Potassium sorbate (PS), sodium nitrate (SN), condensed phosphate, sodium chloride, and glycine, added singly or in combinations, to Brain Heart Infusion (BHI) at different pH values were examined for the inhibitory effects on growth and enterotoxin A production of Staphylococcus aureus (S. aureus) in inoculum sizes of 103 and 106 cells/ml and at 35°C. Only a slight inhibition of S. aureus was observed at pH 5.0 and aw0.99, and it decreased as pH was raised to 6.0 and 7.0. Some inhibitory effects of PS were seen at 1, 000 ppm and 2, 000 ppm inoculated with 103 and 106 cells/ml of S. aureus at pH 5.0, respectively and 20, 000 ppm at pH 6.0 and 40, 000 ppm at pH 7.0 and aw 0.97 on the both inocula. Growth and enterotoxin production of S. aureus were inhibited by SN of 75 ppm with the inoculum of either size at pH 5.0, but was not controlled by the addition of 750 ppm SN at pH 6.0. Sodium acid pyrophosphate (SAPP) at 4, 000 ppm was not effective on S. aureus at any pH, but sodium ultrapolyphosphate (SUPP) and sodium metaphosphate (SMP) at 4, 000 ppm were very effective on the both inocula at pH 7.0. Sodium tripolyphosphate (STPP) and a 2: 1 mixture of STPP and SAPP (TPAP) at 4, 000 ppm inhibited growth and enterotoxin production of S. aureus on the inoculum of either size at pH 5.0, and on the inoculum of 103 cells/ml at pH 6.0, respectively. STPP at 2, 000 ppm was effective on the inoculum of 103 cells/ml of S. aureus. The combination of 200 ppm of PS and 35 ppm of SN at pH 5.0 and 2, 000 ppm of PS and 35 ppm of SN at pH 5.5 exhibited a synergistic activity on the both inoculums of S. aureus. The combination of 75 ppm of SN and 2, 000 ppm or 1, 000 ppm of TPAP at pH 6.0 also showed clear inhibition on the both inocula and on the inoculum of 103cells/ml of S. aureus, respectively. At pH 6.5, 75 ppm of SN and 4, 000 ppm of TPAP showed a effective inhibition on the inoculum of either size. The combination of three agents, 2, 000 ppm of TPAP, 75 ppm of SN, and 2, 000 ppm of PS showed a high effect more rapidly in about 12 hours than without PS at pH 6 .0 on S. aureus. When NaCl was further supplemented, growth was slightly inhibited, especially by the addition of 3.5% NaCl that has got up speed about 8 and 16 hours when inoculated with 103 and 106 cells/ml of S. aureus, respectively. At pH 6.5 and aw 0.95, growth and enterotoxin production of S. aureus in BHI inoculated with 103cells/ml were completely inhibited by the combination of 3, 000 ppm of TPAP, 75 ppm of SN, 1, 000 ppm of PS, 3.5% of NaCl and 1% of glycine after 72 hours of incubation.
A synthetic medium for the production of trichothecene mycotoxins by Fusarium species has been developed. Fusarium sporotrichioides F-135 strain was inoculated in a synthetic medium (SSA) containing sucrose, salts, asparagine and Ca-panthothenate. In 14 days of still incubation at 25°C, the organisms produced 2, 265μg/ml of T-2 toxin and 420μg/ml of diacetoxyscirpenol. The medium also supported production of a large amount of fusarenone X, nivalenol, neosolaniol, butenolide and moniformin by the organisms. The results indicate that the SSA medium appears to be suitable for production of trichothecens and other mycotoxins by Fusarium species. The medium consists of the following components: sucrose 200g, Asparagine 10g, Capanthothenate 0.01g, NaNO3 1g, MgSO4·7H2O 1g, KH2PO4 0.75g, ZnSO4·7H2O 0.1g, FeSO4·7H2O 0.01g, MnCl2·4H2O 0.001g, CuSO4·5H2O 0.001g, Co (NO3) 2·6H2O 0.0001g, NaMoO4·2H2O 0.001g, NiCl2·6H2O 0.001g, Na2B4O7 0.001g and distilled water 1, 000ml.
The effect of low pH on survival and growth of C. jejuni and C. coli were studied in Brain Heart Infusion broth acidified with hydrochloric, acetic, citric, maleic, succinic, malic or lactic acid. The survival and growth of C. jejuni and C. coli at low pH depended in the type of acid present. The cells of C. jejuni and C. coli died within 3 h at pH 4.0 adjusted with each organic acid at either 10 or 25°C. In broth adjusted to pH 5.0 with lactic or acetic acid, the cells decreased in number within 24 h and 48 h, respectively, at 10°C. At pH 5.0 adjusted with other acids and at 10°C, the cells survived over 48 h. The cells of C. jejuni held for 48 h at 25°C decreased in number in broth adjusted to pH 5.5 with any organic acid. C. jejuni and C. coli grew at pH 5.7 acidified with hydrochloric, citric, succinic, malic or lactic acid; however they failed to grow at the same pH value acidified with acetic or malic acid. The lowest pH at which C. jejuni and C. coli grew in these acids was 6.5.