title: Population structure of rumen Escherichia coli associated with subacute ruminal acidosis (SARA) in dairy cattle.
abstract: Previous studies indicated that only subacute ruminal acidosis (SARA), induced by feeding a high-grain diet, is associated with an inflammatory response and increased abundance of Escherichia coli in the rumen. We hypothesized that ruminal E. coli in grain pellet-induced SARA carried virulence factors that potentially contribute to the immune activation during SARA. One hundred twenty-nine E. coli isolates were cultured from the rumens of 8 cows (4 animals per treatment) in which SARA had been nutritionally induced by feeding a high-grain diet (GPI-SARA) or a diet containing alfalfa pellets (API-SARA). The population structure of the E. coli was evaluated with the ABD genotyping system and repetitive sequence-based (rep)-PCR fingerprinting. Twenty-five virulence factors were evaluated with PCR. Escherichia coli numbers were higher in the GPI-SARA treatment than in the API-SARA treatment. The genetic structure of the E. coli was significantly different between SARA challenge models. Isolates from GPI-control (46%), API-control (70%), and API-SARA (53%) were closely related and fell into one cluster, whereas isolates from GPI-SARA (54%) grouped separately. The ABD typing indicated a shift from an A-type E. coli population to a B1-type population only due to GPI-SARA. Of the 25 virulence factors tested, curli fiber genes were highly associated with GPI. Curli fibers were first identified in E. coli mastitis isolates and are potent virulence factors that induce a range of immune responses. Results suggest that under low rumen pH conditions induced by a grain diet, there is a burst in the number of E. coli with virulence genes that can take advantage of these rumen conditions to trigger an inflammatory response.
authors.affiliation: Department of Animal Science, University of Manitoba, Winnipeg, MB, R3T 2N2 Canada.
authors.forename: E
authors.initials: E
authors.lastname: Khafipour
authors.forename: J C
authors.initials: JC
authors.lastname: Plaizier
authors.forename: P C
authors.initials: PC
authors.lastname: Aikman
authors.forename: D O
authors.initials: DO
authors.lastname: Krause
mesh_terms: D000138:Acidosis / Q000382:microbiology / Q000662:veterinary*; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D004032:Diet / Q000662:veterinary*; D002523:Edible Grain / Q000009:adverse effects; D004926:Escherichia coli / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D005798:Genes, Bacterial; D005838:Genotype; D006863:Hydrogen-Ion Concentration; D000455:Medicago sativa; D012417:Rumen / Q000737:chemistry / Q000382:microbiology*; D014774:Virulence; D037521:Virulence Factors / Q000032:analysis*
chemical_list: D037521:Virulence Factors