GRAVES, R. R. (Uniiversity of Wiscoinsin,-Madison), AND W. C. IXRAZIER. Food microorganisms influencing the growth of Staphylococcus aureus. Appl. MIicrobiol. 11:513-516. 1963. Some 870 cultures of predominating microorganisms were isolated from market samples of hamburger, fresh pork sausage, fresh fish fillets, stewing beef, frozen chicken pot pie, frozen corn, frozen peas, and pasteurized and raw milk, before and after storage at different temperatures. The isolates were screened for their ability to influenice the growth of Staphylococcus aureus strain 196E by means of spot-plate tests on AlT and nutrient agars at 25 C. The 438 cultures that influeniced the growth of S. aureus were retested on spot plates at 15, 30, and 42 C. After elimination of replicates, the 143 remaining cultures were classified into species, genera, or groups, and 14 differenit cultures were tested for their influence on the growth of S. aureus in APT broth at 23 C. Over half of the effective cultures inhibited S. aureus and less than half were stimulatory. Pork sausage had the highest proportioni of inhibitory cultures, arid stewing beef had the lowest. APT agar was better than nutrient agar for screening, and incubationi at 15 C gave more effector organisms than at 30 and 42 C. .\Iost of the lactic acid bacteria were inhibitory,

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Over a period of 4 years, 770 low-acid canned food spoilage incidents were investigated to determine the cause of spoilage. In 27 of these, the cause was attributed to the growth of bacteria of the Clostridium genus that had entered the cans as a result of post-processing leakage. No correlations were found that might explain the occurrence of this mesophilic anaerobic type of spoilage. It appears to be a random event, probably linked to cannery insanitation. A variety of species was found, consisting of both proteolytic and non-proteolytic types. Clostridium botulinum was not isolated from any of the canned foods examined, nor were any of the samples found to contain botulinal toxin. Container leak test methodology and principles are discussed.

I Fifty-nine samples of can-cooling water from 30 midwestern canneries were examined for aerobic plate count, salmonellae, coagulase-positive staphylococci, coliforms, enterococci, and mesophilic aerobic and anaerobic (putrefactive) spores including spores of Clostridium botulinum. No Salmonella or C. botulinurn were detected. Indicator bacteria counts were low with nearly 75% of the samples showing MPN levels of

The microbial flora of fresh, unsterile, dough products held at refrigeration temperatures was compared with the microbial flora of the same products that had spoiled spontaneously. Various methods based on selective media were used to determine molds, yeasts, and bacteria present. Except for two special cases in which a yeast and Penicillium roqueforti induced spoilage, all of the samples deteriorated because of bacterial growth. A total of 1,132 bacterial isolates was subjected to further classification. In the spoiled products, 92% of the isolates belonged to the Lactobacillaceae. More than one-half of these (53%) belonged to the genus Lactobacillus, and an additional 36% were in the genus Leuconostoc. In the genus Leuconostoc almost all of the strains (94%) were L. mesenteroides. The third most common genus present was Streptococcus, represented by 3% of the total isolates. A preliminary taxonomic study of the microflora of refrigerated dough products revealed none of the isolates to be indicators of fecal contamination and none to be forms known to produce toxins. The highest counts encountered in the moist, fresh products were up to 200 million lactic acid bacteria per g in buttermilk biscuits, with a psychrophilic count as high as 4.8 million. In the spoiled samples, the highest total counts were 820 million in buttermilk biscuits. Mold counts were no higher than 1,800, except in the sample ruined by P. roqueforti where the count was 130,000 mold colonies.

Some 870 cultures of predominating micro-organisms were isolated from market samples of hamburger, fresh pork sausage, fresh fish fillets, stewing beef, frozen chicken pot pie, frozen corn, frozen peas, and pasteurized and raw milk, before and after storage at different temperatures. The isolates were screened for their ability to influence the growth of Staphylococcus aureus strain 196E by means of spot-plate tests on APT and nutrient agars at 25 C. The 438 cultures that influenced the growth of S. aureus were retested on spot plates at 15, 30, and 42 C. After elimination of replicates, the 143 remaining cultures were classified into species, genera, or groups, and 14 different cultures were tested for their influence on the growth of S. aureus in APT broth at 25 C. Over half of the effective cultures inhibited S. aureus and less than half were stimulatory. Pork sausage had the highest proportion of inhibitory cultures, and stewing beef had the lowest. APT agar was better than nutrient agar for screening, and incubation at 15 C gave more effector organisms than at 30 and 42 C. Most of the lactic acid bacteria were inhibitory, but other groups of bacteria contained more stimulatory cultures than inhibitory ones. The three Escherichia coli cultures were stimulatory, but most other Escherichia cultures were inhibitory. Aerobacter and Paracolobactrum isolates were mostly stimulatory. Cultures of other kinds of bacteria were more or less evenly distributed between inhibitory ones and stimulatory ones. Genera containing mostly inhibitory bacteria were Streptococcus, Leuconostoc , and Lactobacillus . Inhibitory species were E. freundii and E. intermedia . Tests with S. aureus in broth indicated that all cultures inhibitory according to spot plates were inhibitory in broth, but stimulation on spot plates did not always indicate the same phenomenon in broth.

Microbiological surveys of post-processing can handling equipment were conducted in three low-acid food canneries to identify the source and numbers of mesophilic anaerobic sporeformers isolated from post-processing spoilage of cans packed at those canneries. Significant numbers of spores of these organisms were found on various equipment and can tracks. The spores were also isolated from the can cooling waters in two of the canneries and in numbers higher than have been reported previously. No correlation was noted between mesophilic anaerobic spore counts and total aerobic counts in samples obtained from the surveys. Clostridium botulinum was not isolated from any of the survey samples. A medium useful in the isolation of mesophilic anaerobic sporeformers is described.