Attachment of bacteria to beef from steam-pasteurized carcasses

The extent to which a bacterial cocktail containing equal numbers of Pseudo monas fragi NCTC 10689, Listeria monocytogenes BL5/2, Salmonella Typhimuriu m LT2, and Escherichia coli JM 109 attached to loin surface cuts (7 by 5 cm ) derived from steam-pasteurized beef carcasses has been evaluated. The ext ent of attachment was categorized as loosely attached (removed by rinsing), firmly attached (released by stomaching), and irreversibly bound. No signi ficant difference (P > 0.10) in the attachment of bacteria to steam-pasteur ized carcasses was found compared with control loin samples that had receiv ed no treatment. No significant difference (P > 0.05) was also found in the attachment strength between the different bacterial species tested. Most b acteria inoculated onto the loin cuts were reversibly bound, since they had been removed by rinsing and stomaching. The irreversible attachment of bac teria to loin cuts was found to vary significantly (P < 0.01) among the dif ferent carcass sets used but was independent of whether the carcass had und ergone steam pasteurization treatment. Use of a bioluminescent strain of E. coli showed that cells bound preferentially to cut edges and convoluted ar eas on the loin surface and could not be removed by rinsing. The possible m echanisms of bacterial attachment and the suitability of steam pasteurizati on to remove contamination incurred during slaughter are discussed.