Effectiveness of different methodologies for the selective enumeration of Lactobacillus acidophilus La5 from yoghurt and Prato cheese

Abstract

Prior to the selective enumeration of probiotic microorganisms in fermented dairy products, a preliminary evaluation of different culture media and incubation conditions is required to choose a suitable culture medium. The objective of this study was to evaluate the effectiveness of different methodologies for the selective enumeration of Lactobacillus acidophilus in probiotic yoghurt and Prato cheese. For selective enumeration of L. acidophilus, four methods were investigated under anaerobic conditions, as follows: MRS agar containing bile solution; MRS agar containing clindamycin solution; and MRS agar containing sorbitol solution, each one incubated at 37 °C for 72 h, and MRS agar containing sorbitol incubated at 45 °C for 72 h. These methodologies were used for enumeration of both the pure cultures and the microorganisms from probiotic yoghurt and Prato cheese. The results showed that the best selective medium for enumeration of L. acidophilus from yoghurt was MRS agar containing bile incubated at 37 °C for 72 h under anaerobic conditions. For enumeration of this probiotics from Prato cheese, MRS agar containing sorbitol incubated at 45 °C for 72 h under anaerobic conditions was proven to be the best selective medium.