Microbiological Characteristics of Carbapenem-Resistant Enterobacteriaceae Clinical Isolates Collected from County Hospitals

To investigate the molecular characteristics of carbapenem-resistant Enterobacteriaceae (CRE) from county hospitals in China.

Forty-three sequential non-duplicate CRE strains (including 33 Klebsiella pneumoniae isolates, 4 Enterobacter cloacae isolates, 3 Escherichia coli isolates, 1 Serratia marcescens, 1 Morganella morganii and 1 Citrobacter freundii) were collected from 4 county hospitals and 2 municipal hospitals. Antimicrobial susceptibility testing was conducted by broth microdilution method, using 3-aminophenylboronic acid and EDTA and the modified carbapenem inactivation method (mCIM) to screen phenotype of carbapenemase. β-Lactamases were characterized by polymerase chain reaction (PCR) and DNA sequencing. The transferability of bla _NDM-5 was investigated by transformation experiment. Clonal relatedness was evaluated by pulsed-field gel electrophoresis and multilocus sequence typing .

The results of antimicrobial susceptibility testing indicated that 43 CRE strains were resistant to most of the antimicrobial agents, except tigecycline and colistin. Overall, 93%, 93%, and 97.7% of these strains were resistant to imipenem, meropenem, and ertapenem, respectively. PCR and DNA sequencing indicated that 67.4% (29/43) were bla _KPC-2 positive isolates, in which 3.4% (1/29) was coproduced with bla _NDM-1. In addition, 7.0% (3/43), 4.7% (2/43), 4.7% (2/43), 2.3% (1/43), 2.3% (1/43) were bla _NDM-1, bla _NDM-16, bla _NDM-4, bla _NDM-5, bla _IMP-4 positive isolates, respectively. The 29 bla _KPC-2-positive isolates belonged to 12 different PFGE type and designated as ST11 (n=20) and ST15, ST39, ST116, ST667, ST2245, ST2338. The plasmid bearing bla _NDM-5 could be transferred into recipient E. coli J53 through transformation.

Our study indicated the dissemination of CRE between the tertiary hospitals and secondary hospitals.