Reduced ROS-associated prophage induction in a lepA mutant contributes to increased fluoroquinolone persistence in Salmonella Typhimurium

Bacterial persister cells are known to survive antibiotic treatment in the absence of typical resistance mechanisms. Persisters do not grow in the presence of antibiotics but can resume growth when antibiotic treatment is ceased, persisters are therefore often associated with chronic infections and treatment failure. In previous studies, it was shown that a lepA deletion strain of Escherichia coli was more tolerant to different classes of antibiotics due to reduced formation of reactive oxygen species (ROS). LepA is a highly conserved protein involved in translation, but the details of its role in the various mechanisms it participates in remain unclear. In this study, we performed killing assays to assess persister survival in a lepA deletion strain of Salmonella Typhimurium and FACS analysis to measure ROS formation in response to ciprofloxacin, β-lactam, and aminoglycoside antibiotics, representing three different classes of bactericidal drugs. Our results suggest that deletion of lepA reduces ROS formation and may increase persister survival after ciprofloxacin treatment, possibly due to reduced prophage induction. In contrast, reducing oxidative stress with the antioxidant glutathione was associated with increased persister formation and a larger subpopulation of wild type bacteria lacking prophage induction following ciprofloxacin treatment, whereas no additional beneficial effect was observed in the lepA mutant. These findings are consistent with a link between ROS-associated prophage induction and persister cell levels, providing a cautious perspective on how drug-induced ROS may influence bacterial survival in strains carrying prophages.