Identification of a mutation in the pst-phoU operon that reduces pathogenicity of an Escherichia coli strain causing septicemia in pigs.

We used transposon (TnphoA) mutagenesis to study the role of virulence factors of pathogenic Escherichia coli strains associated with septicemia in calves and piglets. We have produced an avirulent and serum-sensitive mutant of wild-type pathogenic strain 5131 O115:K"V165":F165 and have localized and identified the TnphoA insertion in the pstC gene of the pst-phoU operon. This operon encodes the PstSCAB transporter and PhoU protein that negatively regulate the phosphate (Pho) regulon. This mutation is pleiotropic and could have an effect on pathogenicity and on the production of the surface polysaccharides of strain 5131. The mutant demonstrated restored repressibility of alkaline phosphatase and regained the capacity to resist serum and to survive systemically for at least 5 days in experimentally inoculated pigs when complemented with plasmid pAN92, bearing the pst-phoU operon.