Effects of single and multiple pathogenicity island deletions on uropathogenic Escherichia coli strain 536 intrinsic extra-intestinal virulence.

Background: Escherichia coli strain 536 is a uropathogenic strain harboring 7 pathogenicity islands (PAIs). Whether or not these PAIs additively contribute to extra-intestinal virulence is unknown. Methods: We tested 7 single and several multiple-PAI deletion mutants in a mouse septicemia model by monitoring mouse survival. Results: E. coli 536 mutants in which PAIs II or III were deleted showed a significant decrease in virulence compared to the wild type (WT). All other single-PAI deletion mutants were as lethal to mice as was the WT. The mutant in which all seven PAIs were deleted showed milder virulence than the mutants in which PAI III or PAIs III and IV were deleted. The mutant in which PAIs II, III, IV, V, and VII were deleted tended to be less virulent than the mutant with deletion of PAI III only. All together, these results indicate a rough additive effect of PAIs in extra-intestinal virulence. Conclusion: All PAIs of E. coli 536 do not play the same role in extra-intestinal virulence estimated in a mouse septicemia model and PAIs cooperate in an additive manner to achieve extra-intestinal virulence.