Development of a miniaturized selective counting strategy of lactic acid bacteria for evaluation of mixed starter in a model cassava fermentation

Abstract

A minaturized most probable number (MPN) method for the selective enumeration of three bacteria species (Lactobacillus plantarum A6, Leuconostoc mesenteroides and Lactococcus lactis) is described. This selective count method, based on specific consumption of carbon substrate and resistance to antibiotics, was used for the quantitative assessment of the three bacteria during mixed cultures in a model cassava fermentation. A typical microbial succession pattern was observed: (i) Lactococcus lactis and Leuc. mesenteroides dominated during the first hours of fermentation as their growth was very rapid; (ii) from hour 12, Lactobacillus plantarum replaced the two latter strains and Lactococcus lactis disappeared gradually, followed by Leuc. mesenteroides. The growth rates of each strain appeared to be independent of the others, while acidification rates increased strongly in mixed cultures compared with pure cultures. No positive interactions resulting from the amylolytic character of Lactobacillus plantarum A6, and no negative interactions resulting from the Nis+ property of Lactococcus lactis, were revealed between the three strains under the model conditions used.