Mehta Heer H, Ibarra David, Marx Christopher J, Miller Craig R, Shamoo Yousif
Department of Biosciences, Rice University, Houston, TX, United States.
Department of Biological Sciences, University of Idaho, Moscow, ID, United States.
Front Microbiol. 2022 May 9;13:904822. doi: 10.3389/fmicb.2022.904822. eCollection 2022.
Combination antimicrobial therapy has been considered a promising strategy to combat the evolution of antimicrobial resistance. is the causative agent of tularemia and in addition to being found in the nature, is recognized as a threat agent that requires vigilance. We investigated the evolutionary outcome of adapting the Live Vaccine Strain (LVS) of subsp. to two non-interacting drugs, ciprofloxacin and doxycycline, individually, sequentially, and in combination. Despite their individual efficacies and independence of mechanisms, evolution to the combination arose on a shorter time scale than evolution to the two drugs sequentially. We conducted a longitudinal mutational analysis of the populations evolving to the drug combination, genetically reconstructed the identified evolutionary pathway, and carried out biochemical validation. We discovered that, after the appearance of an initial weak generalist mutation (FupA/B), each successive mutation alternated between adaptation to one drug or the other. In combination, these mutations allowed the population to more efficiently ascend the fitness peak through a series of evolutionary switch-backs. Clonal interference, weak pleiotropy, and positive epistasis also contributed to combinatorial evolution. This finding suggests that the use of this non-interacting drug pair against may render both drugs ineffective because of mutational switch-backs that accelerate evolution of dual resistance.
联合抗菌疗法被认为是对抗抗菌药物耐药性演变的一种有前景的策略。土拉弗朗西斯菌是兔热病的病原体，除了在自然界中被发现外，它还被视为一种需要警惕的威胁因子。我们研究了土拉弗朗西斯菌亚种的活疫苗株（LVS）分别、依次以及联合适应两种非相互作用药物（环丙沙星和强力霉素）后的进化结果。尽管这两种药物各自有效且作用机制相互独立，但向联合用药的进化比依次向两种药物的进化在更短的时间尺度上发生。我们对向药物联合进化的群体进行了纵向突变分析，从基因上重建了所确定的进化途径，并进行了生化验证。我们发现，在出现最初的一个较弱的通用突变（FupA/B）后，后续的每个突变在适应一种药物或另一种药物之间交替。这些突变共同作用，使群体能够通过一系列进化折返更有效地登上适应度峰值。克隆干扰、弱多效性和正向上位性也促成了组合进化。这一发现表明，使用这对非相互作用药物对抗土拉弗朗西斯菌可能会因加速双重耐药性进化的突变折返而使两种药物都失效。
