Low Dose Exposure to Disinfectants Causing Co-Resistance to Antibiotics for Bacteria in Aquaculture Settings

Low dose disinfectants such as ChloramineT, Ozone and Hydrogen Peroxide, are commonly used in aquaculture to treat surface bacterial infections on fish, and to reduce the bacterial levels in the water to avoid systemic infections, which need to be treated with antibiotics. The use of disinfectants has been advocated as a means of reducing the use of antibiotic drugs, but research is suggesting that these biocides may select for coresistance to antibiotics in bacterial populations. The mechanism(s) for this coresistance may be multifold. In some cases it may be driven by the selection and or up regulation of genes involved in efflux pump modulation or cell wall permeability. In one of our studies, we incidentally found bacteria with these genes were observed to dominate the microbial population after low ozone treatments; however, we did not evaluate the population for antibiotic resistance after the treatment. Given the frequency of the use of low dose disinfectants in aquaculture it is important to determine if this practice is exacerbating the issue of antibiotic resistance. We proposed to evaluate the impact of disinfectants on the resistance of a fish pathogen (Aeromonas hydrophila). We will use a laboratory model with this bacteria and oxytetracycline, a commonly used antibiotic in aquaculture, to understand the underlying mechanisms for the co-resistance. As well we propose to assess the effect of disinfectant treatments on the broader microbial community in fish farms in Hong Kong. The findings of this research may highlight a significant issue with a very common management strategy in aquaculture, which needs to be address if we are to improve the sustainability of fish farming in Asia.