Quantitative analysis of growth of Escherichia coli in co-culture with Lactococcus lactis subsp. lactis in milk

Abstract

The growth of the Escherichia coli strain isolated from lumpy goat cheese was studied in milk and in co-culture with Lactococcus lactis subsp. lactis. The strain in mono-culture showed very good rate of growth in milk, reaching the numbers higher than 8 log CFU/ml during the stationary phase at all the tested temperatures. The minimal growth temperature of 9.5 °C was determined from secondary mathematical equation (GrEc = 0.0327*T - 0.3101; R2 = 0.9755). Primary modelling of the growth curves of two competitive organisms showed that only L. lactis inoculum of 107 CFU/ml at temperature from 18 to 21 °C could suppress the growth of E. coli and keep its numbers during stationary phase at maximal density of 104 CFU/ml. Combined effect of the initial inoculation of L. lactis and incubation temperature on E. coli was described with the highly significant second order equation: Gr_Ec_Lc = 0.02104 + 0.000693*T2 – 0.000727*T*N0_Lc; (R2 (µ) = 0.98).