Uncovering an alternate pathway of antibiotic resistance in spore-forming bacteria.

Spore-forming bacteria produce two distinct cell types: vegetative cells and resilient spores. While antibiotic resistance is typically associated with vegetative cells, spores play a critical role in disseminating resistance genes due to their durability and transmissibility. We previously demonstrated that cephamycin antibiotics target the conserved spore-specific protein SpoVD, significantly reducing spore formation in pathogens including Clostridioides difficile. Here, we show that when C. difficile acquires CdmecA, a homologue of Staphylococcus aureus mecA, one of the most globally burdensome resistance genes, the anti-sporulation effect of cephamycins is bypassed. CdMecA functionally replaces CdSpoVD, restoring sporulation and producing phenotypically distinct spores. We further show that mecA is prevalent across C. difficile strains and other pathogenic, gut, and environmental spore-formers. Since SpoVD is conserved, MecA may broadly co-opt sporulation; we confirm this in Clostridium perfringens. This work reveals an unusual resistance mechanism with unexpected physiological consequences, reshaping our understanding of antibiotic resistance within the context of sporulation and microbial adaptation.