title: Molecular subtyping and genetic analysis of the enterohemolysin gene (ehxA) from Shiga toxin-producing escherichia coli and atypical enteropathogenic E. coli.
abstract: Analyses of the distribution of virulence factors among different Escherichia coli pathotypes, including Shiga toxin-producing E. coli (STEC), may provide some insight into the mechanisms by which different E. coli strains cause disease and the evolution of distinct E. coli types. The aim of this study was to examine the DNA sequence of the gene for enterohemolysin, a plasmid-encoded toxin that readily causes the hemolysis of washed sheep erythrocytes, and to assess the distribution of enterohemolysin subtypes among E. coli isolates from various human and animal sources. The 2,997-bp ehxA gene was amplified from 227 (63.8%) of 356 stx- and/or eae-positive E. coli strains isolated from cattle and sheep and from 24 (96.0%) of 25 STEC strains isolated from humans with diarrheal disease. By using PCR and restriction fragment length polymorphism (RFLP) analysis of ehxA, six distinct PCR-RFLP types (A to F) were observed, with strains of subtypes A and C constituting 91.6% of all the ehxA-positive strains. Subtype A was associated mainly with ovine strains with stx only (P < 0.001), and subtype C was associated with bovine eae-positive strains (P < 0.001). Eleven ehxA alleles were fully sequenced, and the phylogenetic analysis indicated the presence of three closely related (>95.0%) ehxA sequence groups, one including eae-positive strains (subtypes B, C, E, and F) and the other two including mainly eae-negative STEC strains (subtypes A and D). In addition to being widespread among STEC strains, stx-negative, eae-positive strains (atypical enteropathogenic E. coli strains) isolated from cattle and sheep have similar ehxA subtypes and hemolytic activities.
authors.affiliation: Food, Metabolism and Microbiology Section, Food and Health Group, AgResearch, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand. adrian.cookson@agresearch.co.nz
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Cookson
authors.forename: Jenny
authors.initials: J
authors.lastname: Bennett
authors.forename: Fiona
authors.initials: F
authors.lastname: Thomson-Carter
authors.forename: Graeme T
authors.initials: GT
authors.lastname: Attwood
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D054308:Enteropathogenic Escherichia coli / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D006461:Hemolysis; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D017422:Sequence Analysis, DNA; D012756:Sheep; D022622:Shiga Toxin 1 / Q000235:genetics / Q000378:metabolism; D022641:Shiga Toxin 2 / Q000235:genetics / Q000378:metabolism; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity
chemical_list: D018829:Adhesins, Bacterial; D001427:Bacterial Toxins; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; C036507:Hlya protein, E coli; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2; C073819:eaeA protein, E coli