Fosfomycin resistance among vancomycin-resistant enterococci owing to transfer of a plasmid harbouring the fosB gene.

The presence and characterisation of plasmid-mediated fosfomycin resistance determinants were investigated among 45 clinical vancomycin-resistant enterococci (VRE) isolated in Zhejiang Province, China. In total, 19 VRE were resistant to fosfomycin, of which 18 isolates had conjugative fosfomycin resistance and were positive for fosB. No reported fos genes were detected in the remaining isolate. Among the 18 fosB-carrying isolates, the fosB gene was always flanked by tnpA, suggesting the same novel fosB transposon. In 10 of the 18 fosB-carrying isolates, the fosB and tnpA genes were found reversely inserted in the vanA transposon Tn1546. In the remaining eight isolates the fosB and vanA genes were located on different plasmids. These findings indicate that acquisition of the conjugative plasmid harbouring the novel fosB transposon (ISL3-like transposon) and the Tn1546-like transposon (containing vanA and fosB) may explain, at least in part, the recent increase in fosfomycin-resistant Enterococcus faecium in China.