Glyphosate affects persistence and tolerance but not antibiotic resistance

Abstract

Glyphosate is a herbicide widely used in food production that blocks the synthesis of aromatic amino acids in plants and in microorganisms and also induces the accumulation of the alarmone (p)ppGpp. Resistance, tolerance and persistence to antibiotics are common phenomena that contribute to antibiotic treatment failure. There are several mechanisms through which bacteria attain tolerance or persistence to antibiotics, but all of them involve partial or complete growth inhibition. In this study we evaluated the effect of glyphosate on the resistance, tolerance, and persistence towards the antibiotics ampicillin, ciprofloxacin and kanamycin and the possible role of (p)ppGpp in this activity. Glyphosate did not affect the minimum inhibitory concentration of these antibiotics, but enhanced bacterial tolerance and/or persistence towards them. The upshift in ciprofloxacin and kanamycin tolerance was partially dependent on the presence of relA that promotes (p)ppGpp accumulation in response to glyphosate. Conversely, the strong increase in ampicillin tolerance caused by glyphosate was independent of relA. We conclude that by inducing aromatic amino acid starvation glyphosate contributes to the temporary increase in E. coli tolerance or persistence, but does not affect antibiotic resistance.