부산대학교 도서관

ABSTRACTScrub typhus is a potentially lethal infection caused by the obligate intracellular bacterium Orientia tsutsugamushi. Reports on the emergence of doxycycline-resistant strains highlight the urgent need to develop novel antiinfectives against scrub typhus. Corallopyronin A (CorA) is a novel α-pyrone compound synthesized by the myxobacterium Corallococcus coralloidesthat was characterized as a noncompetitive inhibitor of the switch region of the bacterial RNA polymerase (RNAP). We investigated the antimicrobial action of CorA against the human-pathogenic Karp strain of O. tsutsugamushiin vitroand in vivo. The MIC of CorA against O. tsutsugamushiwas remarkably low (0.0078 μg/ml), 16-fold lower than that against Rickettsia typhi. In the lethal intraperitoneal O. tsutsugamushimouse infection model, a minimum daily dose of 100 μg CorA protected 100% of infected mice. Two days of treatment were sufficient to confer protection. In contrast to BALB/c mice, SCID mice succumbed to the infection despite treatment with CorA or tetracycline, suggesting that antimicrobial treatment required synergistic action of the adaptive immune response. Similar to tetracycline, CorA did not prevent latent infection of O. tsutsugamushiin vivo. However, latency was not caused by acquisition of antimicrobial resistance, since O. tsutsugamushireisolated from latently infected BALB/c mice remained fully susceptible to CorA. No mutations were found in the CorA-binding regions of the β and β′ RNAP subunit genes rpoBand rpoC. Inhibition of the RNAP switch region of O. tsutsugamushiby CorA is therefore a novel and highly potent target for antimicrobial therapy for scrub typhus.