title: Perspectives on super-shedding of Escherichia coli O157:H7 by cattle.
abstract: Escherichia coli O157:H7 is a foodborne pathogen that causes illness in humans worldwide. Cattle are the primary reservoir of this bacterium, with the concentration and frequency of E. coli O157:H7 shedding varying greatly among individuals. The term "super-shedder" has been applied to cattle that shed concentrations of E. coli O157:H7 ≥ 10⁴ colony-forming units/g feces. Super-shedders have been reported to have a substantial impact on the prevalence and transmission of E. coli O157:H7 in the environment. The specific factors responsible for super-shedding are unknown, but are presumably mediated by characteristics of the bacterium, animal host, and environment. Super-shedding is sporadic and inconsistent, suggesting that biofilms of E. coli O157:H7 colonizing the intestinal epithelium in cattle are intermittently released into feces. Phenotypic and genotypic differences have been noted in E. coli O157:H7 recovered from super-shedders as compared to low-shedding cattle, including differences in phage type (PT21/28), carbon utilization, degree of clonal relatedness, tir polymorphisms, and differences in the presence of stx2a and stx2c, as well as antiterminator Q gene alleles. There is also some evidence to support that the native fecal microbiome is distinct between super-shedders and low-shedders and that low-shedders have higher levels of lytic phage within feces. Consequently, conditions within the host may determine whether E. coli O157:H7 can proliferate sufficiently for the host to obtain super-shedding status. Targeting super-shedders for mitigation of E. coli O157:H7 has been proposed as a means of reducing the incidence and spread of this pathogen to the environment. If super-shedders could be easily identified, strategies such as bacteriophage therapy, probiotics, vaccination, or dietary inclusion of plant secondary compounds could be specifically targeted at this subpopulation. Evidence that super-shedder isolates share a commonality with isolates linked to human illness makes it imperative that the etiology of this phenomenon be characterized.
authors.affiliation: 1 Agriculture and Agri-Food Canada, Lethbridge Research Centre , Lethbridge, Alberta, Canada .
authors.forename: Krysty D
authors.initials: KD
authors.lastname: Munns
authors.forename: L Brent
authors.initials: LB
authors.lastname: Selinger
authors.forename: Kim
authors.initials: K
authors.lastname: Stanford
authors.forename: Leluo
authors.initials: L
authors.lastname: Guan
authors.forename: Todd R
authors.initials: TR
authors.lastname: Callaway
authors.forename: Tim A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000818:Animals; D057138:Bacterial Shedding; D018441:Biofilms; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology* / Q000517:prevention & control / Q000635:transmission; D004197:Disease Reservoirs; D004927:Escherichia coli Infections / Q000382:microbiology / Q000517:prevention & control / Q000635:transmission / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000502:physiology; D005243:Feces / Q000382:microbiology; D005517:Foodborne Diseases / Q000209:etiology / Q000382:microbiology / Q000517:prevention & control; D005759:Gastroenteritis / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary*; D041981:Gastrointestinal Tract / Q000382:microbiology; D006801:Humans; D008460:Meat / Q000382:microbiology; D050296:Microbial Viability; D008954:Models, Biological; D015047:Zoonoses / Q000209:etiology / Q000382:microbiology / Q000517:prevention & control