Evaluation of commercially manufactured animal feeds to determine presence of Salmonella, Escherichia coli, and Clostridium perfringens

Summary: The following research report provides information regarding the bacterial contamination that exists in feed ingredients and mixed animal feeds collected from 4 commercial feed mills and the research feed mill from Auburn University. The experiment was conducted to establish if feed ingredients or commercial animal feeds serve as sources of contamination of Salmonella, Escherichia coli (EC), and Clostridium perfringens. During microbiological isolation, an unknown group of bacteria belonging to the Clostridium genus was identified. Therefore, the second aim of this research was to characterize the unknown group of bacteria. No Salmonella serovars were detected on ingredients or feed samples collected; however, the presence of C. perfringens was confirmed in some mixed animal feeds. Peanut meal and corn gluten meal were the ingredients with highest contamination of Clostridium spp. (CS), and peanut meal and corn meal for EC. Soybean meal and distillers dried grains with solubles had the lowest contamination with CS and EC. The stage of feed processing (postmixing, postpelleting, postcooling, and loadout) did not influence the degree of contamination with CS. However, contamination with EC was higher at the postmixing stage, but it was significantly reduced after the pelleting process (9/10 times), which suggests low stability of EC during thermal processing. Recontamination of mixed feed with EC after the pelleting process was observed in 2 of 5 feed mills studied; therefore, strategies must be developed by feed mills to prevent feed recontamination after thermal processing and thus guarantee EC–free animal feed. The unknown bacteria found in mixed feeds were identified as Bacillus proteolyticus or Clostridium argentinense, the latter representing a potential risk for farm animals because of its ability to produce a neuroparalytic toxin that can cause botulism. The present research report underscores the importance of evaluating alternatives to control bacterial pathogens such as EC, C. perfringens, and C. argentinense that may be present on animal feeds.