Food Protection Trends - September 2008 - 654

TABLE 2. Prevalence and concentration of S. aureus on chilled carcasses at plants A–E Baseline 3 Plant n Prevalence (concentration*) n Present survey Prevalence (concentration*) Beef A B Sheep C D E 71 30 30 17.0 (1.90) 63.3 (1.50) 43.0 (1.30) 25 25 25 80 (1.0) 32 (1.23) 20 (0.84) 41 31 58.5 (0.97) 51.6 (1.06) 25 25 0 0 *Mean log10 count/cm2 of positive samples portation to an ISO17025-accredited laboratory for testing. Upon arrival at the laboratory, samples were held at 2–4°C until examination, which was always on the day after sampling. plate for coagulase testing with BHI broth and then rabbit plasma. S. aureus on freshly exposed surfaces after punching and final inspection At the “punching” station the operator separates a small area of fleece at each shoulder, called a “pocket,” then plunges his fist downwards to separate the fleece from underlying tissue. The process is called “pocket and punch” and involves the operator plunging his fisted hand and arm beneath the fleece at least to his elbow. After the fleece on each side has been punched, the operator pulls back on the fleece to release it from shoulder to rump. In the present study, the punched area on each side of the freshly exposed carcass was sponged immediately after the operator had completed pull-back. The S. aureus count was determined on a total of 15 carcasses; the organism was isolated from all carcasses mean log 0.45 log CFU/cm2 and varying -0.08 to 1.0 log CFU/cm2. At plant C, it was noted that carcasses were inspected at the end of the process by two operators, neither of whom wore gloves. Inspection involved significant handling of the rump and hind legs as operators turned, held and palpated the body during inspection. To adduce whether S. aureus had been transferred during inspection, carcasses were transferred to the retain rail and the entire hindquarters were sponged to a level just below the tail. Ten carcasses were sampled and S. aureus was isolated from RESULTS AND DISCUSSION S. aureus on beef and sheep carcasses In Table 2 are presented summary data for prevalence and concentration of S. aureus on chilled carcasses at five plants, selected because of the high prevalence of S. aureus on their carcasses as established in Baseline 3. In the interim, at beef plants A and B disposable gloves had been introduced and were worn by all operators at the time carcasses were sampled in the present study. As indicated in Table 2, S. aureus was not detected on any of the 25 samples from each plant, compared with over 50% prevalence in Baseline 3. At sheep plants D and E, disposable gloves are optional but were worn by a majority of operators, and this may be responsible for the reduction in prevalence and concentration of S. aureus in the present study, compared with Baseline 3. At plant C gloves were worn by all slaughter floor operators except for those involved in freeing the fleece by manual punching, and by staff at final inspection. Prevalence was much higher in the present survey than in Baseline 3, although the concentrations were lower. Accordingly, further investigation was undertaken to estimate contamination incurred at punching and final inspection. Determination of Total Viable Count (TVC), E. coli and coagulase-positive staphylococci Buffered peptone water (25 ml) was added to the sponge bag, which was squeezed by hand 10 times. Serial dilutions were prepared in 0.1% peptone water, using 1 ml aliquots. For TVC, duplicate Petrifilm plates (3M, Sydney, Australia) were prepared according to method AOAC 990.12 and incubated at 35oC/48 h, after which the colonies were counted and the count/cm2 recorded. Generic E. coli were estimated by placing 1ml aliquots of both the initial solution and appropriate dilutions onto duplicate E. coli Petrifilm (3M, Sydney, Australia) and incubating at 35oC for 48 h. Colonies were counted as per the manufacturer’s instructions and AOAC method 991.14. Coagulase-positive staphylococci on carcasses were determined using Australian Standard method AS1766.2.4, in which 0.5 ml aliquots were spread onto dried plates of Baird Parker agar (Merck, Melbourne, Australia) and incubated at 37°C for 48 h. Colonies with typical morphology (grey-black, shiny, convex colony with a narrow entire margin surrounded by a zone of clearing) were picked off the 654 FOOD PROTECTION TRENDS | SEPTEMBER 2008

Food Protection Trends - September 2008

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