The replacement of glucose by sorbitol in MRS agar should
inhibit the development of the lactic acid bacteria, since these
microorganisms cannot ferment sorbitol, such as S. thermophilus
strains (Hardie & Whiley, 2006). However, this behavior was not
verified in this study, since pure cultures of Lactococcus lactis, L.
bulgaricus and S. thermophilus have developed in the culture medium
containing sorbitol at 37 C (L. lactis) or 45 C (yoghurt cultures).
Possibly the unusual growth of these strains in the presence
of sorbitol could be explained by culture rotation, which is a
technique performed by several industrial manufacturers of cultures
in order to control bacteriophages. The inhibition of Lactococcus
lactis in MRSS agar incubated at 45 C suggests that the
incubation temperature was responsible for the lack of development
in this medium as Lactococcus lactis does not grow at 45 C