Phenotypic and Molecular Characteristics of Carbapenem-Non-Susceptible Enterobacteriaceae from a Teaching Hospital in Wenzhou, Southern China

Carbapenem resistance in Enterobacteriaceae is increasing and has become a matter of great concern. The aim of this study was to characterize carbapenem-non-susceptible Enterobacteriaceae from a teaching hospital. A total of 49 carbapenem-non-susceptible Enterobacteriaceae clinical isolates recovered in 2007-2010 from the First Affiliated Hospital of Wenzhou Medical College were analyzed by antimicrobial susceptibility testing. The carbapenemase phenotype, outer membrane protein profiles, and clonal relatedness were investigated using the modified Hodge test, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and pulsed-field gel electrophoresis (PFGE). Multilocus sequence typing (MLST) of Klebsiella pneumoniae was also performed. beta-Lactamase genes were examined by PCR and sequencing, and the transferability of carbapenemase genes was determined by a conjugation experiment. The rates of imipenem, meropenem, and ertapenem resistance were 59.2%, 40.8%, and 96.0%, respectively. Thirty isolates exhibited carbapenemase activity, and 32 isolates carried carbapenemase genes. Furthermore, 10 and 9 clinical isolates posessed AmpC beta-lactamase and extended-spectrum beta-lactamase (ESBL) genes, respectively. Eight of 32 carbapenemase-producing isolates were proved to be carried by conjugative plasmids, and there was porin loss in 34.7% (17/49) of the isolates. PFGE analysis demonstrated that 9 KPC-2-producing Serratia marcescens belonged to a clonal strain, suggesting the clonal dissemination of these KPC-2-bearing isolates among different wards. The MLST of K. pneumoniae revealed that two KPC-2 producers were ST11. This study suggests that KPC-2-type carbapenemase is the main contributor to carbapenems resistance in carbapenemase-producing Enterobacteriaceae, and that ESBL, AmpC beta-lactamase overproduction, and porin loss contribute to the resistance level among these isolates; in carbapenemase-non-producing Enterobacteriaceae, ESBL, AmpC enzyme, and porin loss contribute to the carbapenems resistance of Enterobacteriaceae, especially the ertapenem resistance of Enterobacter cloacae.