Purpose: Our objective was to assess differences in persistence of Salmonella, Escherichia coli, and viral pathogens within fecal samples collected from 7 different birds and mammals.
Methods: Manure samples were obtained fresh from animals on or near the CANR Farm (Newark, DE). Samples (25g) were inoculated with 106 CFU/g or 104 CFU/g rifampicin-resistant Salmonella (6), E. coli (5), or a viral cocktail containing hepatitis A virus, murine norovirus, and Tulane virus. Samples were assessed after incubation at 20°C over 12 months. Bacterial samples were enumerated on TSA containing 80 µg/ml Rifampicin and 50 µg/ml Cycloheximide. Viral samples were frozen at 4°C, RNA extracted and viral genomes detected by qRT-PCR.
Results: Initial E. coli growth was observed in deer, waterfowl and cattle feces with highest concentrations at 15 days post-inoculation (dpi) of 7.50 log CFU/g. Following this, bacteria declined in these fecal samples and by 243 dpi concentrations of 4.93 log CFU/g cattle feces and 0.5 log CFU/g deer feces were detected. Bacteria in high and low inoculum samples were at equivalent levels within 30-45 dpi. Bacteria in waterfowl feces were found to be below the detection limit (1.5 CFU/g) in all samples at 56 dpi. Initial Salmonella growth was noted in all fecal types except for chicken, in which samples were below the detection limit and negative for both E. coli and Salmonella following sample enrichment. At 7 and 28 dpi, bacteria in raccoon and pig feces were below the detection limit, respectively. After 10 months, bacteria continue to be detectable in fecal samples from deer, sheep, and cattle. Further analysis continues on the virus samples.
Significance: As inferred from epidemiological evidence, cattle and deer feces were the most suitable for long-term persistence of E. coli and Salmonella, supporting growth and survival over ten months.