Roles of water quality and disinfectant application on inactivation of fish pathogenic Streptococcus agalactiae with povidone iodine, quaternary ammonium compounds and glutaraldehyde.

Streptococcosis is an important bacterial disease in Nile tilapia causing severe economic losses to tilapia aquaculture worldwide. The effects of water quality (low- [LS] and high-level [HS] soiling, to mimic clean or dirty surface conditions and temperatures) and disinfectant application (diluted concentrations and exposure time) were characterized on the inactivation of Streptococcus agalactiae isolated from diseased tilapia. Five isolates were tested against three commercial disinfectant products with the main ingredients being povidone iodine (Anidine 100™; AD), benzalkonium chloride (Better BKC 80%™; BKC 80), and a mixture of quaternary ammonium compounds and glutaraldehyde (Chloraldehyde™; CR). CR demonstrated highest efficacy to S. agalactiae inactivation, followed by BKC 80 and AD, respectively. Higher-level soiling, low temperature, diluted concentrations and short exposure time all decreased the disinfectant efficacy. CR and BKC 80 provided more than 5-log inactivation at 1-min exposure at 20°C under HS conditions, and also with ten-fold-diluted concentrations at 60-min exposure time at 30°C. However, AD required 10-min exposure to effectively remove bacteria under LS conditions at 30°C. The results could facilitate aquaculture management planning that leads to operating cost reductions and improvements in biosecurity.