Abstract:

Objective: The aim of this study was to investigate the molecular characteristics of carbapenem-resistant Enterobacteria­ceae (CRE) isolates from a teaching hospital in Guangdong, China, during the period between January 2008 and December 2011. Methods: A total of 28 (0.9%) CRE isolates were collected among 3286 isolates. Antimicrobial susceptibility testing, Modified Hodge Test (MHT) and genotyping by pulsed-field gel electrophoresis were performed. Extended-spectrum β-lactamase (ESBL) and carbapenemase genes were detected using gene amplification and sequencing. Outer membrane porin (OMP) genes (OmpK35/OmpK36 for K. pneumoniae, OmpC/OmpF for E. cloacae were examined. Results: Seven (25.0%) isolates of the 28 carbapenem resistant Enterobacteriaceae had a positive MHT. PCR and sequenc­ing analysis revealed that 19 of the 28 isolates were molecularly confirmed to harbor ESBLs (15 isolates, 53.6%), AmpC (6 isolates, 21.4%), or IMP-4 (five isolates, 17.9%), and nine (32.1%) isolates of the 28 isolates possessed at least two different classes of β-lactamases. Specially, five (71.4%) of seven MHT-positive CRE isolates is due to the production of the carbapen­emase-encoding gene IMP-4. Almost all of the CRE isolates in the present study loss gene expressions of OmpK35 and/or OmpK36 in K. pneumoniae, OmpC and/or OmpF in E. cloacae, except for one K. pneumoniae. PFGE analysis demonstrated genomic variability. Conclusion: Carbapenem resistance in Enterobacteriaceae is due to the combined effect of β- lactamases with porin im­permeability caused by loss of OMPs observed in these organisms. To prevent both CRE transmission and infections has become significantly urgent public health objectives.

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