Genetic Structure and Distribution of Four Pathogenicity Islands (PAI I 536 to PAI IV 536 ) of Uropathogenic Escherichia coli Strain 536

Abstract

For the uropathogenic Escherichia coli strain 536 (O6:K15:H31), the DNA sequences of three pathogenicity islands (PAIs) (PAI I₅₃₆ to PAI III₅₃₆) and their flanking regions (about 270 kb) were determined to further characterize the virulence potential of this strain. PAI I₅₃₆ to PAI III₅₃₆ exhibit features typical of PAIs, such as (i) association with tRNA-encoding genes; (ii) G+C content differing from that of the host genome; (iii) flanking repeat structures; (iv) a mosaic-like structure comprising a multitude of functional, truncated, and nonfunctional putative open reading frames (ORFs) with known or unknown functions; and (v) the presence of many fragments of mobile genetic elements. PAI I₅₃₆ to PAI III₅₃₆ range between 68 and 102 kb in size. Although these islands contain several ORFs and known virulence determinants described for PAIs of other extraintestinal pathogenic E. coli (ExPEC) isolates, they also consist of as-yet-unidentified ORFs encoding putative virulence factors. The genetic structure of PAI IV₅₃₆, which represents the core element of the so-called high-pathogenicity island encoding a siderophore system initially identified in pathogenic yersiniae, was further characterized by sample sequencing. For the first time, multiple PAI sequences (PAI I₅₃₆ to PAI IV₅₃₆) in uropathogenic E. coli were studied and their presence in several wild-type E. coli isolates was extensively investigated. The results obtained suggest that these PAIs or at least large fragments thereof are detectable in other pathogenic E. coli isolates. These results support our view that the acquisition of large DNA regions, such as PAIs, by horizontal gene transfer is an important factor for the evolution of bacterial pathogens.