Longitudinal Study of
            <i>Escherichia coli</i>
            O157:H7 in a Beef Cattle Feedlot and Role of High-Level Shedders in Hide Contamination

Experimental oral challenge studies with three different genotypes of Escherichia coli O157:H7 were conducted in cattle to determine the genotype-specific variability in shedding frequencies and concentrations and the frequency and extent of contamination of the environment. The results indicated that the E. coli O157:H7 genotype and ecological origin maybe important factors for the occurrence and concentration in the cattle host. Four groups of six young Holstein steers each were orally challenged with 10 6 CFU of one of three E. coli O157:H7 strains: FRIK 47 (groups 1 and 2), FRIK 1641 (group 3), and FRIK 2533 (group 4). Recto-anal mucosal swabs (RAMS) and environmental samples were taken on alternate days over 30 days. The numbers of E. coli O157:H7 cells and generic E. coli cells per sample were determined. Also, the presence and absence of 28 gene targets were determined for 2,411 isolates using high-throughput real-time PCR. Over the study period, strains FRIK 47, FRIK 1641, and FRIK 2533 were detected in 52%, 42%, and 2% of RAMS, respectively. Environmental detection of the challenge strains was found mainly in samples of the hides and pen floors, with strains FRIK 47, FRIK 1641, and FRIK 2533 detected in 22%, 27%, and 0% of environmental samples, respectively. Based on the panel of 28 gene targets, genotypes of enterohemorrhagic E. coli (EHEC) and generic E. coli from the experimental samples were clustered into three subgroups. In conclusion, the results suggested that the type and intensity of measures to control this pathogen at the preharvest level may need to be strain specific.

Section: Discussioncontrasting

confidence: 49%

Differences in Colonization and Shedding Patterns after Oral Challenge of Cattle with Three Escherichia coli O157:H7 Strains

Kulow

Gonzales

Pertzborn

et al. 2012

“…Although the significance of cattle shedding high concentrations of E. coli O157:H7 is not fully understood, there is evidence that, at harvest, the prevalence of high shedders is positively associated with hide and carcass contamination (8,12). It also has been proposed that high shedders are responsible for increased transmission of E. coli O157:H7 within a cohort (1,15), possibly by increasing the concentration of the organism in the environment (25). Although the reason cattle shed high concentrations of E. coli O157:H7 is not known, we surmise that more cattle shedding higher concentrations of the organisms increase the food safety risk.…”

Section: Discussionmentioning

confidence: 99%

Inclusion of Dried or Wet Distillers' Grains at Different Levels in Diets of Feedlot Cattle Affects Fecal Shedding of Escherichia coli O157:H7

Jacob

Paddock

Renter

et al. 2010

Our objectives were to evaluate the prevalence of Escherichia coli O157:H7 in cattle fed diets supplemented with 20 or 40% dried distillers' grains (DG) (DDG) or wet DG (WDG) and assess whether removing DG from diets before slaughter affected fecal shedding of E. coli O157:H7. Eight hundred forty steers were allocated to 70 pens (12 steers/pen). Treatments were no DG (control), 20% DDG or WDG, and 40% DDG or WDG, and each was replicated in 14 pens. In phase 1, eight floor fecal samples were collected from each pen every 2 weeks for 12 weeks for isolation of E. coli O157:H7 and detection of high shedders. In phase 2, half of the pens with DG were transitioned to the no-DG control diet, and pen floor fecal samples were collected weekly from all pens for 4 weeks. During phase 1, prevalence of E. coli O157:H7 was 20.8% and 3.2% for high shedders. The form of DG had no significant effect on fecal E. coli O157:H7 shedding. The prevalence levels of E. coli O157:H7 and the numbers of high shedders were not different between diets with 0 or 20% DG; however, cattle fed 40% DG had a higher prevalence and more high shedders than cattle fed 0 or 20% DG (P < 0.05). During phase 2, overall and high-shedder prevalence estimates were 3.3% and <0.1%, respectively, and there were no differences between those for different DG forms and inclusion levels or when DG was removed from diets. The form of DG had no impact on E. coli O157:H7; however, fecal shedding was associated with the DG inclusion level.Cattle are asymptomatic reservoirs for Escherichia coli O157:H7, a food-borne pathogen associated with gastrointestinal disease in thousands of Americans each year. The organism colonizes the hindgut of cattle (18,27) and is shed in cattle feces. Once shed, E. coli O157:H7 can contaminate food and water, creating a food safety risk (20). Contamination of beef products occurs during slaughter and is associated with the prevalence of E. coli O157:H7 in feces and on the hides of cattle at harvest (5,8,12).The prevalence of E. coli O157:H7 in cattle is associated with many factors, including season, geographic location, and diet. Previous work has shown that cattle fed diets containing distillers' grains (DG), an ethanol fermentation coproduct, have a higher prevalence of E. coli O157:H7 than cattle fed diets without DG (10, 28). Distillers' grains are a valuable feed commodity for cattle producers, and use of these coproducts has increased with the expansion of the ethanol industry (14, 17). Distillers' grains for use in cattle diets are available in wet (WDG) or dry (DDG) form. The association between feeding DG and E. coli O157:H7 prevalence has been shown with both forms (10, 28), but no study has directly compared the two forms. The levels of DG supplementation in cattle diets generally range from 10 to 50% (dry matter basis) depending on whether the coproduct is used as a protein or energy source. As a protein supplement, DG is included at 10 to 15%; as an energy source, the DG level is generally dictated by coproduct availability an...

