During investigation of a hospital outbreak of vancomycin-resistant Enterococcus faecium, isolates from several wards require comparison at the strain level. Which method is regarded as the reference standard for such molecular epidemiological typing?

• A Antibiogram comparison across all isolates
• B Serotyping with pooled antisera
• C Pulsed-field gel electrophoresis of macrorestriction fragments ✓
• D Colony morphology on selective media

Explanation

Pulsed-field gel electrophoresis digests genomic DNA with rare-cutting restriction enzymes and resolves large macrorestriction fragments under alternating electric fields, giving highly discriminatory banding patterns that define clonal relationships. Antibiograms and colony morphology lack discriminatory power, and many hospital pathogens such as enterococci have limited serotypable antigens, making phenotypic methods unreliable for establishing a common source.

Reference: Bailey and Scott's Diagnostic Microbiology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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