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NEET-PG 2014 — Microbiology

Q: Major bacterial enzyme responsible for putrefaction:

Protease. ***Protease*** - **Proteases** break down **proteins** into smaller peptides and amino acids, a key process in **putrefaction** (decomposition of organic matter by microorganisms). - Bacterial proteases are essential for the degradation of **tissue proteins** post-mortem, contributing to the characteristic odor and liquefaction of decaying bodies. *Metalloproteinase* - **Metalloproteinases** are a specific class of proteases that require a **metal ion** (usually zinc) for their catalytic activity. - While they contribute to protein degradation, the general term **protease** encompasses all enzymes involved in protein breakdown during putrefaction, making it a broader and more accurate answer. *Hyaluronidase* - **Hyaluronidase** breaks down **hyaluronic acid**, a main component of the **extracellular matrix**, aiding in bacterial invasion and spread. - Its primary role is in **tissue penetration** rather than the bulk decomposition of proteins characteristic of putrefaction. *Collagenase* - **Collagenase** specifically targets **collagen**, the most abundant protein in the body, breaking it down into smaller peptides. - While important for degrading a major structural protein, it is a specific type of protease, and the general term **protease** better describes the overall enzymatic activity responsible for putrefaction. [Practice more Microbiology PYQs on OnCourse]

Q: All tests are used to detect live bacteria, except:

ELISA for antibodies. ***Correct: ELISA for antibodies*** - **ELISA (Enzyme-linked immunosorbent assay)** for antibodies detects the **host's immune response** to an infection, not the bacteria themselves - This test identifies **antibodies** (IgM, IgG, IgA) produced by the immune system in response to bacterial antigens - **Does NOT detect bacteria** (live or dead) - it detects the immunological memory of exposure - Antibody presence indicates past or current exposure but tells us nothing about the presence of live organisms *Incorrect: Gram staining* - **Gram staining** is primarily a **morphological identification tool** that visualizes bacteria under microscopy - While it stains both live and dead bacteria equally, it is **used clinically to detect bacteria in specimens** (CSF, pus, sputum) - In the context of bacterial detection methods, seeing bacteria on Gram stain from a clinical specimen indicates bacterial presence and guides immediate therapy - Though not a specific viability test, it demonstrates bacterial presence in the sample being examined *Incorrect: Blood culture* - **Blood culture** involves inoculating blood into growth media and incubating to allow bacterial multiplication - **Only viable (live) bacteria will grow** in culture media - this is the gold standard for detecting live bacteria in bloodstream infections - Growth in culture definitively confirms the presence of living, metabolically active bacteria *Incorrect: Direct microscopy with vital stains* - **Vital stains** (e.g., acridine orange, fluorescein diacetate) are dyes that differentiate living cells from dead cells - These stains rely on **metabolic activity** or **intact cell membrane** to distinguish viable organisms - Used in direct microscopy to specifically identify **live bacteria** based on their ability to take up or exclude certain dyes [Practice more Microbiology PYQs on OnCourse]

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Major bacterial enzyme responsible for putrefaction:

All tests are used to detect live bacteria, except: