SUMMARY Deployment of new antimicrobials is promptly circumvented by the rapid evolution of resistance, underscoring the critical need for new strategies to stay ahead in the arms-race against bacterial pathogens. Developing a detailed understanding of the circumstances as well as genetic and mechanistic basis for which antibiotic resistance develops provides opportunities for pre-emptively subverting this process. While infections caused by organisms harboring antimicrobial resistance (AMR) genes are a major cause of antibiotic treatment failure (ATF), ATF frequently occurs when the etiological agents are not AMR by traditional susceptibility testing. It is becoming increasingly recognized that transient cell-states such as tolerance, persistence and hetero-resistance are critical drivers underlying treatment failure. However, there is a paucity of data with regards to the genetic and mechanistic basis for these cell-states as well as a lack of diagnostic-detection approaches. ATF cell-states initially exist as minority variants within a population and display a transient phenotype that tends to dissipate as the stress subsides, making them challenging to detect and consequently missed in current diagnostic assays. These enabler cell-states remain mechanistically poorly understood and seem to preferentially arise during fluctuating treatment regimens, for instance caused by a drug’s PK/PD characteristics, whereby ATF cell-states can drive the re-emergence of the (susceptible) bacterial infection after antibiotic pressure wanes. Importantly, this creates opportunities where multi-step high-level resistance mutations are given an extended opportunity to emerge. Therefore, because antibiotic resistant variants often follow closely on the heels of the occurrence of ATF cell-states, these cell-states can be viewed as enablers of antibiotic treatment failure and AMR. This proposal focuses on untangling the importance of ATF cell-states in the emergence of antibiotic resistance and treatment failure, and designs new approaches and strategies to identify, track and target them. The main team consists of 4 principal investigators that have a very successful collaboration history. Together they will work on 5 challenges distributed across 3 projects and supported by an administrative and a genomics and bioinformatics core. In Challenge: 1) the full profile of possible genetic pathways that can induce ATF cell-states is determined; 2) treatment regimens that drive the emergence of ATF-cell states are determined; 3) it is determined how ATF cell-states enable the emergence of AMR; 4) drugs and compounds are screened for, that target ATF cell-state collateral sensitivities; 5) a computational deconvolution approach is developed that predicts the presence and frequency of ATF cell-states in a complex bacterial population. Overall this proposal contains a collection of conceptually and technically innovative aspects that are geared towards understating the gen...