DECONTAMINATING BEEF FOR ESCHERICHIA-COLI O157-H7

Beef lean, fat, and connective tissues were inoculated with Escherichi a coli O157:H7 before and after a prewashing procedure to compare the efficacy of prewashing and no prewashing on bacterial adherence and, c onsequently, on the removal of bacteria from the inoculated surfaces. Prewashing consisted of spraying tissues with tap water before inocula tion. Final washing with disinfectant solutions compared the efficacy of several chemicals for the removal or destruction of E. coli O157:H7 . The results showed that prewashing was very effective in reducing th e numbers of bacterial cells on beef tissues, mainly lean tissue, in t he control samples which received final washing with water. An opposit e effect of prewashing was observed when disinfectant solutions were u sed for final washing; this may be due to dilution by water carried on the tissues after prewashing. The efficacy of chemicals was dependent on the type of exposed tissue. Hydrogen peroxide (3%) was more effici ent in the removal of E. coli O157:H7 from connective tissues, with re ductions greater than 4 log CFU/cm(2), compared to a normally washed c ontrol (P < 0.01). Chlorhexidine (0.1%) was very efficient on fat and lean tissues, causing reductions over 5 log CFU/cm(2) on not prewashed fat and lean tissues, compared to the control (P < 0.01). Acetic acid (5%) was the least effective, decreasing the number of CFU by under 1 log/cm(2) as compared to the control; and no statistically significan t difference was found among tissues, even though the removal of bacte ria seemed less in lean tissue compared to fat or connective tissues.