Effect of three commonly used aquaculture chemicals against enteropathogenic Escherichia coli and Salmonella spp.

Abstract

Enteric bacteria such as Escherichia coli and Salmonella spp. are significant fish pathogens and related to thousands of cases of food-borne diseases every year in human. Since aquatic environments are reservoirs of these pathogens, they may contaminate the food fish and result in outbreaks. Therefore, it is crucial to reduce or eliminate these pathogens from aquaculture facilities. We tested effectiveness of three commonly used aquaculture chemicals, viz., lime, hydrogen peroxide and zeolite on bacterial load, Escherichia coli and Salmonella spp. under laboratory and earthen pond conditions where they were applied at a dose recommended for freshwater aquaculture. Results of the bacteriological study showed that lime had a significant role in reducing bacterial abundance from an initial value of 1.5 × 103 to 1.9 × 103 cfu/ml and 3.9 × 103 to 6.3 × 103 to a final value of 1.2 × 103 to 1.5 × 103 cfu/ml and 1.9 × 103 to 6.3 × 103 cfu/ml within 24 h under aquaria and pond condition, respectively. A complete inactivation of E. coli was observed in lime treated aquaria and ponds 24 h post-treatment, whereas Salmonella spp. remained unaffected in pond water but inactivated under aquarium condition after same period. However, neither hydrogen peroxide nor zeolite treatment reduced total bacterial count as well as E. coli and Salmonella even after 1-week post-treatment. It is, therefore, recommended that the water treatment chemicals should be applied in aquaculture ponds at appropriate dose, and farmers need to adopt biosecurity measures to ensure food safety.