Out of the many TAS described, the relBE family is one of the most abundant, being present in the three first sequenced strains of Streptococcus pneumoniae (D39, TIGR4 and R6).
http://plosone.org/article/info:doi/10.1371/journal.pone.0011289#article1.front1.article-meta1.abstract1.p1

Streptococcus pneumoniae is a human pathogen causing nearly 2,000.000 deaths per year. The bacteria carry several chromosomally-encoded toxin-antitoxin systems (TAS). One of them, termed relBE2Spn is abundant in other bacteria and archaea. The relE2Spn gene specifies a toxin, which is neutralized by the binding of its cognate RelB2Spn antitoxin. We show here that a strain harbouring a mutation in the relBE2Spn operon exhibited a different behaviour, compared to the wild type strain, when challenged by conditions that impaired protein synthesis. The relBE2Spn system may be triggered under these stressful situations and, depending upon the inhibitor selected to arrest protein synthesis, it would either adapt bacterial growth to the stress or mediate cell death. We performed an exhaustive search for the presence of this TAS in S. pneumoniae. This search showed that the relBE2Spn, unlike its E. coli homolog, is present in all the 100 pneumococcal strains checked. In spite of the high genetic diversity exhibited by pneumococci (due to the frequent homologous and illegitimate recombination, the so-called hyper-recombination status), the RelBE2 module has been kept functional, suggesting that it could provide the bacteria with advantages that force its functional conservation in the pneumoccocal genome.