Temperature, Disinfectant Concentration and Bacterial Innate Properties Influence the Disinfection of Bacterial Pathogens Relevant to Catfish Aquaculture

Aquaculture systems suffer a wide range of losses, mostly due to bacterial disease outbreaks, and the use of disinfectants is a routine practice for controlling the spread of pathogenic organisms globally. Including Aeromonas hydrophila, Streptococcus agalactiae and Edwardsiella tarda, implicated for natural disease outbreaks and economic losses in catfish culture systems. Unfortunately, suboptimal disinfection practices are widespread within catfish aquaculture systems, and information on the factors influencing disinfection efficacy is limited. In this study, the efficacy of Virkon aquatic disinfectant against pathogenic strains of A. hydrophila, S. agalactiae and E. tarda was investigated by measuring changes in absorbance and viable colony counts at 22°C, 28°C and 34°C. The in vitro assays were conducted via broth microdilution suspension and carrier test methods to investigate the influence of disinfectant concentration, strain variation and temperature fluctuations on disinfection efficacy within catfish aquaculture systems. The results revealed that 0.125% was the MIC and MBC for the S. agalactiae strains under all the experimental conditions in both tests. However, at 28°C and 34°C, the MIC and MBC were 0.25% for A. hydrophila strains in the suspension test and 0.5% for the carrier test. Among all the strains, E. tarda presented the highest level of resistance to the disinfectant, with 1% MBC in the carrier test at 22°C and 28°C. In addition, the MIC value for strains of A. hydrophila and E. tarda was 0.25% at 28°C and 34°C in the suspension test, and both species had the same MBCs of 0.25% at 28°C in the suspension test and 0.5% at 34°C in the carrier test. Overall, changes in temperature, disinfectant concentration and intrinsic bacterial factors were identified as the principal factors that influenced the disinfection efficacy of Virkon aquatic disinfectant. Our findings identified suboptimal sanitation practices as high aquaculture biosecurity risk and emphasized that the carrier test is an ideal method for evaluating the efficacy of chemical disinfectants applied in the context of aquaculture.