[Analysis of the antibiotic resistant gene in multidrug-resistant Enterobacter cloacae isolated at Showa University Hospital].

We analyzed the antibiotic resistant genes, metallo-beta-lactamase and extended-spectrum beta-lactamase (ESBL), in highly resistant Enterobacter cloacae isolated at Showa University Hospital from April to June 2008. Thirty eight strains of E. cloacae were isolated. Of these strains, 35 demonstrating resistant to either cefotaxime (Minimum inhibitory concentration: MIC > or = 32 microg/ml), ceftadizime (MIC > or = 16 microg/ml), or aztreonam (MIC > or = 16 microg/ml) were selected for the analysis. The strains were subjected to a Double-disk synergy test (DDST) using sodium mercaptoacetic acid (SMA) and ceftadizime. As a result, 7 strains showed an enlargement of inhibition zone diameter by SMA. Among 7 SMA responded strains, 6 strains carried the bla(IMP-1) or bla(IMP-11) gene. There were 2 strains sensitive to imipenem (MIC < 1 microg/ml) in SMA responded strains, and one carried bla(IMP-11) gene. ESBL genes were detected in 5 strains, bla(CTX-M3) gene from 3 strains, and bla(CTX-M14) gene from 2 strains. All of the ESBL harboring strains showed an enlargement of inhibition zone diameter in DDST using clavulanic acid and ceftadizime, cefotaxime, aztreonam or cefepime. Among 35 strains, one strain carried both bla(IMP-1) and bla(CTX-M3) genes. In addition to the AmpC beta-lactamase, increase of the E. cloacae strains carrying these resistant genes cause the complex antibiotic resistant patterns. Especially, strains carrying bla(IMP) gene, which exhibit low imipenem MIC value may be induced to be resistant strains under the existence of imipenem. Analysis of resistant genes would be a beneficial for the measure the spread of drug-resistant E. cloacae.