Detection of the BlaIMP-1 ^|^beta;-Lactamase Gene in Clinically Isolated Cefotaxime-Resistant Strains of Serratia Marcescens, Klebsiella Pneumoniae, and Enterobacter Cloacae

We analyzed cefotaxime-resistant Gram-negative bacillus isolated at Showa University Hospital between October 1996 and September 1998 for strains producing extended-spectrum β-lactamase. By measurement of the minimum inhibitory concentration (MIC) of cefotaxime, 51 strains out of 579 isolates of Serratia marcescens (S. marcescens), 4 strains out of 1756 isolates of Klebsiella pneumoniae (K. Pneumoniae), and 2 strains out of 1007 isolates of Enterobacter cloacae (E. cloacae) were identified as cefotaxime resistant. The MIC measurement at high concentrations of Ampicillin, Ceftazidime, Cefmetazole, Cefaloridine, Latamoxef, Imipenem, and Aztreonam revealed various antibiotic sensitivity patterns. To identify the mechanism of resistance, we examined whether the blaIMP and SHY-related genes were present in bacteria showing a high resistance to cefotaxime. The blaIMP gene was detected in 20 strains of S. marcescens, one strain of K. pneumoniae, and one strain of E. cloacae, suggesting that the blaIMP gene has widely penetrated many types of Gram-negative bacteria. The SHY-related gene was detected in one strain of S. marcescens, three strains of K. pneumoniae, and two strains of E. cloacae. We also conducted genome analyses using pulsed-field gel electrophoresis following restriction-enzyme digestion of the entire bacterial genome DNA. The SpeI-cutting patterns revealed that the 41 S. marcescens strains shared 12 identical genome patterns. This high number of shared genome patterns demonstrates the wide prevalence of resistance-gene transmis-sion between bacteria, and indicates that steps are needed to prevent cross-infection of bacteria in hospitals.