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.

A comprehensive TnphoA mutant library was constructed in Yersinia pestis KIM6 to identify surface proteins involved in Y. pestis host cell invasion and bacterial virulence. Insertion site analysis of the library repeatedly identified a 9,042-bp chromosomal gene (YPO3944), intimin/invasin-like protein (Ilp), similar to the Gram-negative intimin/invasin family of surface proteins. Deletion mutants of ilp were generated in Y. pestis strains KIM5(pCD1 ؉ ) Pgm ؊ (pigmentation negative)/, KIM6(pCD1 ؊ ) Pgm ؉ , and CO92. Comparative analyses were done with the deletions and the parental wild type for bacterial adhesion to and internalization by HEp-2 cells in vitro, infectivity and maintenance in the flea vector, and lethality in murine models of systemic and pneumonic plague. Deletion of ilp had no effect on bacterial blockage of flea blood feeding or colonization. The Y. pestis KIM5 ⌬ilp strain had reduced adhesion to and internalization by HEp-2 cells compared to the parental wild-type strain (P < 0.05). T he genus Yersinia is comprised of 12 species, three of which, Yersinia enterocolitica, Yersinia pseudotuberculosis, and Yersinia pestis, are pathogenic for humans and rodents (5). Y. pestis, the causative agent of plague, is typically transmitted subcutaneously to humans by the bite of an infected flea, causing either bubonic or septicemic plague, but can also be transmitted by aerosols, causing pneumonic plague (25). Pathogenesis of Y. pestis is dependent on the presence of three plasmids: pCD1 encoding a type III secretion system, pPCP1 encoding plasminogen activator (Pla), and pMT1 encoding the capsular antigen fraction 1 (Caf1) (25). Y. pestis has been considered an extracellular pathogen because it contains mutations in two major invasin and adhesin homologues (Inv and YadA) found in invasive Y. pseudotuberculosis (24, 29). However, recent studies demonstrate that Y. pestis is able to invade eukaryotic cells mediated in part by Pla, capsular F1 antigen, OmpX (Ail), and Psa fimbriae (3,18,20,21). None of these factors alone confers the full invasion phenotype.To identify additional Y. pestis surface proteins that may contribute to invasion and virulence, a comprehensive TnphoA insertion library of avirulent Y. pestis KIM6(pCD1 Ϫ ) Pgm ϩ (pigmentation positive) was generated. This avirulent strain was used because it lacks the well-characterized type III secretion system and effector Yop genes on pCD1, and therefore the phoA fusions would be biased toward uncharacterized chromosomal loci. The DNA sequence of transposon insertion junctions was determined, and insertionally inactivated gene DNA sequences were compared to bacterial DNA sequence databases. In this screen, DNA sequence analysis repeatedly identified insertions in a large gene of 9,042 bp (YPO3944) which we designated ilp (intimin/invasinlike protein), with predicted similarity to the class of Gram-negative bacterial intimin/invasin/autotransporter proteins. Because computer analysis of Ilp predicted a three-dimensional structure similar to the C-typ...

The objectives of this study were to investigate the microbial contamination level of domestic kitchen environments and to provide information to improve food safety in 50 domestic house kitchens located in Seoul, Incheon, and Gyeonggi-do. Dishcloth, chopping board, and refrigerator swabs were examined for the presence of coliforms, Salmonella spp., Campylobacter jejuni/coli, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus. The means and standard deviations of coliform counts for dishcloths was 4.8 ± 1.84 log CFU/100 g, chopping boards, and refrigerator drawers were 4.04 ± 1.53, 4.11 ± 1.65 log CFU/100 cm 2 , respectively. Salmonella spp. and Campylobacter jejuni/coli were not detected in all samples. E. coli were detected in 3 on the dishcloths and 1 of 50 samples in the refrigerator drawer. Listeria monocytogenes was detected in the drawer of the refrigerator in 2 of 50 samples. In the case of Staphylococcus aureus, the detection on dishcloths, chopping boards, and drawers in refrigerators was 21, 12, and 14 of 50 samples, respectively. The results of microbiological tests of domestic kitchen utensils can be used to emphasize the importance of the sanitary conditions in domestic kitchen environments.