Emergence and prevalence of β-lactamase-producing Klebsiella pneumoniae resistant to cephems in Japan

Forty-six cephem-resistant Klebsiella pneumoniae strains with minimum inhibitory concentrations >8 μg/mL for cefpodoxime and cefmetazole were selected from clinical isolates obtained between 2000 and 2002 from eight hospitals on Northern Kyushu Island, Japan. We investigated the mechanisms of resistance to cephems in these 46 K. pneumoniae isolates. The results of isoelectric focusing of β-lactamases produced by these isolates, polymerase chain reaction for detection of various Class A, Class B and Class C β-lactamases, and determination of the sequence of the β-lactamase structural gene showed that most of these isolates had various types of broad-spectrum β-lactamases. Of the 46 isolates, 2 were CMY-2 β-lactamase producers and 41 were DHA-1 β-lactamase producers. Forty of the 41 DHA-1 β-lactamase producers simultaneously produced SHV-12 extended-spectrum β-lactamase (ESBL), and the remaining isolate simultaneously produced SHV-27. Furthermore, one DHA-1 and SHV-12 β-lactamase producer also produced IMP-1 β-lactamase. The only broad-spectrum β-lactamase with another isolate was IMP-1. Chromosomal DNA restriction fragment analysis using XbaI suggested that nosocomial infection due to DHA-1 and SHV-12 β-lactamase producers had occurred at two centres. This is the first report of nosocomial infection due to DHA-1 β-lactamase-producing K. pneumoniae including other plasmid-encoded AmpC β-lactamases in Japan. The mechanisms of resistance of 44 of the 46 isolates to cephalosporins and cephamycins were ESBL production and/or plasmid-encoded AmpC β-lactamase and/or IMP-1 β-lactamase production. For two isolates, the mechanism of resistance to could not be identified. These results show that it is necessary to minimise the prevalence of these resistant strains as it will be a very serious problem if organisms producing these broad-spectrum β-lactamases increase in clinical situations. It is important to detect these strains sooner and to perform rigorous infection control earlier.