Molecular analysis of chromosomally florfenicol-resistant Escherichia coli isolates from France and Germany

The aim of this study was to analyse chromosomally florfenicol-resistant Escherichia coli isolates for their genetic relatedness, and also for the presence of the floR gene and its adjacent regions, in order to compare these regions with those associated with a floR gene located on a conjugative plasmid from E. coli. Twenty-two bovine E. coli from France and Germany were examined. Florfenicol resistance was determined by MIC determination. The presence of the floR gene was confirmed by hybridization and PCR analysis. The E. coli isolates were investigated by macrorestriction analysis. The 22 florfenicol-resistant E. coli (MICs 64-->128 mg/L) differed in their BlnI macrorestriction patterns. Single or double copies of the floR gene were detected by hybridization on different-sized chromosomal EcoRI, BamHI and BglI fragments. The floR-flanking regions also proved to be variable as confirmed by hybridization experiments. The detection of chromosomal floR gene copies in unrelated E. coli isolates supplements the observations of floR genes on plasmids in E. coli and confirms their potential to integrate into the chromosome. The RFLPs of floR gene-carrying restriction fragments might suggest variable chromosomal integration sites.