Fumarate-Mediated Persistence of Escherichia coli against Antibiotics

Abstract

g Bacterial persisters are a small fraction of quiescent cells that survive in the presence of lethal concentrations of antibiotics. They can regrow to give rise to a new population that has the same vulnerability to the antibiotics as did the parental population. Although formation of bacterial persisters in the presence of various antibiotics has been documented, the molecular mechanisms by which these persisters tolerate the antibiotics are still controversial. We found that amplification of the fumarate reductase operon (FRD) in Escherichia coli led to a higher frequency of persister formation. The persister frequency of E. coli was increased when the cells contained elevated levels of intracellular fumarate. Genetic perturbations of the electron transport chain (ETC), a metabolite supplementation assay, and even the toxin-antitoxin-related hipA7 mutation indicated that surplus fumarate markedly elevated the E. coli persister frequency. An E. coli strain lacking succinate dehydrogenase (SDH), thereby showing a lower intracellular fumarate concentration, was killed ϳ1,000-fold more effectively than the wild-type strain in the stationary phase. It appears that SDH and FRD represent a paired system that gives rise to and maintains E. coli persisters by producing and utilizing fumarate, respectively. Bacterial persisters are phenotypic variants that are tolerant even to supralethal concentrations of multiple antibiotics (1-3). Reseeding of the persisters yields a bacterial population with a frequency of antibiotic-tolerant cells that is similar to that of the parental population (4, 5). Persisters are distinct from antibioticresistant cells because the ability to tolerate antibiotics is neither genetically determined nor inherited. Persisters showing tolerance of different classes of antibiotics are observed in most microbial species and have been implicated in chronic and recurrent infections (1). Furthermore, it is highly probable that persisters are a potential reservoir for the development of drug resistance in pathogenic bacteria (6, 7).Despite the discovery of bacterial persisters more than 70 years ago (4), the mechanisms that underlie noninheritable persistence phenotypes remain unclear. Various researchers recently identified a number of genes and pathways that lead to persister formation or survival upon antibiotic treatments. These include toxinantitoxin (TA) modules, a stringent response, phosphate metabolism, alternative energy production, and antioxidative defense (8-13). Because nongrowing or slow-growing bacteria are less sensitive to antibiotics, dormancy has been proposed to be the mechanism of last resort in many of these persistence studies. Thus, many recent mechanistic studies have focused on how bacterial cells reach the dormant state (8-15). Nonetheless, the prevailing hypothesis that persisters might survive solely because of dormancy is being challenged. A lack of significant growth or metabolic activity does not guarantee persistence, and dormancy is neither necessary nor sufficient fo...

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Understanding and Sensitizing Density-Dependent Persistence to Quinolone Antibiotics

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Inactivation of TCA cycle enhances Staphylococcus aureus persister cell formation in stationary phase

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