First Report in China of Enterobacteriaceae Clinical Isolates Coharboring blaNDM-1 and blaIMP-4 Drug Resistance Genes

Aims: To describe the identification of two carbapenem-resistant, NDM-1 and IMP-4, carbapenemases coproducing Enterobacteriaceae isolates recovered from hospitalized patients in China. Both Klebsiella pneumoniae clinical isolates (Kpn922 and Kpn9599) were resistant to meropenem and imipenem and were subjected to additional antibiotic susceptibility testing. Polymerase chain reaction (PCR) and sequence analyses were used to characterize bacterial carbapenemase resistance genes, extended-spectrum beta-lactamases, plasmid-mediated AmpC enzymes, quinolone resistance, and 16s RNA methylase. Genetic relatedness was determined using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Plasmids were analyzed by S1-PFGE and Southern blot. Results: PCR analyses revealed that the Kpn922 isolate carried bla(NDM-1), bla(IMP-4), bla(TEM-1), and bla(SHV-1) genes, while Kpn9599 carried bla(NDM-1), bla(IMP-4), bla(TEM-1), and bla(SHV-12) genes. MLST determined that the two isolates were ST1043 and ST571 sequence types. Southern blot analyses revealed that metallo-beta-lactamase genes were plasmid borne in both isolates. Plasmids similar to 300 kb simultaneously carried bla(NDM-1) and bla(IMP-4). Conclusions: Coexistence of bla(NDM-1) and bla(IMP-4) in these clinical isolates may herald the emergence of a new pattern of drug resistance. Surveillance of carbapenemases, particularly metallo-beta-lactamases, in Enterobacteriaceae is urgently needed to control and prevent the spread of these resistance determinants in China.