Inter- and intraspecies transfer of a Clostridium difficile conjugative transposon conferring resistance to MLSB

Abstract

Resistance to the macrolide-lincosamide-streptogramin B group of antibiotics in Clostridium difficile is generally due to erm(B) genes. Tn6194, a conjugative transposon initially detected in PCR-ribotype 027 isolates, is an erm(B)-containing element also detected in other relevant C. difficile PCR-ribotypes. In this study, the genome of a C. difficile PCR-ribotype 001 strain was sequenced, and an element with two nucleotidic changes compared to Tn6194 was detected. This element was transferred by filter mating assays to recipient strains of C. difficile belonging to PCR-ribotype 009 and 027 and to a recipient strain of Enterococcus faecalis. Transconjugants were characterized by Southern blotting and genome sequencing, and integration sites in all transconjugants were identified. The element integrated the genome of C. difficile at different sites and the genome of E. faecalis at a unique site. This study is the first molecular characterization of an erm(B)-containing conjugative transposon in C. difficile and provides additional evidence of the antibiotic resistance transmission risk among pathogenic bacteria occupying the same human intestinal niche.