A laboratory isolate of Corynebacterium diphtheriae is initially non-toxigenic by the Elek test. After infection with bacteriophage beta, the organism begins producing diphtheria toxin and becomes Elek positive. The progeny bacteria continue to produce toxin through many generations even when the phage is not replicating lytically. The phenomenon responsible is:

• A Generalised transduction
• B Transformation with naked phage DNA
• C Lysogenic (phage-mediated) conversion ✓
• D Spontaneous point mutation in the tox locus

Explanation

Lysogenic conversion occurs when a temperate phage genome integrates into the bacterial chromosome and a phage-borne gene confers a new phenotype on the host, expressed as long as the prophage persists. The diphtheria tox gene resides on the beta phage genome, so only lysogenised corynebacteria produce toxin. Spontaneous mutation cannot explain stable acquisition of a whole toxin structural gene, and transduction would require packaging of chromosomal rather than phage DNA.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.