Competitive effect of lactic acid bacteria on growth of Staphylococcus aureus

Abstract

In connection with ewe’s lump cheese production, the inhibiting potential of two mesophilic cultures of lactic acid bacteria was described. The initial amount of lactic acid bacteria necessary for keeping the growth of Staphylococcus aureus under control were estimated in ultra-pasteurized milk. The growth inhibition of S. aureus 2064 with mesophilic culture Fresco was more effective when the higher addition of competitive microflora and the lower incubation temperature were used. At a temperature of 25 °C, Staphylococcus aureus 2064 at stationary phase reached counts higher than 106 CFU/ml by the Fresco culture addition N0_Fr = 2.95 log10 counts and by the addition of Fresco N0_Fr = 6,6 log10 in the beginning there was an increase of about 1 log in staphylococci counts. At a temperature of 18 °C, comparable addition of Fresco culture (N0_Fr = 6.7 log10 counts) could increase the S. aureus count only at about 0.53 log. Increase of S. aureus 2064 in stationary phase against its initial numbers in co-culture with Fresco culture at 25 °C was determined using the equation Nmax_Sa - N0_Sa = - 0.7258N0_Fr + 5.6748 (R2 Nmax_Sa - N0_SA = 0.9281). The behaviour of Staphylococcus aureus 2064 and mesophilic culture A at a temperature of 25 °C was also studied. The culture A showed similar, even higher inhibitory effect on S. aureus growth at 25 °C. In this case, the growth of S. aureus 2064 in co-culture with culture A at 25 °C was described by the equation Nmax_Sa - N0_Sa = -2.1814N0_A + 12.605 (R2 Nmax_Sa - N0_Sa = 0.9564). The duration of pH lag-phase, hence the time during which no changes of pH values were observed was determined by initial inoculum of Fresco culture at each incubation temperature. These dependencies were described by statistically significant linear relations in this work. The maximal increase of S. aureus counts at stationary phase by 1 log against its initial numbers was controlled by the addition of the Fresco culture or the mesophilic A culture higher than 106 CFU/ml or 105 CFU/ml, respectively.