The study of the acquisition of antibiotic resistance (AR) has mainly focused in inherited processes, namely mutations and acquisition of AR genes. However, inducible, non-inheritable AR has received less attention and most information in this field derives from the study of antibiotics as inducers of their associated resistance mechanisms. Less is known about non-antibiotic compounds or situations that can induce AR during infection. Multidrug resistance efflux pumps are a category of AR

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... inants characterized by the tightly regulation of their expression. Their contribution to acquired AR relies in their overexpression. Herein we analyzed potential inducers of the expression of the chromosomally-encoded Pseudomonas aeruginosa clinically-relevant efflux pumps, MexCD-OprJ and MexAB-OprM. For this purpose, we developed a set of luxCDABE-based P. aeruginosa biosensor strains, which allows the high-throughput analysis of compounds able of modifying the expression of these efflux pumps. Using these strains, we analyzed a set of 240 compounds present in Biolog Phenotype Microarrays. Several inducers of the expression of the genes that encode these efflux pumps were found. The study focused in dequalinium chloride, procaine and atropine, compounds that can be found in clinical settings. Using real-time PCR, we confirmed that these compounds indeed induce the expression of mexCD-oprJ. In addition, P. aeruginosa presents lower susceptibility to ciprofloxacin (a MexCD-OprJ substrate) when dequalinium chloride, procaine or atropine are present. This work emphasizes the need of studying compounds that can trigger transient AR during antibiotic treatment, a phenotype difficult to discover using classical susceptibility tests.