What is the most probable reason for antibiotic resistance development in bacteria?
Answer: B
Antibiotic resistance develops through natural selection. When antibiotics kill susceptible bacteria, resistant strains (with pre-existing mutations or acquired resistance genes) survive and proliferate.
Q.2Hard
Which of the following is a characteristic of prions that distinguishes them from viruses?
Answer: B
Prions are infectious agents composed solely of misfolded proteins (PrPsc) without any nucleic acids. They cause diseases like Creutzfeldt-Jakob disease (CJD). Viruses require nucleic acids for replication.
Q.3Hard
In the context of viral evolution, what is antigenic drift?
Answer: B
Antigenic drift involves gradual accumulation of point mutations in viral genes (especially surface proteins), causing slight changes in viral characteristics. This is distinct from antigenic shift (reassortment in segmented viruses like influenza).
Q.4Hard
A viral infection shows symptoms of hemorrhagic fever with high mortality. Laboratory tests reveal negative-sense RNA and a helical capsid. Which family of viruses is most likely?
Answer: B
Filoviruses (Ebola, Marburg) cause hemorrhagic fevers, possess negative-sense RNA, and display characteristic helical/filamentous morphology with extreme pathogenicity.
Q.5Hard
A bacterium isolated from contaminated water shows resistance to multiple antibiotics and possesses a plasmid. Which method would effectively identify if the plasmid carries resistance genes?
Answer: A
PCR with specific primers targeting antibiotic resistance genes (like mecA, blaTEM) directly amplifies and identifies plasmid-encoded resistance. Other methods lack this molecular specificity.
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Q.6Hard
Which of the following accurately describes the replication cycle of a negative-sense RNA virus?
Answer: B
Negative-sense RNA viruses must first synthesize complementary positive-sense RNA using viral RNA-dependent RNA polymerase. This positive-sense RNA serves as mRNA and template for new negative-sense genomes.
Q.7Hard
A virus exhibits tropism exclusively for liver hepatocytes. Which viral component determines this tissue-specific infectivity?
Answer: C
Viral tropism is determined by complementary interactions between viral attachment proteins and specific cell surface receptors. Hepatitis B, C viruses demonstrate hepatocyte tropism through receptor-specific binding.
Q.8Hard
In 2024, which antimicrobial stewardship approach has been emphasized to combat carbapenem-resistant Enterobacteriaceae (CRE)?
Answer: B
Current stewardship guidelines recommend combination therapy (often with colistin or fosfomycin), strict infection control, and judicious carbapenem use to prevent further resistance escalation in CRE.
Q.9Hard
Which viral envelope protein in paramyxoviruses is responsible for hemagglutination and neuraminidase activity?
Answer: B
The HN protein of paramyxoviruses mediates both hemagglutination (receptor binding) and neuraminidase activity (sialic acid cleavage), unlike orthomyxoviruses with separate H and N proteins.
Q.10Hard
A nosocomial infection outbreak is linked to environmental contamination by Acinetobacter baumannii. Which characteristic makes this organism particularly difficult to eradicate?
Answer: A
Acinetobacter baumannii forms robust biofilms on environmental surfaces and medical devices, surviving desiccation and disinfection, complicating infection control.
Q.11Hard
In viral uncoating mechanisms, which class of enveloped viruses releases their genome directly into the cytoplasm following fusion with endosomal membrane?
Answer: D
Multiple enveloped virus families (orthomyxoviruses, paramyxoviruses, alphaviruses) utilize pH-dependent endosomal fusion for genome release into cytoplasm.
Q.12Hard
Which bacterial species is an obligate intracellular pathogen that causes Q fever?
Answer: A
Coxiella burnetii is highly infectious, forms spores, and is transmitted through aerosol route from infected animals.
Q.13Hard
A patient with recurrent respiratory infections is found to have defective viral interferon response. Which immune component is primarily affected?
Answer: A
Type I interferons (IFN-α/β) are crucial for antiviral immunity; defects impair early viral containment.
Q.14Hard
Which mechanism allows certain bacteria to survive within macrophages despite phagocytosis?
Answer: A
Mycobacterium tuberculosis inhibits phagolysosome maturation and produces catalase to neutralize reactive oxygen species.
Q.15Hard
In the context of emerging infectious diseases 2024-25, which coronavirus variant has shown increased immune evasion?
Answer: A
Recent variants like XEC demonstrate accumulated mutations in the receptor binding domain conferring immune escape properties.
Q.16Hard
A research team identifies a novel coronavirus variant with enhanced spike protein binding affinity. Which cellular component would be most affected?
Answer: A
Increased spike protein affinity would enhance binding to ACE2 receptors, improving viral attachment and entry efficiency, particularly relevant to emerging variants.
Q.17Hard
Which bacterial defense mechanism specifically targets and degrades invading foreign DNA through restriction endonucleases?
Answer: B
Restriction-modification systems use restriction endonucleases to cut foreign DNA at specific recognition sites while protecting host DNA through methylation.
Q.18Hard
In coronavirus infection, the protease 3CL^pro cleaves the viral polyprotein. Which characteristic makes this enzyme an ideal drug target?
Answer: D
3CL^pro is highly conserved, essential for viral maturation, and structurally distinct from human enzymes, making it an excellent target for antivirals like nirmatrelvir.
Q.19Hard
Which bacterial mechanism explains how Neisseria gonorrhoeae evades the immune system through antigenic variation?
Answer: B
N. gonorrhoeae uses gene conversion to shuffle silent pili gene segments, creating new surface antigens faster than immune response, enabling chronic infection.
Q.20Hard
A diagnostic laboratory detects elevated interferon-gamma levels in response to viral infection. This indicates activation of which immune cell type?
Answer: B
CD8+ cytotoxic T lymphocytes produce IFN-γ upon encountering virus-infected cells presenting viral antigens on MHC-I, indicating cellular immune response activation.
