Abstract

Background: Resistance to beta-Lactam antibiotics in Enterobacteriaceae is increasing worldwide; however, information about the different beta-Lactamase genes in diverse regions is scarce. We aimed to identify beta-lactamse genes in presumably ESBL positive isolates of Enterobacteriaceae.
Methods: A nonredundant collection of 757 strains of E. coli, Klebsiella pneumonia, Klebsiella oxytoca and Enterobacter cloacae resistant to third generation cephalosporins and ESBL positive by VITEK II analysis was analyzed by PCR for presence of beta-lactamase genes of the TEM, SHV, CTX-M and ampC families.
Results: Distribution of patient age was bimodal, with peaks at <1 year of age and at 60-80 years age. the mean number beta-lactamase genes detected per strain was 2.01 (range 0-6), with E. cloacae tending to have more beta-lactamase genes than E. coli or Klebsiella spp. CTX-M genes, in particular from subgroup I, were most frequently detected, followed by SHV and TEM genes. Only 10% of the strains examined were positive for ampC genes. E. coli and K. pneumonia harbored ampC genes from several subgroups, while in E. cloacae and K. oxytoca, only EBC ampC genes were detected. Regarding overall beta-Lactamase diversity, E. coli and K. pneumonia have fewer, more dominating strains than K. oxytoca and E. cloacae, where the contribution of the most frequent strains to overall diversity is much lower. In 47 strains from 23 patients, we found evidence of horizontal plasmid transfer occurring in vivo. Thus, among patients harboring >1 ESBL positive bacterial species, 71% may have been repeatedly colonized by different strains, while in 29%, plasmid transfer may have occurred after a single colonization event.
Conclusions: The molecular epidemiology of beta-Lactamase genes is complex even if analyzed in a single institution. CTX-M enzymes dominate, and co-occurrence of ampC enzymes is rare. Plasmid transfer between species of Enterobacteriaceae seems to occur in vivo in some patients.