Prevalence and mechanisms of fosfomycin resistance among KPC-producing Klebsiella pneumoniae clinical isolates in China.

The threat of antibiotic resistance has increased dramatically in recent years. Fosfomycin, an old antibiotic agent, has been re-introduced to fight infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-KP). However, the trend of fosfomycin resistance among KPC-KP strains is increasing. In this study, 80 KPC-KP clinical isolates were collected from three teaching hospitals during 2014-2017 in China and were subjected to whole-genome sequencing (WGS). The fosfomycin resistance phenotype and resistance mechanisms were investigated by antimicrobial susceptibility testing and carbon source growth test, respectively. Among all KPC-KP strains, 80.0% (64/80) were resistant to fosfomycin and 36.3% (29/80) were positive for the mobile fosfomycin resistance gene fosA3. Among the 63 strains that were unable to grow in M9 basic medium with glycerol-3-phosphate (G3P) as the sole carbon source (mediated by mutation of the target gene glpT), there was no significant difference regarding the MIC distribution of fosfomycin between fosA3-positive and fosA3-negative strains (P = 0.577). Among the 50 strains that were negative for fosA3 but positive for fosA, the fosfomycin MICs of strains unable to grow in M9 basic medium with G3P as the sole carbon source were significantly higher (P < 0.001) than in strains that were able to grow in M9 basic medium with G3P as the sole carbon source. Our findings indicate that fosfomycin resistance among KPC-KP in China is an emerging problem and the two major mechanisms of resistance identified were plasmid-mediated fosfomycin resistance gene fosA3 and mutation of the target gene glpT.