The presence of Aeromonas, Listeria and Yersinia in carcass processing equipment at two pig slaughtering plants

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Skinned pork loins and equipment at two pig slaughtering plants were examined for the presence of yersiniae, aeromonads and listeriae. Using enrichment techniques, Aeromonas hydrophila and/or Aeromonas caviae were isolated from each of 24 loins sampled at each plant. Listeriae, two of which were Listeria monocytogenes , were isolated from 23 of 24 loins at plant A, but from only one of 24 loins at plant B. Yersiniae were not recovered from the loins at either plant. Homogeneates of swabs or solid samples, rinse waters and machine waters were directly plated onto selective agars. Aeromonads were recovered from most samples from equipment at both plants, but their numbers in dehairing equipment were lower at plant B than at plant A. Listeriae were recovered from most samples from breaking equipment at plant A, but were recovered from only one sample from those equipment items at plant B. Yersiniae were recovered sporadically, and generally in small numbers, from equipment at both plants, with their recovery being more frequent at plant A than plant B. The different recoveries of the various organisms at the two plants were attributable to the operating temperature of the dehairing equipment being higher at plant B than at plant A, and to better cleaning of the carcass breaking equipment at plant B.