Q73. Which of the following method(s) can be applied to identify a bacterial
species?
(A) Fluorescent in situ hybridization (FISH)
(B) Polymerase chain reaction (PCR) followed by sequencing of the amplicon
(C) Gram staining
(D) Acid–fast staining
PCR followed by sequencing and Fluorescent in situ hybridization (FISH) provide precise bacterial species identification through genetic analysis. Gram staining and acid-fast staining classify bacteria into broad groups but fall short for species-level distinction. All options except (C) and (D) enable accurate species identification, making (A) and (B) correct.
Option Analysis
Fluorescent in situ hybridization (FISH):
FISH uses fluorescent probes targeting specific rRNA sequences to bind and visualize intact bacterial cells, enabling species-level identification without cultivation. Probes designed for 16S rRNA variations distinguish species like those in bacteremia with 96-99.9% accuracy. This method suits environmental and clinical samples for rapid, in situ detection.
PCR followed by sequencing:
PCR amplifies conserved regions like 16S rRNA genes, and sequencing analyzes variable sequences for precise species matching against databases. This gold standard identifies unculturable bacteria and achieves high sensitivity down to 1-10 CFU. It outperforms phenotypic methods in diagnostics.
Gram staining:
Gram staining differentiates Gram-positive (purple) from Gram-negative (pink) bacteria based on cell wall peptidoglycan thickness. It aids initial grouping and morphology observation but cannot resolve species within groups.
Acid-fast staining:
Acid-fast staining detects waxy mycolic acid in cell walls, identifying acid-fast (red) versus non-acid-fast (blue) bacteria like Mycobacterium species. It specifies genera but not individual species reliably.
Correct Answer
(A) and (B)
