Question 1

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]

Question

All tests are used to detect live bacteria, except:

Accepted Answer

ELISA for antibodies

Answer

Gram staining

Answer

Blood culture

Answer

Direct microscopy with vital stains

NEET-PG 2014 — Microbiology