Application of molecular methods for the classification and identification of lactic acid bacteria

Phylogenetic analysis has revealed that the typical lactic acid bacteria (LAB) belong to the Gram-positive bacteria with a low guanine cytosine 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 Enterococcus, Lactococcus, Streptococcus and Vagococcus. The traditional phenotypic identification of LAB is rather tedious and not always reliable. Nucleic acid probe technology may be an alternative for a faster and more reliable differentiation. 16S or 23S rRNA- targeted oligonucleotides have been used for the specific identification of LAB. It is even now possible to identify various LAB in fermented food, without any preceding enrichment or cultivation step, at the species level within one working day. Application of fluorescently labelled oligonucleotides also allowed the in situ detection and identification of whole cells of lactococci and enterococci. DNA restriction fragment analysis and 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 nucleic acids and the corresponding organisms.