Characterization of clinical multidrug-resistant Escherichia coli and Klebsiella pneumoniae isolates, 2007-2009, China.

Various resistance mechanisms facilitate the emergence and spread of multidrug-resistance (MDR) phenotypes of Escherichia coli and Klebsiella pneumoniae. To elucidate the MDR mechanisms of E. coli and K. pneumoniae in China, we analyzed the antimicrobial susceptibilities of strains isolated from clinical samples in a large tertiary care hospital in Beijing, China, during 2007-2009 and characterized the isolates with a cefotaxime-ciprofloxacin-amikacin (CTX-CIP-AK) resistance pattern. In total, 98 and 52 clinical isolates of E. coli and K. pneumoniae, respectively, with a CTX-CIP-AK resistance pattern were subjected to antimicrobial susceptibility testing and screening of common β-lactamase genes, plasmid-mediated quinolone resistance (PMQR) genes, quinolone resistance-determining region (QRDR) substitutions, and 16S rRNA methylase genes by polymerase chain reaction amplification and DNA sequencing. Pulsed-field gel electrophoresis (PFGE) was used to determine the genetic relatedness of the isolates. Approximately 6.86% and 8.05% of the clinical E. coli and K. pneumoniae isolates, respectively, exhibited MDR phenotypes. The MDR K. pneumoniae isolates exhibited significantly higher ceftazidime resistance than the MDR E. coli isolates (90.4% vs. 76.5%, p=0.0339); a similar result was noted for piperacillin-tazobactam resistance (28.8% vs. 2%, p=0.0001). The common resistance determinants among the MDR E. coli and K. pneumoniae isolates were as follows: CTX-M (88.8% vs. 82.7%), PMQR genes (70.4% vs. 90.4%), gyrA mutations (100% vs. 90.4%), and 16S rRNA methylase genes (93.9% vs. 94.2%). Half (50%) of the MDR E. coli isolates belonged to phylogenetic group D, followed by group A (39.8%). For the E. coli isolates, 94 PFGE patterns and 23 clusters were identified, whereas 51 PFGE patterns and 11 clusters were identified for the K. pneumoniae isolates. Clinical E. coli and K. pneumoniae isolates seem to have a low prevalence of MDR phenotypes in China. The great genetic variation indicates a considerable transmission of common resistance determinants, including a high prevalence of QRDR substitutions in E. coli and K. pneumoniae.