LAB Screening for pH and Bile-Salt Tolerance
Thirty-seven out of the 150 tested LAB isolates
showed tolerance to pH 3.0 during 3 h of incubation.
However, the growth in these conditions was not com-parable with that in conventional MRS (pH 6.5), with
reductions in counts at least 2 logarithmic units compared
with controls. These 37 isolates were tested by
a plate assay for resistance to different bile concentrations
ranging from 0.3 to 2%, and by tolerance in liquid
containing 0.3% of Oxgall. In the latter medium, a LT
ranging from 0.5 to 4 h was observed for 34 isolates
(Table 1); these were considered to be bile tolerant. In
contrast, 3 LAB isolates presented an LT >9 h; these
were considered bile susceptible.
As a result of the bile plate assay, 34 isolates grew in
0.3%, 25 grew in 0.5%, 13 in 1%, and 8 in 2% (Table 1).