Figure 3. Vanillin induces a multi-antibiotic-resistance (mar) phenotype.

a) Vanillin and aspirin (acetylsalicylic acid) have similar drug-drug interaction profiles (see ED Fig. 10), suggesting similar MoA’s. A schematic representation of the mar response induction via deactivation of the MarR repressor by salicylate/aspirin ²¹ is illustrated. b) Vanillin increases AcrA levels in a marA-dependent manner. A representative immunoblot of exponentially growing cells (all blots shown in Supplementary Fig. 1) after treatment with solvent, vanillin (150µg/ml) or aspirin (500µg/ml) is shown - loading controlled by cell density and constitutively expressed RecA. Barplots depict AcrA protein level quantification; c) marA expression levels upon vanillin (150µg/ml) or aspirin (500µg/ml) treatment are stronger in wildtype than in ΔmarR mutant. Expression is measured by RT-qPCR and normalized to no-drug treatment in wildtype; d & e) Vanillin (150 µg/ml) and aspirin (500µg/ml) increase the MIC of chloramphenicol (d) or ciprofloxacin (e). Antagonism is weaker and abolished in ΔmarA and ΔacrA mutants, respectively. n = number of independent biological replicates and error bars depict standard deviation (b-e).