Veterinary Parasitology- ICAR JRF/SRF 2024

• Evaluation of Assertion and Reason:
• Assertion (A): Coxiella burnetii grows on embryonated eggs and not on blood agar.
• True. C. burnetii is an obligate intracellular bacterium that cannot replicate on standard cell-free enriched bacteriological agars like blood agar; it is routinely cultivated in living host cell cultures or the yolk sac of 5–7-day-old embryonated chicken eggs.
• Reason (R): Coxiella burnetii is an "energy parasite".
• False. Chlamydia species are the classic "energy parasites" because they lack genes for ATP generation and must import host ATP via an ATP/ADP translocase. In contrast, genome sequencing has demonstrated that C. burnetii encodes a complete TCA cycle and functional respiratory chain, synthesizing its own ATP.
• nalysis:
• ((A) is correct but (R) is not correct): Correct.

• Phase-Contrast Microscopy:
• Invented in 1934 by Dutch physicist Frits Zernike (awarded the Nobel Prize in Physics in 1953).
• Uses an annular diaphragm and a phase plate to convert small phase shifts in light passing through transparent living biological specimens into corresponding changes in amplitude (brightness), enabling clear visualization of unstained living cells, bacteria, and organelles.
• nalysis:
• (Frits Zernike): Correct.

Correct option: (2) Frits Zernike

• Photoautotrophy:
• Organisms that utilize solar radiant energy to synthesize organic compounds from inorganic carbon dioxide ($CO_2$):
• Oxygenic Photoautotrophs: Cyanobacteria, green algae, and higher plants (use $H_2O$ as electron donor, releasing $O_2$).
• Anoxygenic Photoautotrophs: Green sulfur/non-sulfur bacteria and Purple sulfur/non-sulfur bacteria (use $H_2S$ or organic molecules as electron donors, without generating $O_2$).
• Fungi are non-photosynthetic, heterotrophic chemoorganotrophs.
• nalysis:
• (Green bacteria, purple bacteria, cyanobacteria and algae): Correct list of photoautotrophs.

Correct option: (4) Green bacteria, purple bacteria, cyanobacteria and algae

• LPS Structure and Bacterial Virulence:
• Lipopolysaccharide (LPS) in Gram-negative bacteria consists of Lipid A, core oligosaccharide, and the terminal O-antigen polysaccharide side chains.
• Smooth ($S$) Wild-Type Strains: Possess full-length O-antigen chains that sterically hinder the membrane attack complex (MAC, C5b-9) of complement from accessing the outer membrane, conferring serum resistance.
• Rough ($R$) Mutants: Genetic defects in LPS biosynthesis result in truncated core polysaccharides lacking the O-antigen. Lacking this steric shield, rough salmonellae are highly serum sensitive, easily lysed by complement, and rapidly cleared by phagocytosis.
• nalysis:
• Both (A) and (R) are correct, and (R) provides the mechanical explanation for (A). Hence, Option 1 is correct.