Biofilm Formation on Aquaculture Substrates by Selected Bacterial Fish Pathogens

The objective of this study was to determine whether common bacterial catfish pathogens could attach and colonize surfaces commonly found in aquaculture facilities. In addition, we evaluated the role of calcium in biofilm formation. Attachment to polystyrene plates was used to quantify biofilm formation by five bacterial pathogens (i.e., Flavobacterium columnare, Aeromonas hydrophila, Edwardsiella ictaluri, E. tarda, and E. piscicida). Flavobacterium columnare and A. hydrophila formed thick biofilms that were enhanced by calcium supplementation. Biofilm formation was significantly lower in all Edwardsiella species tested and calcium had little to no effect on Edwardsiella biofilm formation. Attachment to natural and artificial surfaces was quantified by a standard plate count method. Scanning electron microscopy (SEM) was used to confirm biofilm formation on the substrates. Flavobacterium columnare formed biofilm on the liner, flexible PVC, and nets. Bamboo prevented F. columnare attachment and inhibited cell growth. Aeromonas hydrophila and E. ictaluri formed biofilm on all materials tested, although significant differences were found among substrates. While E. ictaluri failed to form biofilm on microtiter polystyrene plates, it was able to colonize and multiply on all aquaculture materials tested. Our results demonstrated that common bacterial pathogens had the potential of colonizing surfaces and may use biofilm as reservoirs in fish farms.