Staphylococcus aureus의 增殖과 enterotoxin産生에 미치는 pH, 溫度 및 食品添加物의 影響

Effect of pH, temperature and food additives on staphylococcal growth and enterotoxin production

In this study, field isolates of Staphylococcus aureus from the fresh chicken carcasses and from the pathological lesions of chickens with staphylococcosis were subjected to determine the growth characteristics and the immunological toxin types. In addition, effective food additives were screened to inhibit the growth and enterotoxin production of S. aureus in order to promote the food safety. When one hundred and twenty fresh chicken carcasses obtained from 6 poultry processing plants at Kyong-gi area from March to November in 1990 and chicken specimens diagnosed as staphylococcosis during 4 years from 1989 to 1992 were examined, total of 83 and 106 strains of S. aureus isolated, respectively. Among those, 4 of 83 isolates from the fresh chicken carcasses, and 74 of 106 strains from chickens with staphylococcosis were typed as enterotoxigenic strains of S. aureus, respectively. All these enterotoxigenic strains produced an enterotoxin type D only, and these enterotoxins from the 48 strains tested all caused an emetic response in cat. To determine the production of staphylococcal enterotoxin, 10 isolates and 4 reference strains(ATCC 13565, 14458, 19095 and 23235) of S. aureus were inoculated into NZ-medium at a concentration of 10⁴ cells/ml and incubated at various temperature. At 10℃, all fourteen strains did not grow and produce enterotoxins until 240 hours. At 15℃, 3 strains(ATCC 13565, 14458 and 1 isolate) produced an enterotoxin after 72 hours of incubation, and 8 strains(ATCC 23235 and 7 isolates) produced after 96 hours of incubation, respectively. Nevertheless the remaining 3 strains(ATCC 19095 and 2 isolates) did not produce unitl 96 hours. At 37℃, eleven out of 14 strains produced enterotoxin after 4 to 7 hours of incubation, and each 1 strain produced after 8, 9 and 10 hours, respectively. When ground chicken meats inoculated with S. aureus were incubated at 22℃, all 14 strains produced enterotoxin in the raw meat after 24 hours of incubation, and 12 strains produced enterotoxin in the heated meat(100℃, 30 minutes) after 6 to 12 hours. When 21 food additives were tested for inhibitory effects on the growth and enterotoxin production of S. aureus in brain heart infusion broth, butyl p-hydroxybenzoate(BH), butylated hydroxyanisole(BHA) and lactic acid(LA) showed a significant inhibitory effects. The lower pH of media, the greater inhibiotry effects of BH, BHA and LA were observed. In addition, a combination of BH or BHA with NaCI had a greater inhibitory effect than when either BH or BHA were used alone. Complete inhibition of S. aureus growth occured in BHI broth with 156.3ppm BH or 200ppm BHA. In combination with 2% NaCI, however, 100ppm BH or 150ppm BHA exerted bacteriocidal effects. The bacteriocidal effect was also observed when 0.4% LA was supplemented in the culture medium. When 0.2% LA, 0.2% sorbic acid, 25ppm BH+2% NaCI, 25ppm BHA+2% NaCI, or 0.15% erythorbic acid+0.26% potassium sorbate+0.01% sodium nitrite+2% NaCI were added to raw chicken meat production of enterotoxin from the inoculated S. aureus was completely inhibited until 48 hours of storage at 22℃.