Instability of Pathogenicity Islands in Uropathogenic Escherichia coli 536

Abstract

ABSTRACT The uropathogenic Escherichia coli strain 536 carries at least five genetic elements on its chromosome that meet all criteria characteristic of pathogenicity islands (PAIs). One main feature of these distinct DNA regions is their instability. We applied the so-called island-probing approach and individually labeled all five PAIs of E. coli 536 with the counterselectable marker sacB to evaluate the frequency of PAI-negative colonies under the influence of different environmental conditions. Furthermore, we investigated the boundaries of these PAIs. According to our experiments, PAI II 536 and PAI III 536 were the most unstable islands followed by PAI I 536 and PAI V 536 , whereas PAI IV 536 was stable. In addition, we found that deletion of PAI II 536 and PAI III 536 was induced by several environmental stimuli. Whereas excision of PAI I 536 , PAI II 536 , and PAI V 536 was based on site-specific recombination between short direct repeat sequences at their boundaries, PAI III 536 was deleted either by site-specific recombination or by homologous recombination between two IS 100 -specific sequences. In all cases, deletion is thought to lead to the formation of nonreplicative circular intermediates. Such extrachromosomal derivatives of PAI II 536 and PAI III 536 were detected by a specific PCR assay. Our data indicate that the genome content of uropathogenic E. coli can be modulated by deletion of PAIs.