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Whole dry-cured (country-style) hams from six manufacturers were sliced and the slices randomly allotted into five treatment groups per manufacturer. One treatment group served as a control and slices in the four other treatment groups were inoculated with approximately 10 5 CFU/g of ham of either Escherichia coli O157:H7, Listeria monocytogenes , a mixture of three Salmonella spp. ( Salmonella typhimurium , Salmonella enteritidis and Salmonella choleraesuis ), or Staphylococcus aureus . All ham slices were vacuum-packaged with half of the packages in each treatment group stored at 25°C and half stored at 2°C. Two packages from each manufacturer for each treatment and storage temperature were examined after storage for 0,7, 14,21, and 28 days. S. aureus was detected in 2 of 60 control slices, Salmonella in 2 of 120, L. monocytogenes in 4 of 120, and E. coli O157:H7 was not detected in any of the 120 control ham slices analyzed before or after storage. Aerobic (26 and 35°C) populations of the control vacuum-packaged hams slices increased ( P < 0.05) with storage time and the increase in populations was greater ( P < 0.05) in vacuum-packaged hams slices at 25 than at 2°C. The extent of the decreases in populations of the inoculated pathogens during storage of vacuum-packaged dry-cured ham slices varied with manufacturer ( P < 0.05) and storage temperature ( P < 0.05). Decreases in Salmonella spp. and E. coli O157:H7 populations were greater ( P < 0.05) in slices stored at 25 than at 2°C, while decreases in L. monocytogenes were similar at both storage temperatures. Staphylococcus aureus enterotoxin was not detected in either S. aureus -inoculated or control ham slices after storage for 28 days. Survival of these pathogens in vacuum-packaged dry-cured ham slices suggests that contaminated hams may pose a safety risk to consumers if consumed without adequate cooking.

A total of 1,137 samples representing 77 cook-chill food products were analyzed during a 27-month period. Vacuum-packaged food samples from the same production batch of regular diets or products modified for low sodium, low fat, diabetic, or strained diets were analyzed before and after storage at 1 ± 1°Cfor up to 21 days in a hospital's food bank. Samples were analyzed for aerobic counts at 26°C and 35°C and for coliforms, staphylococci, Bacillus cereus , Clostridium perfringens , Escherichia coli , E. coli O157:H7, Listeria spp., Salmonella spp. and Staphylococcus aureus . None of the samples contained C. perfringens , E. coli , E. coli O157:H7, or Salmonella . Listeria was isolated from one production batch of asparagus which had been inadequately heated and cooled due to overloading of the vat. S. aureus was isolated (<100 CFU/g) from 2 samples (beef roast, stewed tomatoes) and B. cereus was isolated (<100 CFU/g) from several pasta and bean products. Low-fat products had higher ( P < 0.05) aerobic populations than products modified for low sodium, low fat, diabetic, or strained diets. No differences were obtained between the before- and after-storage populations. Over 92% of the samples had aerobic populations of 3 log CFU/g or less and 98% had populations of 4 log CFU/g or less. All except 2 samples had coliform populations of 1 log CFU/g or less and all samples had staphylococci populations of 3 log CFU/g or less. Under the conditions of this study, the microbial quality of vacuum-packaged foods properly produced by an enhanced cook-chill system was acceptable after food storage at 1 ± 1°Cfor up to 21 days.

Thirty-three biochemical characteristics were compared for 855 staphylococci isolated from human (93) and bovine sources (762). Differences in the predominant Staphylococcus species present and biochemical characteristics of species were observed for isolates from bovine milk and human clinical sources as well as between milk isolates obtained during the 1960s and 1980s from the same herd. All isolates were bacitracin-resistant and 98% were lysostaphin-sensitive. Approximately 31% of S. hyicus strains were coagulase-positive. Thermonuclease activity was observed for strains other than S. aureus . Milk strains were more salt tolerant than human strains. Carbohydrates tended to be utilized by a greater percentage of milk strains than human strains within a given species. Many milk isolates failed to utilize glycerol in the presence of 0.4 μg erythromycin/mL. The results of this study indicate that the source of isolates may influence the predominant species present and species biochemical characteristics. These differences in species characteristics may affect results obtained for identification of nonhuman isolates with rapid identification systems where the data bases are generally based on human clinical isolates.