Bacteriophage isolated from feedlot cattle can reduce Escherichia coli O157:H7 populations in ruminant gastrointestinal tracts.

Escherichia coli O157:H7 can live undetected in the gut of food animals and be spread to humans directly and indirectly. Bacteriophages are viruses that prey on bacteria, offering a natural, nonantibiotic method to reduce pathogens from the food supply. Here we show that a cocktail of phages isolated from commercial cattle feces reduced E. coli O157:H7 populations in the gut of experimentally inoculated sheep. A cocktail of phages was used in order to prevent the development of resistance to the phages. In our first in vivo study we found that our cocktail of phages reduced E. coli O157:H7 populations in the feces of sheep (p < 0.05) by 24 hours after phage treatment. Upon necropsy, populations of inoculated E. coli O157:H7 were reduced by phage treatment in both the cecum (p < 0.05) and rectum (p < 0.1). In our second in vivo study, several ratios of phage plaque-forming units (PFU) to E. coli O157:H7 colony-forming units (CFU) were used (0:1, 1:1, 10:1, and 100:1 PFU/CFU) to determine the most efficacious phage dose. A 1:1 ratio of phage to bacteria was found to be more effective (p < 0.05) than either of the higher ratios used (10:1 or 100:1). Ruminal levels of E. coli O157:H7 were not significantly reduced (p > 0.10) in any of the studies due to relatively low inoculated E. coli O157:H7 ruminal populations. Our results demonstrate that phage can be used as a preharvest intervention as part of an integrated pathogen reduction scheme.

Seasonal shedding of Escherichia coli O157:H7 in ruminants: a new hypothesis.

Seasonal shedding of Escherichia coli O157:H7 in ruminants is well documented; however, viable explanations for this phenomenon are lacking. The fecal prevalence of E. coli O157:H7 in ruminants is the highest in the summer months, decreasing to low or undetectable levels in the winter. To determine if day length is correlated to seasonal shedding, nine reports of E. coli O157:H7 prevalence in cattle were selected for similarity of sampling technique, culture methodology, cattle type, and ability to determine approximate sampling month and location, representing three regions in North America (southern Canada, midwestern United States, and the southern United States/Mexico). Correlation and regression analysis revealed a positive correlation existed between day length (r = 0.67; R2 = 0.45; P = 0.0009) and, to a lesser extent, ambient temperature (r = 0.43; R2 = 0.19; P = 0.05) and E. coli O157:H7 prevalence. Based on these results, a study was conducted in a commercial feedlot to examine the effect of artificial lighting on E. coli O157 prevalence. Four pens of cattle received approximately 5 hours of artificial lighting daily (in addition to the natural light) for 60 days and four pens served as controls. Freshly voided fecal samples (representing approximately 30% of the steers/pen) were collected from the pen floor and cultured for E. coli O157 after 25 and 53 days of artificial lighting and 28 and 43 days following cessation of the lighting treatment. Fecal prevalence of E. coli O157 remained constant in the lighted pens whereas prevalence was lower (P < 0.01) in the control treatment after 53 days of lighting. Forty-three days following cessation of the lighting treatment, prevalence decreased in the lighted treatment group to levels comparable (P > 0.20) to control levels. Understanding the mechanisms underlying the seasonality of this important foodborne pathogen will enable the implementation of effective control strategies when it is most prevalent.

Salmonella genotype diversity in nonlactating and lactating dairy cows.

Dairy cows may serve as asymptomatic carriers of Salmonella. The potential for herd carrier status increases with herd size, and Salmonella shedding may be triggered by stresses placed on the animals. The scope of the current study is to determine the effects lactation may have on Salmonella genotypic diversity among detected serotypes. Fecal samples were collected on two sampling dates from 60 nonlactating and 60 lactating Holstein cows. No serotype was predominant over the two collection dates, although Salmonella Albany, Salmonella Anatum, Salmonella Newport, and Salmonella Senftenberg were detected in relatively high numbers. Twenty-three genotypes were detected on the first date and 27 on the second date. The greatest genotypic diversity was seen among Salmonella Newport and Salmonella Senftenberg, with five and nine genotypes, respectively. The presence of multiple serotypes and genotypes in the herd suggests multiple contamination sources. However, there was no conclusive effect of lactation status of the cows on Salmonella genotypic shedding.