Low Incidence of Aeromonas sp. in Livestock Feces

Pig, beef, sheep and turkey fecal specimens were assayed for recovery of inoculated Aeromonas sp. by directly plating the samples on five different agar media. Of these, starch-ampicillin was optimal with respect to selectivity and ability to differentiate from other resident microflora. Generally, the numbers of inoculated Aeromonas sp. recovered on starch-ampicillin agar were similar to those recovered on brain heart infusion and blood ampicillin agar media, and were 10¹ to 10³ greater than the recovery rate on either MacConkey-ampicillin or cefsulodinirgasan-novobiocin agars. The sensitivity for the direct recovery of Aeromonas sp. from inoculated beef feces with naturally contaminating microflora, using streaked starch-ampicillin agar medium, was between 10² and 10³ cells per gram. Using starch-ampicillin agar, the incidence of Aeromonas detected from feces of beef, pig, sheep and turkey held at the Beltsville Agricultural Research Center was one of 32, none of 22, none of 24 and three of 21, respectively. Based upon current taxonomic criteria, the isolate from the beef feces had characteristics consistent with both Aeromonas sobria and Aeromonas caviae , whereas three isolates from turkey feces were identified as A. caviae or Aeromonas hydrophila . The organism was isolated from five of five packages of ground beef from retail sources. The discrepancy in the consistent presence of the organism in retail meat suggests that many of the food isolates are probably not of fecal origin.