A cross-sectional study of bacterial contamination in plant-protein feed from feed stores in Northern Virginia and Maryland

The objectives of this study were to estimate the prevalence of the enteric microbes: Escherichia coli, Salmonella, Campylobacter and Enterococcus spp., in plant-protein-based animal feed products and milk replacer and to identify risk factors associated with contamination by these bacteria. A cross-sectional survey of 158 plant-derived feed and milk replacer samples was conducted using eight animal feed stores in Northern Virginia and Maryland from January 2002 to September 2002. Overall, all samples were negative for Campylobacter; one sample (0.6%) was positive for Salmonella; nine samples (5.7%) were positive for E. coli and 80 samples (50.6%) were positive for Enterococcus. Positive samples included: whole maize, cracked peanut, cotton seed, mixed grain horse feed, and milk replacer. Samples collected during the month of January (winter) had a lower prevalence of contamination with enteric bacteria than samples collected in August and September (summer/autumn). Samples collected in January 2002 were negative for both E. coli and Salmonella. Samples collected in August and September 2002 included one Salmonella positive, and nine E. coli positive. Animal feed purchased during August and September had a 38-fold increase (95% CI: 15.60-95.16) in the risk of contamination by Enterococcus than those samples purchased during January and February of that same year (P<0.001). Enterococcus positive samples were eight times more likely to also be E. coli positive than Enterococcus negative samples (95% CI: 1.04-70.12). Non-pelleted feed was 13 times more likely to be contaminated with Enterococcus than pelleted feed (95% CI: 3.02-59.84).