title: Phenotypic diversity of Escherichia coli O157:H7 strains associated with the plasmid O157.
abstract: Escherichia coli O157:H7, a food-borne pathogen, causes hemorrhagic colitis and the hemolytic-uremic syndrome. A putative virulence factor of E. coli O157:H7 is a 60-MDa plasmid (pO157) found in 99% of all clinical isolates and many bovine-derived strains. The well characterized E. coli O157:H7 Sakai strain (Sakai) and its pO157-cured derivative (Sakai-Cu) were compared for phenotypic differences. Sakai-Cu had enhanced survival in synthetic gastric fluid, did not colonize cattle as well as wild-type Sakai, and had unchanged growth rates and tolerance to salt and heat. These results are consistent with our previous findings with another E. coli O157:H7 disease outbreak isolate ATCC 43894 and its pO157-cured (43894-Cu). However, despite the essentially sequence identical pO157 in these strains, Sakai-Cu had changes in antibiotic susceptibility and motility that did not occur in the 43894-Cu strain. This unexpected result was systematically analyzed using phenotypic microarrays testing 1,920 conditions with Sakai, 43894, and the plasmid-cured mutants. The influence of the pO157 differed between strains on a wide number of growth/survival conditions. Relative expression of genes related to acid resistance (gadA, gadX, and rpoS) and flagella production (fliC and flhD) were tested using quantitative real-time PCR and gadA and rpoS expression differed between Sakai-Cu and 43894-Cu. The strain-specific differences in phenotype that resulted from the loss of essentially DNA-sequence identical pO157 were likely due to the chromosomal genetic diversity between strains. The O157:H7 serotype diversity was further highlighted by phenotypic microarray comparisons of the two outbreak strains with a genotype 6 bovine E. coli O157:H7 isolate, rarely associated with human disease.
authors.affiliation: Department of Microbiology, Molecular Biology, and Biochemistry, University of Idaho, Moscow, Idaho 83844, USA.
authors.forename: Ji Youn
authors.initials: JY
authors.lastname: Lim
authors.forename: Joon Bae
authors.initials: JB
authors.lastname: Hong
authors.forename: Haiqing
authors.initials: H
authors.lastname: Sheng
authors.forename: Smriti
authors.initials: S
authors.lastname: Shringi
authors.forename: Rajinder
authors.initials: R
authors.lastname: Kaul
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Besser
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Hovde
mesh_terms: D000818:Animals; D002417:Cattle; D024881:Drug Resistance, Bacterial / Q000235:genetics; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D005516:Food Microbiology; D005798:Genes, Bacterial; D014644:Genetic Variation; D006801:Humans; D010641:Phenotype; D010957:Plasmids / Q000235:genetics*; D013045:Species Specificity; D014774:Virulence / Q000235:genetics