As shown in Table 4, Lactococcus lactis strains were able to grow
in MRSB and MRS + S media in high counts. This can lead to the
statement that the MRSB and MRS + S media were not selective for
L. acidophilus La5 in the presence of L. lactis in Prato cheese. The
addition of 1.5% bile to the culture medium was not able to inhibit
L. lactis. Although the sensitivity of lactococci strains to bile salts is
reported in literature, this characteristic is strain dependent, which may explain the variability in
results using this culture medium for different microorganisms. In
contrast, the addition of bile in MRS agar was able to inhibit the
yoghurt starter culture, thus being considered selective for
enumeration of L. acidophilus from these products (Table 3). Based
on experimental results, we conclude that the high counts in the
Prato cheese (>9.0 log CFU/mL) when the culture media MRSB and
MRS þ S were used, have probably included Lactococcus lactis
strains, and may have also included other microorganisms such as
NSLAB. This conclusion was supported by colony morphology and
microscopic observations (data not shown). also
observed the non-selectivity of MRS-S for enumeration of
L. acidophilus from cheese.