Project Summary: Bacterial pathogens in water pose a large world-wide threat to public health,especially for the population with weak immune system. While current disinfection strategies aimat mitigating the presence of pathogens, they do not completely eradicate the growth ofmicroorganisms. This raises a question as to what happens to the surviving microorganisms afterdifferent disinfection processes. It is still unclear that if these surviving microorganisms are thesame, less or more hazardous than the ones before disinfection. The answer to that question hasa significant impact on microbial safety. As regards effective disinfection, what really matters isreduction of pathogenicity instead of the concentration of microorganisms. The long-term goalis to gain a better understanding on pathogenicity and susceptibility to antibiotics of survivingmicroorganisms after disinfection and elucidate the role of regulatory defense systems ofsurviving microorganisms. The proposed research project seeks to reveal the characteristicvariations of bacteria before and after different disinfection processes by conducting systematicstudy to provide guidance regarding disinfection strategies. The primary objectives of thisproposal will be achieved by addressing the following specific aims: Specific Aim 1. Investigatemicrobial community structure and functions in raw and treated water after various disinfections.Specific Aim 2. Determine the virulence and antibiotic resistance of surviving bacteria afterdisinfections. Specific Aim 3. Elucidate the role of disinfectants in horizontal gene transfer ofantibiotic resistance genes and virulence factors. Achieving the above aims will providefundamental knowledge on the characteristics of surviving bacteria after disinfections which isvital to public health. The enhanced knowledge will facilitate the development of novel disinfectionstrategies to reduce the pathogenicity of surviving bacteria and minimize the spread of bacteriawith virulence and antibiotic resistance into water. These studies will also benefit the future R01grant, where we will explore the correlations between disinfectant strategies and pathogenicity ofsurviving microorganisms and elucidate the role of regulatory defense systems of survivingmicroorganisms.