Although none of the tested probiotic strains grew in MRS broth
at pH 2.0, all strains were able to grow in MRS broth pH 4.0. After
48 h of incubation in MRS broth adjusted to pH 4.0, 94% (16/17) of
the strains showed >50% growth and 65% (11/17) of the strains
showed >75% growth compared to standard MRS broth. Growth in
MRS broth at pH 4.0 ranged between 44 and 90% compared to
growth in standard MRS broth at pH 6.8. Seven of the seventeen
(41%) strains were delayed in growth showing only 1e40% of
growth at 24 h and 57e93%at 48 h. When MRS broth was supplemented
with 0.15% bile, all strains showed >75% growth after 48 h
of incubation. Growth in MRS broth with 0.15% bile ranged between
56 and 99% at 48 h compared to growth in standard MRS broth.
When adding 0.3% bile, 16/17 (96%) strains showed >50% growth
after 48 h and 11/17 (65%) showed >75% growth after 48 h. Strainspecific
growth data of selected probiotic strains that showed
inhibitory activity against both C. difficile and C. perfringens are
presented in Table 3