A researcher is performing whole genome sequencing of a multidrug-resistant Enterobacter cloacae isolate. She finds a resistance gene on a 100 kb self-transmissible plasmid with tra operon genes and ori region. This plasmid can transfer resistance to a sensitive strain via:

• A Transformation — competent cells take up naked plasmid DNA from the environment
• B Transduction — bacteriophage packages the plasmid and injects it into recipient cells
• C Conjugation — plasmid encodes a sex pilus (F pilus) and DNA mobilisation proteins for direct cell-to-cell DNA transfer ✓
• D Transposition — resistance gene inserts into host chromosome via transposases

Explanation

A self-transmissible plasmid containing the tra (transfer) operon and a replication origin (ori) is capable of conjugative transfer. The tra operon encodes the F pilus (sex pilus or conjugative pilus) which forms a tube-like connection between donor and recipient bacteria, and DNA relaxase/helicase proteins that nick and unwind the plasmid DNA. During conjugation, a single-stranded copy of the plasmid is transferred through the mating channel to the recipient. This is the primary mechanism of horizontal gene transfer for antibiotic resistance between Gram-negative bacteria. Transformation requires competent cells and naked DNA. Transduction requires bacteriophage as intermediary. Transposition moves genes within/between DNA molecules but is not a mechanism of intercellular transfer by itself.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.