There is a medical need for antibacterial agents that do not damage the resident gut microbiota or promote the spread of antibiotic resistance. We recently described a prototypic precision bactericidal agent, Av-CD291.2, which selectively kills specific Clostridium difficile strains and prevents them from colonizing mice. We have since selected two Av-CD291.2–resistant mutants that have a surface (S)-layer–null phenotype due to distinct point mutations in the slpA gene. Using newly identified bacteriophage receptor binding proteins for targeting, we constructed a panel of Avidocin-CDs that kills diverse C. difficile isolates in an S-layer sequence-dependent manner. In addition to bacteriophage receptor recognition, characterization of the mutants also uncovered important roles for S-layer protein A (SlpA) in sporulation, resistance to innate immunity effectors, and toxin production. Surprisingly, S-layer–null mutants were found to persist in the hamster gut despite a complete attenuation of virulence. These findings suggest antimicrobials targeting virulence factors dispensable for fitness in the host force pathogens to trade virulence for viability and would have clear clinical advantages should resistance emerge. Given their exquisite specificity for the pathogen, Avidocin-CDs have substantial therapeutic potential for the treatment and prevention of C. difficile infections.

对不损害常驻肠道微生物群或促进抗生素耐药性传播的抗菌剂存在医学需求。我们最近描述了一种原型精确杀菌剂 Av-CD291.2，它选择性地杀死特定的艰难梭菌菌株并防止它们在小鼠中定殖。由于slpA基因中的不同点突变，我们已经选择了两个具有表面（S）层无效表型的 Av-CD291.2 抗性突变体。使用新发现的噬菌体受体结合蛋白进行靶向，我们构建了一组 Avidocin-CD，可杀死多种艰难梭菌以 S 层序列依赖的方式分离。除了噬菌体受体识别，突变体的表征还揭示了 S 层蛋白 A (SlpA) 在孢子形成、对先天免疫效应物的抗性和毒素产生中的重要作用。令人惊讶的是，尽管毒力完全减弱，但发现 S 层缺失突变体仍存在于仓鼠肠道中。这些研究结果表明，针对宿主适应性可有可无的毒力因子的抗菌剂迫使病原体以毒力换取生存能力，并且如果出现耐药性，将具有明显的临床优势。鉴于其对病原体的高度特异性，Avidocin-CD 在治疗和预防艰难梭菌感染方面具有巨大的治疗潜力。