Detection and molecular genetics of extended-spectrum beta-lactamases among cefuroxime-resistant Escherichia coli and Klebsiella spp. isolates from Finland, 2002-2004.

Extended-spectrum beta-lactamase (ESBL) producing Escherichia coli and Klebsiella spp. isolates are spreading and becoming an increasing problem concerning treatment, diagnostics and hospital hygiene. We wanted to discover which genotypes are occurring in Finland and to assess the CLSI screening method. The isolates were collected from 26 laboratories during a 3-y period from 2002 to 2004. We studied the zone diameters by disk diffusion according to CLSI recommendations. ESBL genes were detected by PCR and the TEM and SHV genes were sequenced traditionally, while the CTX-M isolates were analysed with pyrosequencing. Of the 402 isolates included in the study, 269 (67%) were confirmed to be ESBL producers according to the CLSI criteria. The CTX-M genes were the most prevalent, especially the combination of a CTX-M-1-group and a TEM-1 gene. In our material there were few isolates that had an ESBL gene but were negative in the CLSI ESBL confirmatory test. During recent y especially the CTX-M producing isolates have increased in Europe and now they are also found in Finland with increasing prevalence.