title: Virulence characterization and molecular subtyping of typical and atypical Escherichia coli O157:H7 and O157:H(-) isolated from fecal samples and beef carcasses in Mexico.
abstract: The objective of the study was to characterize virulence genes and subtype Escherichia coli O157:H7 and O157:H( 2 ) isolates obtained from a vertically integrated feedlot slaughter plant in Mexico. A total of 1,695 samples were collected from feedlots, holding pens, colon contents, hides, and carcasses. E. coli O157:H7 detection and confirmation was carried out using conventional microbiology techniques, immunomagnetic separation, latex agglutination, and the BAX system. A total of 97 E. coli O157 strains were recovered and screened for key virulence and metabolic genes using multiplex and conventional PCR. Eighty-eight (91.72%) of the strains carried stx2, eae, and ehxA genes. Ten isolates (8.25%) were atypical sorbitol-fermenting strains, and nine were negative for the flicH7 gene and lacked eae, stx1, stx2, and ehxA. One sorbitol-positive strain carried stx2, eae, tir, toxB, and iha genes but was negative for stx1 and ehxA. Pulsed-field gel electrophoresis (PFGE) analysis yielded 49 different PFGE subtypes, showing a high genetic diversity; however, the majority of the typical isolates were closely related (80 to 90% cutoff). Atypical O157 isolates were not closely related within them or to typical E. coli O157:H7 isolates. Identical PFGE subtypes were found in samples obtained from colon contents, feedlots, holding pens, and carcasses. Isolation of a sorbitolfermenting E. coli O157 positive for a number of virulence genes is a novel finding in Mexico. These data showed that genetically similar strains of E. coli O157:H7 can be found at various stages of beef production and highlights the importance of preventing cross-contamination at the pre- and postharvest stages of processing.
authors.affiliation: Department of Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
authors.forename: Claudia
authors.initials: C
authors.lastname: Narváez-Bravo
authors.affiliation: Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Echeverry
authors.affiliation: Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: Markus F
authors.initials: MF
authors.lastname: Miller
authors.affiliation: Department of Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
authors.forename: Argenis
authors.initials: A
authors.lastname: Rodas-González
authors.affiliation: Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: M Todd
authors.initials: MT
authors.lastname: Brashears
authors.affiliation: Agriculture and Agri-Food Canada, 6000 C&E Trail, Lacombe, Alberta, Canada T4L 1W1.
authors.forename: Mueen
authors.initials: M
authors.lastname: Aslam
authors.affiliation: Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas 79409, USA. mindy.brashears@ttu.edu.
authors.forename: Mindy M
authors.initials: MM
authors.lastname: Brashears
mesh_terms: D000818:Animals; D015373:Bacterial Typing Techniques; D002417:Cattle; D016521:Electrophoresis, Gel, Pulsed-Field; D019453:Escherichia coli O157 / Q000145:classification / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D018189:Immunomagnetic Separation; D008460:Meat / Q000382:microbiology*; D008800:Mexico; D016133:Polymerase Chain Reaction; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors