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Comp Immunol Microbiol Infect Dis. 2013 Mar;36(2):199-209. doi: 10.1016/j.cimid.2013.01.001. Epub 2013 Feb 13.

Connection of toxin-antitoxin modules to inoculation eschar and arthropod vertical transmission in Rickettsiales.

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Aix Marseille Université, URMITE, UM63, CNRS 7278, IRD 198, Inserm 1095, 13005 Marseille, France.


The biological role of toxin-antitoxin systems (TAS) in pathogenicity and cell addiction of Rickettsia was recently reported. We realized a comparative genomic analysis onto 33 rickettsial genomes and correlated the presence of TAS encoding genes with vertical transmission (VT) in arthropod hosts, the presence of inoculation eschar in humans and experimental animals, and the mortality in humans. There is a significant statistical link between TAS and the presence of an eschar (p≤0.0001). The presence of TAS is also significantly inversely correlated with mortality. The toxic effect of TAS may increase the local reaction, thus inhibiting the spread of rickettsiae associated with fatal outcome of the disease. The TAS were also linked to VT (p≤0.0001). Together with our previous findings we speculate that this is the first addiction system evidenced in intracellular bacteria. Thus, the TAS, as selfish genetic elements, might be essential to the evolutionary strategy of intracellular bacteria.

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