High prevalence of fosfomycin resistance gene fosA3 in bla_CTX-M-harbouring Escherichia coli from urine in a Chinese tertiary hospital during 2010-2014

Fosfomycin has become a therapeutic option in urinary tract infections. We identified 57 fosfomycin-resistant Escherichia coli from 465 urine-derived extended-spectrum β-lactamase (ESBL)-producing isolates from a Chinese hospital during 2010-2014. Of the 57 fosfomycin-resistant isolates, 51 (89.5%) carried fosA3, and one carried fosA1. Divergent pulsed-field gel electrophoresis profiles and multi-locus sequence typing results revealed high clonal diversity in the fosA3-positive isolates. Conjugation experiments showed that the fosA3 genes from 50 isolates were transferable, with IncFII or IncI1 being the most prevalent types of plasmids. The high prevalence of fosA3 was closely associated with that of bla_CTX-M. Horizontal transfer, rather than clonal expansion, might play a central role in dissemination. Such strains may constitute an important reservoir of fosA3 and bla_CTX-M, which may well be readily disseminated to other potential human pathogens. Since most ESBL-producing E. coli have acquired resistance to fluoroquinolones worldwide, further spread of fosA3 in such E. coli isolates should be monitored closely.