Distribution and sources of microbial contamination on beef carcasses

Three beef dressing lines of different capacity (160, 440 and 800 head d-1) were investigated with respect to contamination associated with carcass/hide and carcass/faeces contacts, the distribution of microbial contamination on carcasses and the antimicrobial efficacy of cold water carcass washes. Swab samples were taken from up to 17 sites for determination of Aerobic Plate Counts at 37 degrees C (APC 37 degrees C) and Escherichia coli enumeration using the Petrifilm procedure. The three beef dressing systems produced virtually identical patterns of microbial contamination. High contamination was found at those sites associated with opening cuts and/or subject to hide contact during hide removal. Where contamination is intermittent, the use of mean microbial data tended to obscure evidence of faecal or hide contact. Consequently, worst-case results, as represented by the 95th percentile value, were used to identify probable instances and sources of contact contamination. Sites not subject to faecal contamination or hide contact typically had swab sample APC (37 degrees C) values of less than log 2(.)00 cfu cm-2 accompanied by the occasional detection of E. coli at levels below log 1(.)00 cfu cm-2. Sites contacted by 'clean' hide typically had APC (37 degrees C) counts of log 3(.)00 cfu cm-2 or greater accompanied by occasional E. coli counts not exceeding log 2(.)00 cfu cm-2. Sites contaminated by direct faecal contact or contact with faecally contaminated hides typically had APC (37 degrees C) counts equal to, or greater than, log 4(.)00 cfu cm-2 accompanied by E. coli counts exceeding log 2(.)00 cfu cm-2. Cold water carcass washing was ineffective in removing microbial contamination and tended to bring about a posterior to anterior redistribution, resulting in increased counts at forequarter sites.