APPLICATION OF MOLECULAR METHODS FOR THE CLASSIFICATION AND IDENTIFICATION OF LACTIC-ACID BACTERIA

Phylogenetic analysis has revealed that the typical lactic acid bacter ia (LAB) belong to the Gram-positive bacteria with a low guanine cytos ine DNA content. The genera Lactobacillus, Leuconostoc and Pediococcus can be traditionally differentiated on the basis of morphological and physiological properties but phylogentically they are intermixed. The former genus Streptococcus has been split up into the four genera Ent erococcus, Lactococcus, Streptococcus and Vagococcus. The traditional phenotypic identification of LAB is rather tedious and not always reli able. Nucleic acid probe technology may be an alternative for a faster and more reliable differentiation. 16S or 23S rRNA- targeted oligonuc leotides have been used for the specific identification of LAB. It is even now possible to identify various LAB in fermented food, without a ny preceding enrichment or cultivation step, at the species level with in one working day. Application of fluorescently labelled oligonucleot ides also allowed the in situ detection and identification of whole ce lls of lactococci and enterococci. DNA restriction fragment analysis a nd ribotyping have been used to distinguish LAB at the strain level or groups of closely related strains. Specific hybridization probes are also useful tools for the identification of genetically modified nucle ic acids and the corresponding organisms.