MOLECULAR EPIDEMIOLOGY OF KLEBSIELLA-PNEUMONIAE PRODUCING SHV-5 BETA-LACTAMASE - PARALLEL OUTBREAKS DUE TO MULTIPLE PLASMID TRANSFER

Over a period of 22 months, 32 patients treated in three independent i ntensive care units of the Innsbruck University Hospital were infected with extended-spectrum beta-lactamase-producing members of the family Enterobacteriaceae (30 Klebsiella pneumoniae isolates, 1 Klebsiella o xytoca isolate, and 1 Escherichia coli isolate), As confirmed by seque ncing of a bla gene PCR fragment, all isolates expressed the SHV-5-typ e beta-lactamase. Genomic fingerprinting of epidemic strains with XbaI and pulsed-field gel electrophoresis grouped 20 of 21 isolates from w ard A into two consecutive clusters which included 1 of 3 ward B isola tes. All six K. pneumoniae isolates from ward C formed a third cluster . Stool isolates of asymptomatic patients and environmental isolates b elonged to these clusters as well. Additionally, 2,600 routine K. pneu moniae isolates from the surrounding provinces (population, 900,000) w ere screened for SHV-5 production. Only one of six nonepidemic isolate s producing SHV-5 beta-lactamase was matched with the outbreak strains by genomic fingerprinting. Plasmid fingerprinting, however, revealed the epidemic spread of a predominant R-plasmid, with a size of approxi mately 80 kb, associated with 29 of the 30 K. pneumoniae isolates. Thi s plasmid was also present in the single K. oxytoca and E. coli isolat es from ward C and in three nonepidemic isolates producing SHV-5. Our results underline that strain typing exclusively on the genomic level can be misleading in the epidemiological investigation of plasmid-enco ded extended-spectrum beta-lactamases. Our evidence for multiple event s of R-plasmid transfer between species of the family Enterobacteriace ae in this nosocomial outbreak stresses the need for plasmid typing, e specially because SHV-5 beta-lactamase seems to be regionally spread p redominantly via plasmid transfer.