tRNA gene clusters at the 3' end of rRNA operons are specific to virulent subgroups of Streptococcus agalactiae strains, as demonstrated by molecular differential analysis at the population level.

The aim of this work was to characterize a 2.4 kb randomly amplified polymorphic DNA (RAPD) fragment described as a marker for a phylogenetic group of Streptococcus agalactiae strains significantly associated with neonatal meningitis. This fragment was analysed by cloning and sequencing, and showed that two types of tRNA gene cluster flank the 3' end of the rRNA operons in S. agalactiae strains. Both types of tRNA gene cluster act as markers for phylogenetic subgroups of strains within the species. One type could be used to distinguish two of the three virulent intraspecies subgroups to which most of the S. agalactiae strains able to invade the central nervous system of neonates belong. This raises the possibility that there is a link between these tRNA genes and the virulence of the bacterium. Based on this analysis, PCR primers were designed to determine whether S. agalactiae strains are likely to belong to lineages of organisms in which most of the highly virulent strains isolated from cerebrospinal fluid cluster. In addition, this work demonstrated that RAPD can be used to detect novel particularities within intraspecies variants of pathogens.