The results of the selective enumeration of L. acidophilus from
yoghurt using different culture media are shown in Table 3. It was
observed that both MRSB and MRSC were selective for enumeration
of L. acidophilus, inhibiting the growth of L. bulgaricus and
S. thermophilus. For enumeration of L. bulgaricus, the medium RCA
pH 5.3 incubated at 45 C under anaerobic conditions was
considered effective, since the other cultures were inhibited under
these conditions. With respect to the enumeration of
S. thermophilus, ST agar incubated at 30 C under anaerobic conditions
was selective, since no growth of lactobacilli strains was
observed.
For the selective enumeration of L. acidophilus from Prato
cheese, the MRSS incubated at 45 C for 72 h under anaerobic
conditions was effectively selective, once it was observed development
of the pure culture of L. acidophilus and inhibition of Lactococcus
lactis (Table 4). For enumeration of Lactococcus lactis, M17
supplemented with lactose and incubated at 30 C under anaerobic
conditions was selective because only Lactococcus lactis strains
were able to develop in high counts under these conditions.