Reducing the Periplasmic Glutathione Content Makes Escherichia coli Resistant to Trimethoprim and Other Antimicrobial Drugs.

Although glutathione (GSH) has been shown to influence the antimicrobial effects of many kinds of antibiotics, little is known about its role in relation to trimethoprim (TMP), a widely used antifolate. In this study, several genes related to glutathione metabolism were deleted in different Escherichia coli strains (i.e., O157:H7 and ATCC 25922), and their effects on susceptibility to TMP were tested. The results showed that deleting , , , and caused TMP resistance, and deleting also caused resistance to other drugs. Meanwhile, deleting , , and resulted in a significant decrease of the periplasmic glutathione content. Supplementing exogenous GSH or further deleting glutathione importer genes ( and ) restored TMP sensitivity to Δ. Subsequently, the results of quantitative-reverse transcription PCR experiments showed that expression levels of , , and were significantly upregulated in both Δ and Δ. Correspondingly, deleting led to a decreased accumulation of TMP within bacterial cells, and further deleting , , or restored TMP sensitivity to Δ. Inactivation of CpxR and SoxS, two transcriptional factors that modulate the transcription of -, restored TMP sensitivity to Δ. Furthermore, mutations of , , , , and are highly prevalent in E. coli clinical strains. Collectively, these data suggest that reducing the periplasmic glutathione content of E. coli leads to increased expression of - with the involvement of CpxR and SoxS, ultimately causing drug resistance. To the best of our knowledge, this is the first report showing a linkage between periplasmic GSH and drug resistance in bacteria. After being used extensively for decades, trimethoprim still remains one of the key accessible antimicrobials recommended by the World Health Organization. A better understanding of the mechanisms of resistance would be beneficial for the future utilization of this drug. It has been shown that the AcrAB-TolC efflux pump is associated with trimethoprim resistance in E. coli clinical strains. In this study, we show that E. coli can sense the periplasmic glutathione content with the involvement of the CpxAR two-component system. As a result, reducing the periplasmic glutathione content leads to increased expression of , , and via CpxR and SoxS, causing resistance to antimicrobials, including trimethoprim. Meanwhile, mutations in the genes responsible for periplasmic glutathione content maintenance are highly prevalent in E. coli clinical isolates, indicating a potential correlation of the periplasmic glutathione content and clinical antimicrobial resistance, which merits further investigation.