Examination and Evaluation of the Persistence of Virulent Aeromonas hydrophila, Edwardsiella ictaluri and Flavobacterium covae Within the Sediments of West Alabama Commercial Catfish Ponds

Abstract

The three most prevalent bacterial pathogens responsible for channel (Ictalurus punctatus) and hybrid [♀ channel catfish (I. punctatus) × ♂ blue catfish (I. furcatus)] catfish losses are virulent Aeromonas hydrophila (vAh), Edwardsiella ictaluri and Flavobacterium covae. Substantial progress has been made regarding management and treatment practices for these bacterial diseases. However, recurring and chronic infections caused by these pathogens continue to cause significant economic losses annually. One aspect of bacterial pathogenesis that has yet to be studied in detail is determining if virulent A. hydrophila, E ictaluri, and F. covae can persist within the bottom sediments of commercial catfish ponds. In a laboratory setting, three separate persistence trials were conducted, each using three 37 L glass aquaria divided into four separate chambers containing sterile sediment from commercial catfish ponds, disinfected water, and known vAh, E. ictaluri and F. covae inoculum concentrations of 1.64 × 108, 8.33 × 107, and 1.78 × 107 colony forming units (CFU) per mL, respectively. One gram of sediment was extracted on specified sampling days, and serial dilutions of suspended homogenized sediments were plated onto selective media to enumerate bacterial colonies and monitor CFU g-1 of bacteria in sediments. After all persistence trials were completed, it was determined that vAh and E. ictaluri persisted in this environment, whereas F. covae did not survive. Interestingly, vAh and E ictaluri populations experience initial growth across all sediments, then plateau after 14- and 5-days post-inoculation, respectively. Future research projects are necessary to determine which environmental factors can influence population changes in these pathogenic bacteria over time and allow them to persist within the sediments of commercial catfish ponds.