Antibiotic Bactericidal Activity Is Countered by Maintaining pH Homeostasis in Mycobacterium smegmatis

Abstract

Since the discovery of antibiotics, mortality due to bacterial infection has decreased dramatically. However, infections from difficult to treat bacteria such as Mycobacterium tuberculosis and multidrug-resistant pathogens have been on the rise. An understanding of the cascade of events that leads to cell death downstream of specific drug-target interactions is not well understood. We have discovered that killing by several classes of antibiotics was stopped by maintaining pH balance within the bacterial cell, consistent with a shared mechanism of antibiotic killing. Our findings suggest a mechanism of antibiotic killing that stems from the antibiotic’s ability to increase the pH within bacterial cells by disrupting proton entry without affecting proton pumping out of cells. Knowledge of the core mechanism necessary for antibiotic killing could have a significant impact on the development of new lethal antibiotics and for the treatment of recalcitrant and drug-resistant pathogens.

Genetic and metabolic regulation ofMycobacterium tuberculosisacid growth arrest

“…A hallmark of metabolically active, non-replicating states is the development of phenotypic tolerance to antibiotics and stress [9,12,34,35]. A role of acidic pH in promoting antibiotic tolerance by preventing cytosolic alkalinization has been previously shown in Mycobacterium smegmatis [36]. The sensitivity of Mtb to isoniazid, rifampin, and the detergent sodium dodecyl sulfate (SDS) was measured to test whether acid growth arrest was associated with phenotypic drug or stress tolerance.…”

Antibiotic efficacy — context matters

“…Under anoxia, nitrate frequently participates in anaerobic respiration as the terminal electron acceptor and can potentiate antibiotic killing [33]; it is not yet known if nitrate and other terminal electron acceptors also generate toxic metabolic byproducts that contribute to antibiotic death processes. Cellular respiration likely affects antibiotic efficacy due to its roles in metabolism and energy production, but may also contribute to lethality by facilitating drug import [37,71] or stimulating intracellular alkalization [72]. Collectively, these studies implicate respiratory activity as an important mediator of the lethal processes induced by antibiotics.…”

A macrophage-based screen identifies antibacterial compounds selective for intracellularSalmonellaTyphimurium

“…In this strain, we were unable to isolate spontaneous resistance mutants after several attempts plating at 4xMIC (observed frequency of resistance <4.8 x 10 −10 ). Recently, it has been proposed that antibiotic-induced bacterial cell death can be partially attributed to an imbalance in proton homeostasis across the inner membrane 32,33 . Moreover, previous work suggested that the antifungal activity of metergoline against Candida krusei was due to depolarization of the mitochondrial membrane potential and induction of reactive oxygen species 34 .…”