Free FMGE Microbiology questions

Explanation

Autoclaving uses saturated steam under pressure and is highly effective against vegetative organisms and spores. It is suitable for many heat- and moisture-stable materials.

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Staphylococcus aureus is classically catalase positive and coagulase positive. Coagulase helps distinguish it from common coagulase-negative staphylococci.

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Streptococcus pyogenes is a group A beta-hemolytic streptococcus and is PYR positive. Optochin sensitivity and bile solubility are associated with Streptococcus pneumoniae.

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C. difficile toxins glucosylate Rho GTPases, disrupting the cytoskeleton and tight-junction integrity. This contributes to colitis and pseudomembrane formation.

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Diphtheria toxin inactivates elongation factor-2 through ADP-ribosylation. This blocks protein synthesis and causes local as well as systemic toxicity.

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Cholera toxin ADP-ribosylates the Gs alpha subunit, causing persistent adenylate cyclase activation and increased intracellular cAMP. Chloride and water secretion then increase markedly.

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The lipid-rich mycobacterial cell wall contains abundant mycolic acids. These contribute to acid-fast staining characteristics and resistance to many environmental stresses.

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Nocardia are aerobic, branching filamentous bacteria that are weakly acid-fast because of mycolic acids in their cell walls. They can cause pulmonary and disseminated disease, especially in immunocompromised patients.

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IgM anti-HBc is a marker of recent acute HBV infection and may remain detectable during the window period when HBsAg has disappeared but anti-HBs is not yet measurable.

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Fourth-generation assays detect HIV antibodies together with p24 antigen. The antigen component becomes detectable earlier than antibodies and improves early screening sensitivity.

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Influenza A has a segmented RNA genome. Reassortment of segments between distinct strains can produce a major antigenic change known as antigenic shift.

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Negri bodies are eosinophilic cytoplasmic inclusions classically found in neurons in rabies. They are a traditional pathological clue rather than the sole basis of modern diagnosis.

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Candida albicans classically forms germ tubes when incubated in serum under appropriate conditions. This is a rapid presumptive identification method.

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Cryptococcus neoformans possesses a prominent polysaccharide capsule that impairs phagocytosis. Capsular antigen detection is also useful in diagnosis.

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Crescent or banana-shaped gametocytes are characteristic of P. falciparum. This morphology is a classic differentiating feature on peripheral smear.

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E. histolytica invades colonic mucosa and produces ulcers that extend into the submucosa, creating the classic flask-shaped appearance.

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Type I hypersensitivity involves allergen-induced cross-linking of IgE on mast cells and basophils. This triggers rapid mediator release.

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C3b coats microbial surfaces and promotes recognition by complement receptors on phagocytes. C5a is better known for chemotaxis and anaphylatoxin activity.

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MMR contains live attenuated viral strains. Live vaccines generally induce strong cellular and humoral immunity but are contraindicated in certain severely immunocompromised patients.

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Membrane filtration physically removes microorganisms from heat-sensitive liquids. It is used when heating would damage the product.