Molecular Epidemiology of Plasmid-Mediated Fosfomycin Resistance Gene Determinants in Klebsiella pneumoniae Carbapenemase-Producing Klebsiella pneumoniae Isolates in China.

The Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae has become a serious problem because the species is wide ranging and there are few treatment options. Fosfomycin has attracted renewed interest in combination therapy for infections caused by KPC-producing K. pneumoniae isolates. Because of the increasing use of fosfomycin, resistant isolates have been continually reported in carbapenem-resistant K. pneumoniae (CRKP). At present, multiple mechanisms can result in fosfomycin resistance. However, there is limited knowledge with respect to plasmid-mediated fosfomycin resistance gene (fosA3) determinants in KPC-producing K. pneumoniae isolates. In this study, a total of 101 CRKP strains were collected from four hospitals in Zhejiang province from January 2013 to August 2014; 28.7% (29/101) of CRKP isolates were resistant to fosfomycin. Gene fosA3 was detected in 29 fosfomycin-resistant KPC-producing K. pneumoniae isolates, whereas genes fosA, fosB, fosB2, fosC, fosC2, and fosX were all negative among the resistant isolates. In addition, among 29 fosfomycin-resistant KPC-producing K. pneumoniae isolates, pulsed-field gel electrophoresis (PFGE) analysis revealed five pulsotypes. S1-PFGE and Southern blot showed that the fosA3 gene was located on an approximately 140-kb plasmid in all isolates. Eight of the 29 isolates (27.6%) tested could successfully transfer their fosfomycin-resistant phenotype to Escherichia coli strain J53. All fosA3-positive isolates were determined to have an identical genetic background, IS26-tetR-cadC-orf1-fosA3-IS26, which is the same as that of the fosA3-positive plasmid pFOS18 in China. The primary resistance mechanism to fosfomycin was caused by a plasmid-mediated fosA3. Furthermore, it is noteworthy that the plasmid genetically carrying a combination of the fosA3 and bla(KPC-2) genes could accelerate the spread of antibiotic resistance. Effective and persistent monitoring and surveillance will be vital to prevent further dissemination of these resistance genes.