In vivo emergence of a still uncommon resistance to fidaxomicin in the urgent antimicrobial resistance threat Clostridioides difficile.

Although rarely reported, resistance to fidaxomicin may quickly emerge in vivo after a single course of treatment. This observation supports the need for prospective surveillance of the susceptibility of C. difficile to treatment antibiotics. However, the clinical relevance of fidaxomicin resistance still needs to be elucidated, particularly due to its apparent rareness and associated fitness cost.