LACTIC-ACID BACTERIA OF FOODS AND THEIR CURRENT TAXONOMY

Application of molecular genetic techniques to determine the relatedne ss of food-associated lactic acid bacteria has resulted in significant changes in their taxonomic classification. During the 1980s the genus Streptococcus was separated into the three genera Enterococcus, Lacto coccus and Streptococcus. The lactic acid bacteria associated with foo ds now include species of the genera Carnobacterium, Enterococcus, Lac tobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Strepto coccus, Tetragenococcus, Vagococcus and Weissella(1). The genus Lactob acillus remains heterogeneous with over 60 species (ymol% G + C conten t ranging from 33 to 55), of which about one-third are strictly hetero fermentative. However, many changes have been made and reorganization of the genus along lines that do not follow previous morphological or phenotypic differentiation from Leuconostoc and Pediococcus is being s tudied. Phylogenetically belonging to the Actinomyces branch of the ba cteria, Lactobacillus bifidus has been moved to the genus Bifidobacter ium also on account of its greater than 50 mol% G + C content. It is t herefore no longer considered one of the lactic acid bacteria sense st rictu, which form part of the Clostridium branch of the bacteria. The new genus Weissella has been established to include one member of the genus Leuconostoc (Leuc. paramesenteroides) and heterofermentative lac tobacilli with unusual interpeptide bridges in the peptidoglycan. Cont rary to the clear-cut division of the streptococci, morphological and physiological features of Weissella do not directly support this group ing which now incorporates species that produce D(-)- as well as DL-la ctate. The new genus Carnobacterium is morphologically similar to the lactobacilli, but it shares some physiological similarities (e.g. grow th at pH 9.5) and a common phylogenetic branch with the genus Enteroco ccus. The review includes information on the taxonomic changes and the relationship of the bacteria to food fermentation and spoilage. (C) 1 997 Elsevier Science B.V.