Survival and distribution of Escherichia coli O157 in bovine manure
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Escherichia coli 0157:H7 has become one of the most important emerging foodborne pathogens with many recent outbreaks being associated with cattle. Although estimates of E. co//0157:H7 prevalence in cattle have increased over time likely due improvements in detection methodologies, fecal collection methodologies and sample transport conditions from farm to microbiological laboratories for further analysis may be factors for underestimation of prevalence of this pathogen. In this study, a new sampling methodology was analyzed and comparison of survival of E. coli 0157:H7 in feces of cattle under various experimental conditions was also determined. For the first part of the study, bovine fecal samples were inoculated with a cocktail of four different antibiotic resistant E. co//0157:H7 strains. Each inoculated sample was subdivided and subjected to each of the four following conditions: 37°C, room temperature (23''C), refrigeration temperature (4.4°C) and in plastic coolers with refrigerant packs in order to simulate transportation conditions. Samples from each of the temperature conditions were taken at 0 h, 24 h, 48 h, 120 h, and 144 h and subjected to detection and quantification of E. coli 0157:H7. Overall, holding samples at temperatures equal to or below to 23° C resulted in detectable populations for up to 168 h. At 37°C, samples were not recovered by any of the methods used after 48 hours. These results indicate that holding samples at room temperature or lower for up to 168 h prior to processing will not reduce the pathogen's population. For the second part of the study, the objective was to evaluate fecal pat sampling strategies to improve accuracy of E. co//0157:H7 prevalence estimates. A total of 120 fresh fecal pats from cattle were used in this study. From each fecal pat five samples were collected systematically going from West to East (positions 1 to 5 respectively) in north to south lines direction to avoid cross contamination and cultured for E. coli 0157:H7 within two hours using IMS separation. Of the 120 fecal pats, 96 (80%) had no positive samples in any of the 5 samples. One sample was positive in 13 of the pats, 2 in 4 of the pats, 3 in 2 of the pats, 4 in 3 of the pats and only 2 of the pats had all 5 samples positive. Of the 600 total sub-samples analyzed, 49 were positive with 14, 9, 8, 8, and 10 on position 1,2,3, 4, and 5 respectively. An increase in the prevalence of 2.45-fold (from 8.17% to 20%) was observed when sampling 5 positions per fecal pat as compared to the estimated prevalence obtained when just 1 sub-sample was obtained. Prevalence estimates may be underestimated as a result of an uneven distribution in fecal material; therefore sampling procedure plays a critical role in E. co//0157:H7 detection in bovine fecal pats.