first adapt (lag), then divide at a constant rate (exponential), then growth equals death as nutrients run out and wastes build up (stationary), and finally viable numbers fall (death or decline).
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
Obligate anaerobes such as Clostridium species are killed by oxygen mainly because they:
B. Lack effective catalase and superoxide dismutase to remove toxic oxygen radicals
Oxygen metabolism produces superoxide and hydrogen peroxide. Aerobes and facultative anaerobes detoxify these with superoxide dismutase and catalase; obligate anaerobes largely lack them. Anaerobes do make ATP by fermentation, so the claim that they cannot make ATP by fermentation is backwards.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
On MacConkey agar, lactose-fermenting colonies such as Escherichia coli appear pink to red because:
C. Acid from lactose fermentation turns the neutral red indicator red
MacConkey agar is selective (bile salts and crystal violet inhibit most Gram-positive bacteria) and differential (lactose with neutral red). Fermenters lower the pH and turn pink-red; non-fermenters such as Salmonella and Proteus stay pale.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
The typical IMViC pattern of Escherichia coli is:
D. Indole +, methyl red +, Voges-Proskauer -, citrate -
E. coli: ++--. Klebsiella and Enterobacter are typically --++ (they make acetoin, detected by VP, and use citrate). Salmonella is usually -+-+, which is the fourth pattern here.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
The uptake of free (naked) DNA from the environment by a competent bacterial cell is called:
D. Transformation
Transformation = free DNA; transduction = DNA carried by a bacteriophage; conjugation = transfer through direct cell contact, usually via a sex pilus. Griffith's experiment with pneumococci first demonstrated transformation.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
Transfer of bacterial genes from one bacterium to another by a bacteriophage is called:
A. Transduction
In transduction a phage packages host DNA and injects it into the next host. Generalised transduction can move any gene; specialised transduction moves genes next to the prophage insertion site. Lysogeny is the state of a phage genome integrated as a prophage, not the transfer itself.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
A heat-labile antibiotic solution for a culture medium is best sterilised by:
A. Membrane filtration through a 0.22 micrometre filter
Filtration removes bacteria without heat. A 0.22 micrometre filter retains bacteria but not most viruses and not reliably mycoplasmas, so it is regarded as sterile filtration for bacteria only. Heat would destroy the antibiotic.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
The combination of a sulfonamide with trimethoprim is synergistic because the two drugs:
D. Block two successive enzymes in the same folate synthesis pathway
Sulfonamides compete with para-aminobenzoic acid at dihydropteroate synthase; trimethoprim inhibits bacterial dihydrofolate reductase further down the same pathway. The sequential blockade is often bactericidal where each alone is bacteriostatic.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
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