The success of any antibiotic or antimicrobial approach rests in the developer’s ability to demonstrate it can effectively kill bacteria or severely retard their growth. In addition, the success of a microbial therapeutic or probiotic product relies on knowing viable count. Correctly determining bacterial viability, in other words whether an individual cell is alive or dead, is a critical and challenging measurement. Our goal is to develop advanced methods for rapidly, accurately and quantitatively measuring the viability of mixed microbial populations. This project will focus on the development of systematic, reliable methods for measuring viability of individual cells in a population. Understanding the effect of sublethal dosing chemical, antibiotic or UV antimicrobial treatments on viability and pathogenicity is critical insight that will help drive the success of real-world antimicrobial technologies. General approaches may include advanced imaging modalities, high-throughput technologies, standards and reference material development, and validation against existing compendial methods. The development of techniques to quantify viability will provide the means to reliably screen mixed microbial populations in vitro.