The role of bacterial membrane potential in tuberculosis persistence and regrowth.

Importance: Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is the highest cause of mortality by a single infectious agent and kills 1.5 million people annually. Treatment of TB in humans is with lengthy, toxic, multidrug regimens and the increasing emergence of multidrug resistance (MDR) is a global concern. Mtb is able to evade T-cell clearance and enter a

physiological persistent state which is phenotypically resistant to antimicrobials. The ability of Mtb to enter into/exit from the persistent state compounds the problem of antimicrobial resistance. Background: Persistent states are not restricted to Mtb, many bacterial species the small colony variant (SCV) is associated with persistence. The clinical importance of SCVs is highlighted by their

isolation from patients with persistent, recurrent infections. SCVs show delayed growth anddefects in community behaviours such as biofilm formation and cell-cell signalling. Deficiencies in electron transport components such as haem are consistently described in SCVs suggesting an involvement for alterations in membrane potential. There has been a single description of an

SCV in Mtb which was observed from clinical samples and associated with antimicrobial resistance. An association between persistence, the occurrence of SCVs and antimicrobial resistance in mycobacteria is an understudied phenomenon. As part of an RVC PhD studentship (Faulkner 2017-2020) we silenced a putative haem synthase (HAS) in a non-pathogenic model of

Mtb (Mycobacterium smegmatis) and observed a SCV phenotype. In this project we explore this phenotype using a combination of molecular microbiology (Kendall, RVC), electrophysiology (Karlikowska and Stratford, Cytecom) and innovative mathematical modelling (Chang, RVC).