trans-translation mediates tolerance to multiple antibiotics and stresses in Escherichia coli

Background: Trans-translationmediated bySsrA (tmRNA) and its associated protein SmpBplays an important role in rescuing stalled ribosomes and detoxifying toxic protein products under stress conditions. However, the role of SsrAandSmpB inbacterial persister survivalhasnotbeenstudied.The recentfinding thatpyrazinamideasaunique persister drug inhibits trans-translation in Mycobacterium tuberculosis prompted us to examine the role of trans-translation in persister survival. Methods: Using Escherichia coli as a model, we constructed SsrA and SmpB mutants and assessed the suscepti-bility of the mutants to various antibiotics and stress conditions in MIC/MBC and persister assays. Results:Wefound thatmutations in SsrAandSmpB causedadefect inpersister survival as shownby their increased susceptibility to a variety of antibiotics, including gentamicin, streptomycin, amikacin, norfloxacin, trimethoprim and tetracycline, and also stresses, such as acid, weak acid salicylate, heat and peroxide. Additionally, the SsrA and SmpB mutants were 2–8-fold more susceptible than the parent strain to various antibiotics in MIC and MBC tests. The SmpBmutant wasmore susceptible to antibiotics and stresses than the SsrAmutant. A particularly interesting finding is the hypersusceptibility of the SmpBmutant and the SsrA mutant to trimethoprim. The defect of various SsrA and SmpBmutant phenotypes could be complemented by functional ssrA and smpB, respectively. Conclusions:Weconclude that SsrAandSmpBare important for persister survival andmayserveasagood target fo