Assessment of disinfectant performance against fish-pathogenic bacteria in planktonic and biofilm states

Disinfecting fish farming equipment and facility surfaces with disinfectant is one of the primary biosafety measures to prevent disease introduction and transmission. However, the actual efficacy of approved disinfectants against fish-pathogenic bacteria and especially their biofilms remain largely undocumented. Six selected disinfectants were evaluated against seven common disease-causing bacteria and their biofilms. None of the tested disinfectants exhibited good efficacy against Mycobacterium salmoniphilum (the log reductions were ≤ 3.3). Two disinfectants showed low efficacy against Pseudomonas fluorescens in comparison to other tested bacteria, log reduction ≤ 4. Among three bacterial biofilms, good efficacies were only observed against the biofilm of Aliivibrio wodanis with 100% biofilm viability reduction for all disinfectants. Reduced disinfectant efficacy was observed for the biofilms of Yersinia ruckeri (97.4 - 100%) and P. fluorescens (> 99%). The study underscores significant gaps in disinfectant performance against fish pathogens, particularly Gram-positive species and suggests that bacterial biofilm formation can substantially compromise disinfection efficacy.