In one aspect, this disclosure describes a pharmaceutical composition that generally includes frankiamicin A and a pharmaceutically acceptable carrier. In another aspect, this disclosure describes a method of treating a subject having, or at risk of having, a condition caused by a microbial infection treatable with frankiamicin A. Generally, the method includes administering to the subject an amount of frankiamicin A effective to ameliorate at least one symptom or clinical sign of the condition.