Distribution of metallo-β-lactamase genes among clinically isolated strains of Gram-negative-rods and nosocomial infection control

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The prevalence of strains producing metallo-β-lactamase among 207 high-level ceftazidime-resistant gram-negative rods (GNRs) was investigated. The strains were isolated in twelve general hospitals in Aichi Prefecture through March 2002 and March 2003. Disk diffusion method using sodium mercapto-acetic acid (SMA) revealed that 60 of them were metallo-β-lactamase producers. The prevalence increased 10.3% in 1997,23.0% in 2001 to 29.0% in this study, and the increase was remarkable among species other than Psudomonas aeruginosa and Serratia marcescens. PCR analysis confirmed that all of the 60 metallo-β-lactamase producing strains detected by SMA disk diffusion method carried the bla_<IMP-1> gene. In this study, SMA disk diffusion method proved useful in detecting metallo-β-lactamase producing at low cost.In one hospital Extended-spectrum-β-lactamases (ESBLs) producing 13 strains (9 Escherichia coli and 4 Klebsiella oxytoca) were isolated in the internal ward and neonatal intensive care unit (NICU). By pulsed field gel electrophresis (PFGE) each 6 of the 9 strains and each 3 of 4 strains showed the same restriction pattern.In another hospital 9 methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated in the intensive care unit (ICU). By PFGE 8 of 9 strains were showed the same genotype.