Plasmid mediated fosfomycin resistance and its mechanism in extended-spectrum β-lactamases producing Klebsiella pneumonia

Abstract

Objective To investigate the fosfomycin resistance and its mechanism in extended-spectrum β-lactamases (ESBL) producing Klebsiellapneumoniae (K. pneumoniae) from clinical samples. Methods Seventy-nine isolates of ESBL-producing clinical K. pneumoniae were collected at Sir Run Run Shaw Hospital, Zhenjiang University School of Medicine from July 2014 to December 2014. Minimal inhibitory concentration (MIC) of fosfomycin was determined by the agar dilution method, and the susceptibility breakpoint was interpreted as ≤32 mg/L according to European Committee on Antimicrobial Susceptibility Testing (EUCAST). Phylogenetic clonal patterns were analyzed by pulse-field gel electrophoresis (PFGE), and plasmid size and similarity were revealed by nuclease assay. Filter membrane conjugation assay was carried out for determination of resistance transfer by plasmid. All the isolates were screened for plasmid-mediated fosfomycin resistance genes by polymerase chain reaction (PCR) amplification, and the structures of up- and down-stream resistance genes were analyzed. Results Nine of 79 isolates of ESBL-producers were resistant against fosfomycin, and the resistance rate was 11.4%. PFGE and S1-PFGE revealed that all the 9 fosA3-harboring isolates were not clone related and not plasmid similar. All of the 9 resistant isolates were fosA3 positive, which was one of the plasmid mediated fosfomycin resistance genes. No other fosA or fosC2-positive resistant genes were found. fosA3 gene coded by resistant isolates was found to be flanked by two copies of IS26. Conclusions Fosfomycin resistant isolates are emerged in ESBL-producing clinical K. pneumoniae. Producing fosfomycin-modifying enzyme fosA3 coded by plasmid is the major mechanism in fosfomycin resistant isolates. The IS26 element accelerates the resistance genes dissemination. Key words: Klebsiella pneumoniae; Fosfomycin; Resistance; Plasmids