Horizontal Transfer of Erythromycin Resistance from Clostridium difficile to Butyrivibrio fibrisolvens

This study demonstrates for the first time the in vitro transfer of the erythromycin resistance gene erm(B) between two
obligate anaerobes, the human spore-forming pathogen Clostridium difficile and the rumen commensal Butyrivibrio
fibrisolvens, suggesting that this event might occur also in the natural environment.

Butyrivibrio fibrisolvens is one of the most abundant bacteria isolated from the rumen and has also been identified in
the human gastrointestinal tract (29). It is a small, motile, curved rod with tapered ends that analysis of both cell wall
structure and 16S rRNA gene sequences indicate it is gram positive (5), although it is currently classified as gram
negative. Previous studies demonstrated that some tetracycline resistance determinants could be transferred, under
laboratory conditions, from different rumen and human microorganisms to B. fibrisolvens (11, 15).

Antibiotic resistance genes commonly reside on transmissible plasmids or on other mobile genetic elements which
allow the horizontal transfer of these genes between strains, species, and even genera of the normal microflora as
well as between pathogens of human and animal origin (6, 18, 24). It is known that antibiotics used in human and
veterinary medicine may increase the selective pressure on bacterial populations, which could result in an increase of
resistant bacteria (4, 12). The human and animal gastrointestinal tract is a good environment for horizontal gene
transfer events (22).
Antimicrobial Agents and Chemotherapy, December 2005, p. 5142-5145, Vol. 49, No. 12