Principles of creation dental plaque, transmission of bacteria inductive dental caries or presence of mutant streptococci at infectious endocarditis are the actual research areas, in which modern molecular-biological methods can be used. The aim of the paper is to clear up the mechanisms of the methods which are applied in identification of bacteria (such as restriction analysis, sequencing, PCR). Polymerase chain reaction (PCR) is a progressive method by which we can amplify the definite part of the nucleotide chain in vitro. Sequencing analysis of DNA is the most exact (but not the easiest) technique for comparison of congeniality of organisms.

        Key words: streptococci – PCR – RFLP – DNA