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

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Macrolide-lincosamide-streptogramin B resistance in Clostridium difficile is primarily mediated by erm(B) genes.
• Tn6194, a conjugative transposon harboring erm(B), has been found in various C. difficile PCR-ribotypes, including the prevalent PCR-ribotype 027.
• Understanding the transmission dynamics of antibiotic resistance elements is crucial for combating bacterial infections.

Purpose of the Study:

• To characterize a novel erm(B)-containing conjugative transposon in Clostridium difficile PCR-ribotype 001.
• To investigate the transferability and integration of this element into other C. difficile strains and Enterococcus faecalis.
• To provide molecular insights into antibiotic resistance gene dissemination in the human gut microbiome.

Main Methods:

• Genome sequencing of a C. difficile PCR-ribotype 001 strain to identify the novel element.
• Filter mating assays to transfer the element to recipient C. difficile (PCR-ribotypes 009, 027) and Enterococcus faecalis strains.
• Southern blotting and genome sequencing of transconjugants to confirm transfer and identify integration sites.

Main Results:

• A novel conjugative transposon, similar to Tn6194 but with two nucleotide changes, was identified in C. difficile PCR-ribotype 001.
• The element successfully transferred to and integrated into the genomes of recipient C. difficile strains at diverse locations.
• The transposon also integrated into the Enterococcus faecalis genome at a specific site, demonstrating interspecies transferability.
• This marks the first molecular characterization of an erm(B)-carrying conjugative transposon in C. difficile.

Conclusions:

• The identified element represents a significant mechanism for the spread of macrolide-lincosamide-streptogramin B resistance in C. difficile.
• The ability of this transposon to transfer between different C. difficile PCR-ribotypes and to E. faecalis highlights the risk of antibiotic resistance gene transmission.
• This finding underscores the potential for horizontal gene transfer among bacteria sharing the same ecological niche, such as the human intestinal tract.