Comparing the results using the culture medium RCA pH 5.3 and
MRS at pH 5.2 (Table 4), we concluded that the components of RCA
are capable of inhibiting the growth of L. acidophilus and
S. thermophilus. In contrast, the decrease in pH of MRS agar to 5.2
was not sufficient to inhibit these microorganisms. Moreover, the
temperature and the conditions of incubation were the same for
both culture media, evidencing that the MRS agar at pH 5.2 was not
selective for the enumeration of L. bulgaricus from the probiotic
yoghurt under the conditions studied, since other strains that may
be present in yoghurt are able to grow in this culture medium.
Importantly, although literature reports different selective
methodologies for evaluation of microorganisms in probiotic
products, there is a need to test the culture media, once the
selectivity is directly related to the presence of other strains