Effect of polyphosphates on the behaviour of Staphylococcus aureus in bacteriological medium and in milk

摘要

The effect of different concentrations of polyphosphates (0.5, 0.4, 0.3, 0.1, 0.075, 0.05 and 0.025%) on growth of Staphylococcus aureus in an agar medium at 37℃ was investigated, as well as the effects of adding a 0.5% polyphosphate mixture on thesurvival of S. aureus in a nutrient broth at 4-6℃ and on the behaviour of S. aureus in milk at 4 and 20℃. Polyphosphates inhibited the growth of the S. aureus under investigation in agar medium at 37℃; growth of S. aureus was completely suppressed atpolyphosphate concentrations of _0.2%. S. aureus growth was significantly inhibited at polyphosphate concentrations of 0.1 and 0.075%, which produced bacterial counts of 0.6 X 101 and 2.4 X 104 respectively. Growth was affected only insignificantly by polyphosphate concentrations of 0.05 and 0.025%, where S.aureus counts of 5.1 X 106 and 7.1 X 106 respectively. This compares with a S. aureus count of 1.1 X 107 when no polyphosphate was added. When S. aureus was cultured in nutrient broth at 4-6℃, addition of a 0.5% polyphosphate mixture resulted in a reduced S. aureus count, at 5.9 X 105 after 6 days of incubation, compared with a count of 7.8 X 105 when cultured in broth without polyphosphate. A 0.5% polyphosphate solution also brought about a smallreduction in S. aureus numbers in milk at 4℃, although at a low level of significance. The inhibitory effect of addition of 0.5% polyphosphate on S. aureus growth in milk at 20℃ was insignificant.