The spread of antibiotic resistance is a growing global challenge that is estimated to be directly responsible for around 1.3 million deaths each year worldwide. Certain groups of bacteria produce spores, a hardy cell form whose persistence and transmission properties have been implicated in the spread of antibiotic resistance genes 1,2. However, the interplay between antibiotic resistance genes and spore biology is poorly understood. Spores of the human and animal pathogen Clostridioides difficile are a crucial driver of disease dissemination, initiation, and re-infection. We previously showed that cephamycin antibiotics can inhibit spore formation in C. difficile epidemic isolates by targeting the spore-specific penicillin binding protein CdSpoVD 3. Here, we show that acquisition of a penicillin binding protein, CdMecA, by C. difficile strains blocks spore inhibition by cephamycins, uncovering a unique mode of antibiotic resistance. CdMecA is prevalent in 9.8% of 10,000 C. difficile genomes surveyed and can be found amongst both gut and environmental bacterial spore-formers. Spore resilience and germination studies revealed differences in phenotypic properties between wild-type CdSpoVD spores and cephamycin-induced CdMecA spores. The fifth-generation cephalosporin, ceftobiprole, can target CdMecA, and in combination with the cephamycin cefotetan restored inhibition of spore formation. Our work shows for the first time how an acquired antibiotic resistance gene can unexpectedly, and directly, modulate spore formation, highlighting the detrimental impact of antibiotic overuse in healthcare and animal production environments.