The invention concerns a method for detecting by molecular identification a bacterium of one of the species of genus Streptococcus and four related genera Enterococcus, Gemella, Abiotrophia and Granulicatella which consists of using as probe or primer: the rpoB gene or gene fragment of one said bacterium of sequences SEQ ID no 1 to 3, or an oligonucleotide or mixture of oligonucleotides derived from sequences SEQ ID no 8 to 35, or in particular the oligonucleotides of sequences SEQ ID no 6 and 7.