The expression of six enterotoxin geneswas monitored at 12, 16,
20, 28 and 48 h of TSB and milk cultures (Fig. 2). Sampling intervals
in the following expression study were chosen according to the
determined growth patterns. The first samplewas taken at 12 h (the
exponential growth phase) prior to SEC production and the decrease
in pH. The next sampling pointwas at 16 h (late-exponential growth
phase) when the SEC production started to be quantifiable. The 20 h
meant the transition between the exponential and stationary
growth phase in addition to the initial change of pH. The following
two sampling points (28 and 48 h) symbolized the early and late
stationary phase of growth. During the growth of MW2 increasing
expression of the enterotoxin genes C, H and L was observed in TSB
compared to milk, whereas constant expression levels were
observed for the enterotoxin genes A, G and K.