"Quaternary ammonium compounds (QACs) are a group of antimicrobials extensively used in homes, hospitals, industrial and agricultural facilities for disinfection and sanitization purposes since 1930s. Many studies have shown that exposure to QACs leads to the selection of intrinsically resistant bacteria in a microbial community or results in the development or acquisition of resistance mechanisms. In addition, connection of antibiotic resistance, which is becoming one of the most pressing problems for human and environmental health, to the unconstrained use of antimicrobials such as QACs is, recently, under serious criticism.QACs are lytic biocides, capable of killing over 99% of microorganisms at typical application concentrations. However, certain microorganisms that are resistant and capable of QAC degradation are present. Relatively recently, a study revealed that not only QACs but also many other antimicrobials and antibiotics are degraded by native microorganism which are potentially pathogenic in the environments critical for human and environmental health. This discovery elicits several questions: “Is biotransformation an antimicrobial resistance mechanism?” and “What is the role of biotransformation in the dissemination of antimicrobial resistance in the environment?”. The answers may have important implications on the human health, but these answers have not been given yet.Biotransformation, whether acting as a resistance mechanism or not, plays a significant role in the fate of antimicrobial agents, and therefore, affects the dynamics of antimicrobial resistance in the environment. The overall objective of the proposed research is to systematically assess: (a) the role of QAC biotransformation on the QAC resistance of a microorganism; and (b) the dynamics of the survival of microorganisms and development of QAC resistance during QAC exposure in a community having microorganisms with different tolerance and biotransformation capacity for QACs."