Occurrence and analysis of rare cfiA–bft doubly positive Bacteroides fragilis strains

• 4 cfiA and bft-positive B. fragilis strains were detected among 486 B. fragilis strains from Europe.
• The prevalences of the bft genes were the same in cfiA-negative and -positive strains.
• The bft–cfiA double positive strains belonged to the I.1. genomic pattern.
• We inferred that the bft-carrying conjugative transposons are really mobile.

We detected four cfiA–bft1 doubly positive Bacteroides fragilis strains out of 486 B. fragilis isolates analyzed for antibiotic susceptibilities and antibiotic resistance genes from a recent pan-European survey. The prevalence of the enterotoxin bft genes was roughly equal among cfiA-negative and -positive B. fragilis strains. We also demonstrated that the cfiA–bft doubly positive strains had the most common B. fragilis genomic pattern (I.1.). Thus we concluded that the bft-carrying CTn86 conjugative transposons are mobile accounting for this unexpected simultaneous occurrence of the cfiA and bft genes.