Infections associated with medicinal leech application are caused by Aeromonas hydrophila, an organism that resides in the leech gut. We cultured the intestinal tracts of 25 leeches and evaluated the efficacy of oral antibiotics against Aeromonas hydrophila. Cultures of this organism showed no sensitivity to ampicillin and inconsistent sensitivity to cephalothin (equivalent to cephalexin). The Aeromonas hydrophila cultures did show consistent sensitivity to ciprofloxacin, tetracycline, and trimethoprim-sulfamethoxasole. These three antibiotics should be considered if oral antibiotic coverage is used in association with leech application.