Genetic diversity of community and hospital- acquired Klebsiella pneumoniae strains producing CTX-M extended-spectrum β -lactamases in Croatia

This study was conducted to detect and analyze the presence of extended-spectrum β -lactamase (ESBL)-producing Klebsiella pneumoniae within clinical isolates of both community- and hospital-based patients in Croatia and to characterize bla CTX-M genes and their environment in these isolates. Six hundred forty eight consecutive non-duplicate K. pneumoniae isolates were collected from October 2006 to January 2007. One hundred and twenty eight K. pneumoniae isolates were selected for further study on the basis of positive double disc diffusion test for ESBL production. Minimal inhibitory concentrations (MICs) were determinated by broth microdilution method according to CLSI. The transferability of cefotaxime resistance was tested by conjugation (broth mating method). PCR was used to detect alleles encoding CTX-M enzymes. The genotypes of the strains were compared by analysis of banding patterns generated by pulsed-field gel electrophoresis (PFGE) of Xba I-digested genomic DNA. Thirty-three strains were found to possess CTX-M β -lactamases. Fifty six percent of the CTX-M producing strains originated from hospital and 44% were obtained from the community patients. PFGE demonstrated three major similarity clusters according to Tenover criteria. All CTX-M positive K.pneumoniae strains belonged to group 1 of CTX-M β - lactamases. Sequencing of the PCR products of representative strains belonging to major clusters revealed presence of CTX-M-15 β - lactamases.