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

Background: Trans-translation mediated by SsrA (tmRNA) and its associated protein SmpB plays an important role in rescuing stalled ribosomes and detoxifying toxic protein products under stress conditions. However, the role of SsrAandSmpBin bacterial persister survival has not beenstudied.The recent finding that pyrazinamide asaunique persister drug inhibits trans-translation in Mycobacterium tuberculosis prompted us to examine the role of transtranslation in persister survival. Methods: Using Escherichia coli as a model, we constructed SsrA and SmpB mutants and assessed the susceptibility of the mutants to various antibiotics and stress conditions in MIC/MBC and persister assays. Results:We found thatmutations in SsrAand SmpB caused a defect in persister survival as shown by 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 SmpB mutant wasmore susceptible to antibiotics and stresses than the SsrAmutant. A particularly interesting finding is the hypersusceptibility of the SmpB mutant and the SsrA mutant to trimethoprim. The defect of various SsrA and SmpB mutant phenotypes could be complemented by functional ssrA and smpB, respectively. Conclusions:We conclude that SsrAand SmpB are important for persister survival andmayserve asa good target for developing new antibiotics that kill persister bacteria for improved treatment of persistent bacterial infections.