Transmission and characterization of bla NDM-1 in Enterobacter cloacae at a teaching hospital in Yunnan, China.

BACKGROUND: In recent years, New Delhi metallo-beta-lactamases 1 (bla NDM-1) has been reported with increasing frequency and become prevalent. The present study was undertaken to investigate the epidemiological dissemination of the bla NDM-1 gene in Enterobacter cloacae isolates at a teaching hospital in Yunnan, China.

METHODS: Antimicrobial susceptibility testing was performed using VITEK 2 system and E test gradient strips. The presence of integrons and insertion sequence common region 1 were examined by PCR and sequencing. Clonal relatedness was assessed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Conjugation experiments and Southern blot hybridization were performed to determine the transferability of plasmids.

RESULTS: Ten E. cloacae isolates and their Escherichia coli transconjugants were exhibited similar resistant patterns to carbapenems, cephalosporins and penicillins. 8 (80%) of E. cloacae isolates carried class 1 integron and 1 (12.5%) carried class 2 integron. Integron variable regions harbored the genes which encoded resistance to aminoglycosides (aadA1, aadA2, aadA5, aadB, aac(6')-Ib-cr), sulfamethoxazole/trimethoprim (dfrA17, dfrA12, dfrA15) and Streptozotocin (sat2). Six E. cloacae isolates belonged to ST74 and exhibited highly similar PFGE patterns. Each isolate shared an identical plasmid with ~33.3 kb size that carried the bla NDM-1 gene, except T3 strain, of which the bla NDM-1 gene was located on a ~50 kb plasmid.

CONCLUSIONS: Our findings suggested that plasmid was able to contribute to the dissemination of bla NDM-1. Hence, more attention should be devoted to monitor the dissemination of the bla NDM-1 gene due to its horizontal transfer via plasmid. In addition, nosocomial surveillance system should actively monitor the potential endemic clone of ST74 to prevent their further spread.