Antibacterial Activity of Acylglucinol Derivatives against Flavobacterium columnare

Abstract

Columnaris (caused by Flavobacterium columnare) is one of the most common bacterial diseases affecting the pond-raised channel catfish (Ictalurus punctatus) in the southeastern United States of America resulting in annual losses of millions of dollars. As part of our continuing effort to discover environmentally benign compounds for the control of columnaris disease, acyl derivatives of phloroglucinol were synthesized and tested against F. columnare using a rapid bioassay. Among the analogs that were tested, diacyl analogs showed very high antibacterial activity against F. columnare in the laboratory bioassay. Diisovaleryl and diisobutyryl analogs were found to have the strongest activity against F. columnare (isolate ALM-00-173) based on 24-h 50% inhibitory concentration (IC50) and minimum inhibitory concentration (MIC). Diisovaleryl and diisobutyryl analogs had IC50 values 0.82 mg/L and 0.80 mg/L, respectively, whereas the drug control florfenicol had an IC50 value of 0.81 mg/L. Diisovaleryl and diisobutyryl analogs also had 24-h relative-todrug-control IC50 values around 1.0 indicating activities similar to florfenicol, which is included in medicated feed and is one of the current management approach for columnaris.