title: Genetic characterization of a diverse Escherichia coli O157:H7 population from a variety of farm environments.
abstract: Many of the current studies on the genetic diversity of Escherichia coli O157:H7 have focused on pathogenic clinical, veterinary, or food isolates. These studies did not explore the diversity of the larger population in the farm environment. Research on selected farm isolates address this wider diversity but have typically been limited to a specific geographic locale or farm type, thus giving limited insight into the greater diversity across geographic regions and varied environments. The objective of this study was to evaluate a diverse population of E. coli O157:H7 collected from a variety of locations and farm environments. Eighty-eight isolates were collected from four farm types (swine, dairy, beef, and poultry) across the southeastern and western United States. Eighteen farms were sampled every 3 months over a period of 24 months. Isolates were analyzed by ribotyping and pulsed field gel electrophoresis (PFGE). Real-time PCR was used to determine the presence or absence of key pathogenic genes (stx1, stx2, and eae). The data indicate a significant amount of genetic diversity, however, ribotype analysis revealed meaningful clusters within the larger population. These groupings were consistent with PFGE analysis. Most of these isolates were clustered by location (i.e. from the same state or region) or farm type. Of the isolates in these clusters, most did not contain pathogenic genes. Of notable interest is a single group in which the majority of isolates, collected from four of the five states sampled, contained at least one stx gene and the eae gene suggesting the existence of a specific pathogenic cluster. These data suggest that, while there is notable diversity within the broader E. coli O157:H7 population, pathogenic isolates may be limited to a subset of strains within the population.
authors.affiliation: Food Science and Technology Department, The University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Richards
authors.forename: D
authors.initials: D
authors.lastname: Pérez-Conesa
authors.forename: C A
authors.initials: CA
authors.lastname: Doane
authors.forename: B E
authors.initials: BE
authors.lastname: Gillespie
authors.forename: J R
authors.initials: JR
authors.lastname: Mount
authors.forename: S P
authors.initials: SP
authors.lastname: Oliver
authors.forename: P
authors.initials: P
authors.lastname: Pangloli
authors.forename: F A
authors.initials: FA
authors.lastname: Draughon
mesh_terms: D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D016000:Cluster Analysis; D016521:Electrophoresis, Gel, Pulsed-Field; D004783:Environmental Microbiology; D019453:Escherichia coli O157 / Q000145:classification* / Q000235:genetics* / Q000472:pathogenicity; D014644:Genetic Variation; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D021521:Ribotyping; D022603:Shiga Toxins / Q000096:biosynthesis; D015144:Southeastern United States; D015206:Southwestern United States; D037521:Virulence Factors / Q000032:analysis*
chemical_list: D022603:Shiga Toxins; D037521:Virulence Factors