An R-plasmid (resistance plasmid) carrying blaZ (beta-lactamase), tetM, aacA, and ermB genes is transferred from a methicillin-susceptible S. aureus to a new clinical isolate during horizontal gene transfer. Which mechanism of transfer is most likely in the clinical S. aureus context?

• A Transformation — uptake of naked plasmid DNA from dead organisms
• B Transduction — bacteriophage-mediated transfer of plasmid DNA ✓
• C Conjugation — direct cell-to-cell contact through pilus-mediated DNA transfer
• D Transposition — movement of mobile genetic elements between chromosomes

Explanation

S. aureus is not naturally competent for transformation. Conjugation occurs in staphylococci but requires specific conjugative plasmids; large R-plasmids in S. aureus are typically transferred by transduction via specific bacteriophages (phage 80, phage 52A). Staphylococcal pathogenicity islands (SaPI), which carry virulence and resistance genes, are also mobilised by bacteriophages. Transposition refers to movement of insertion sequences/transposons within or between replicons in a single cell, not horizontal transfer between cells.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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