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Abstract: 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. [ABSTRACT FROM AUTHOR]

This study investigated the effect of exposure times on the response of ammonia oxidizing mixed culture (AOMC) to phenolic compounds while having the future goal to develop a biosensor using AOMC for toxicity monitoring. AOMC was used instead of purified nitrifying culture because of the ease of culture development. The oxygen utilization rate (OUR) was measured during three exposure periods; 0-15, 25-40 and 50-65 min. It was found that phenolic compounds have a strong inhibitory effect on AOMC. The percentage of OUR reduction increased with higher concentrations and the extended exposure times improved the toxic response of AOMC, especially to the lower concentrations (0.25, 0.50, 1.0 mg/L). Further, AOMC detoxifying mechanisms might result in the reduction of toxic response when the longest exposure time was applied. However, at the higher concentrations (2.5 and 5.0 mg/L), the extended exposure times did not have a critical effect on the response pattern of AOMC, especially for phenol and mono-chlorinated phenols. It was illustrated that AOMC is very sensitive to phenolic compounds and its sensitivity is high enough for the detection of phenolic compounds at the level of effluent standard in Thailand and Japan with a rapid response time of 15 min. To improve the sensitivity of AOMC to low phenolic compound concentrations, an extended exposure time of 25-40 min would be recommended. [ABSTRACT FROM AUTHOR]