“…The mechanism underlying the seasonal variation in cattle STEC O157 colonization is an important question because the summertime increases in the prevalence may overwhelm postharvest food safety measures (28,(38)(39)(40), increasing the risk of food contamination, human infection, and disease. Furthermore, identification of the source(s) of seasonal variation in cattle colonization may lead to identification of novel control measures that might significantly reduce the public health burden associated with this pathogen.…”

Section: Discussionmentioning

confidence: 99%

Standardized Escherichia coli O157:H7 Exposure Studies in Cattle Provide Evidence that Bovine Factors Do Not Drive Increased Summertime Colonization

Sheng

Shringi

Baker

et al. 2016

The increased summertime prevalence of cattle carriage of enterohemorrhagic Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) is associated with the increased summertime incidence of human infection. The mechanism driving the seasonality of STEC O157 carriage among cattle is unknown. We conducted experimental challenge trials to distinguish whether factors extrinsic or intrinsic to cattle underlie the seasonality of STEC O157 colonization. Holstein steers (n ‫؍‬ 20) exposed to ambient environmental conditions were challenged with a standardized pool of STEC O157 strains four times at 6-month intervals. The densities and durations of rectoanal junction mucosa (RAJ) colonization with STEC O157 were compared by season (winter versus summer), dose (10 9 CFU versus 10 7 CFU), and route of challenge (oral versus rectal). Following summer challenges, the RAJ STEC O157 colonization density was significantly lower (P ‫؍‬ 0.016) and the duration was shorter (P ‫؍‬ 0.052) than for winter challenges, a seasonal pattern opposite to that observed naturally. Colonization was unaffected by the challenge route, indicating that passage through the gastrointestinal microbiome did not significantly affect the infectious dose to the RAJ. A 2-log reduction of the challenge doses in the second-year trials was accompanied by similarly reduced RAJ colonization in both seasons (P < 0.001). These results refute the hypothesis that cattle are predisposed to STEC O157 colonization during the summer months, either due to intrinsic factors or indirectly due to gastrointestinal tract microbiome effects. Instead, the data support the hypothesis that the increased summertime STEC O157 colonization results from increased seasonal oral exposure to this pathogen. Shiga toxin-producing Escherichia coli serotype O157:H7 (STEC O157) is an important zoonotic pathogen estimated to cause Ͼ70,000 cases of human infection annually in the United States (1, 2). Human disease is characterized by mild to severe, frequently hemorrhagic diarrhea, and the development of a severe sequela, the hemolytic-uremic syndrome, in approximately 5 to 10% of patients (3). Cattle are an important asymptomatic reservoir host of STEC O157, which may be transmitted to humans by ingestion of contaminated meat, produce, or water or by direct contact with cattle carrying the pathogen (4-6). The seasonal variation in STEC O157 fecal shedding by cattle, specifically the higher summertime prevalence, occurs in diverse regions, including Canada, England, Italy, South Korea, the Netherlands, Turkey, and the United States (7-20). Similar summertime peak shedding is also reported in sheep (11,15,21). Contrary patterns have been occasionally reported, including a higher wintertime prevalence (22, 23) or no seasonal variation (24-26); however, these are unusual and sometimes are confounded by other factors such as a change to indoor housing (22).The seasonal summertime shedding of STEC O157 in cattle parallels both seasonal increases in carcass contamination at abattoirs and the in...