Food Protection Trends - September 2008 - 653

TABLE 1. Prevalence and concentration of S. aureus on chilled beef (3) and sheep (4) carcasses, in frozen boneless beef (3) and sheep meats (4), and on chilled ground beef and diced lamb for retail sale (5) Beef Carcass Prevalence (%) Mean log10 CFU/cm2 or/g Standard deviation 90th percentile 95th percentile Maximum a Sheep Ground 28.1b 2.18 0.95 3.74 4.23 4.63 Carcass 23.4c 0.93 0.65 1.85 2.14 2.63 Boneless 32.7b 1.14 0.65 2.16 2.51 3.38 Diced 22.5b 2.34 0.86 3.63 4.02 4.48 Boneless 20.3b 0.80 0.32 1.00 1.74 2.32 28.7a 0.34 0.70 1.36 1.56 2.96 Limit of detection 0.08 CFU/cm2 Limit of detection 10 CFU/g b c Limit of detection 0.33 CFU/cm2 reports on the findings of the former investigation in abattoirs and boning rooms. water were used to sample each site of the selected carcass, a composite sample being taken by sponging a 100 cm2 area at each of the butt, flank and brisket regions of beef, and a 25 cm2 area at each of the midloin, flank and brisket of sheep, as detailed in the Mega Reg method (2). The third national baseline study of carcasses and boneless meat (3, 4) confirmed S. aureus on 15 and 20% of chilled sheep and beef carcasses, respectively, with concentration exceeding 2 log units CFU/ cm2 on some carcasses. On boneless beef and sheep meat, its prevalence was 2% and 16%, respectively, with mean concentration 1.5 log units CFU/g and 1.7 log units CFU/g, respectively. The first national retail study of red meat (5) similarly found high prevalence of S. aureus on ground beef and diced lamb samples. Although limits of detection differ, when the prevalence and concentration of S. aureus on carcasses, boneless meat and retail meat were compared (Table 1), significant (1–2 log units) increases in retail products became an issue that the industry considered should be investigated. The fact that S. aureus is perceived as a poor competitor against the spoilage microflora, coupled with its inability to multiply significantly at temperatures colder than 10°C (8), pointed toward either temperature abuse and/or excessive contact with the hands of food operators in the dressing-boning-retail continuum as causes of increased levels at retail. Accordingly, separate investigations were begun to locate sources of contamination with S. aureus at the abattoir/boning room and at the retail level. The present paper MATERIALS AND METHODS Design of the study Examination of data gathered in the third baseline study indicated that some processing operations produced meat with low prevalence and concentration of S. aureus while the reverse was obtained at others. Accordingly, an investigation was undertaken between October and November, 2006 at five abattoirs. At each, observations were made of how operators handled carcasses and meat cuts and samples were taken for microbiological analysis. Sampling of freshly exposed areas of sheep carcasses Using a Whirlpak sponge moistened as described above, a technician sponged each side of the freshly exposed carcass from immediately below the hindquarters to the brisket, using one side of the sponge for each half of the carcass. It was estimated that a total area of 3000 cm2 was sampled. Similarly, the entire hindquarters were sponged with one sponge to a level just below the tail; it was estimated that a total area of 1500 cm2 was sampled. Sampling of beef and sheep carcasses Selection of carcasses and subsequent sampling was performed by a team of trained technicians. Individual carcasses were selected for sampling by use of a systematic-random approach. Briefly, of the total lot of carcasses accessible to the technicians, one was sampled at regular intervals until the required number of carcasses was attained. Separate polyurethane sponges (Whirlpak speci-sponge, Nasco, USA) moistened with buffered peptone Direct plate sampling of the hands of operators Operators were requested to place the front and the back of each hand onto the surface of a Petri dish (14.5 cm diameter) containing Baird Parker Agar (BPA). Transport of samples to the laboratory All samples were packed in insulated containers with chiller packs for trans- SEPTEMBER 2008 | FOOD PROTECTION TRENDS 653

Food Protection Trends - September 2008

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