Persisters of Escherichia coli

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Antibiotic resistance and recalcitrant infections are challenges faced in the clinic every day. One perplexing aspect of this daily battle is the fact that many of these infections are caused by antibiotic susceptible bacteria, and yet cannot be cleared. The presence of persister cells in a bacterial population may explain these puzzling observations. Persisters are phenotypic variants that survive exposure to antibiotics, due to temporary dormancy. Therefore, understanding how persisters are formed can improve patient treatment. This research investigates persisters of Escherichia coli from several avenues. First we screened for a global regulator of persister formation. It has been demonstrated that fluctuations in expression of metabolic genes can affect persister formation, so we screened for a global regulator that creates global changes in the cell by controlling multiple genes in metabolism. We identified a deletion in ihfA which resulted in decreased persister levels when grown on various carbon sources. Further investigation revealed that ihfA was modulating persister formation through the glyoxylate bypass. Second, we investigated noise quenching of gene expression and its impact on persister formation. Persisters can form stochastically and noise in expression of metabolic genes has been shown to affect persister formation. We aimed to quench noise in a simple and defined system and examine the impact on persister formation. In a study of the inherently noisy lac operon, we determined that a deletion of lacI, the noise generating gene in the lac operon, had less persisters than the wild type. Finally, we interrogated the role of high persister (hip) mutations in vivo. Hip mutants have been identified in clinical isolates collected from patients, which suggests a link between persisters and clinical infection. We used an antibiotic-treated murine thigh infection model to assess the advantage, if any, hip mutants had in vivo. The data show that a hipA7 high persister mutant survived better in the murine model when competed directly with the wild type. These three avenues of research serve to broaden our understanding of persisters and their mechanism of formation. Understanding the underlying mechanism of persister formation, as well as the clinical implication of persisters can help us better eradicate these cells. Ultimately, determining how persisters form will guide patient treatment in the future. In knowing this relationship, researchers may be able to find target genes for future anti-persister antibiotics, thus abolishing their role in chronic infection. --Author's abstract