β-Lactamase-encoding Genes of Multiple-drug-resistant Enterobacter cloacae

OBJECTIVE To investigate the β-lactamase-encoding genes of Enterobacter cloacae isolated in Beijing Chaoyang Hospital. METHODS Standard agar dilution method,improved three-dimensional tests,PCR amplification,gene cloning and DNA sequencings were performed in the 12 strains of E. cloacae resistant to many antibiotics. RESULTS Twelve strains of E. cloacae were multiple-drug-resistant and proved to produce AmpC β-lactamase and ESBLs by improved three-dimensional tests. DNA sequences of 9 strains of E. cloacae revealed ESBLs of SHV-2,SHV-12,CTX-M-3,CTX-M-14 and β-lactamase of TEM-1 and SHV-11. The other three strains produced unidentified enzymes with pI 7.89 and 8.0 which were inhibited by cloxacillin. The ampD gene sequencing results of 6 strains showed that there were amino acid substitutions in the carboxy-terminal of AmpD. CONCLUSIONS Twelve strains of E. cloacae produced AmpC β-lactamase and one or more types of ESBLs.