Phenazine-1 carboxylic acid of induces the expression of Tet38 MDR efflux pump and mediates resistance to phenazines and antibiotics.

In this study, we showed that phenazine-1 carboxylic acid (PCA) of induced the expression of Tet38 efflux pump triggering resistance to tetracycline and phenazines. Exposure of RN6390 to supernatants of PA14 and its pyocyanin (PYO)-deficient mutants showed that non-PYO phenazines could induce the expression of Tet38 efflux pump. Direct exposure of RN6390 to PCA compound at 0.25× MIC led to a five-fold increase in transcripts. Expression of Tet38 protein was identified through confocal microscopy using RN6390(pRN-p-) that expressed YFP under control of the promoter by PCA at 0.25× MIC. The MICs of PCA of a Tet38-overexpressor and a mutant showed a three-fold increase and a two-fold decrease, respectively, compared with that of wild-type. Pre-exposure of RN6390 to PCA (0.25× MIC) for 1 hour prior to addition of tetracycline (1× or 10× MIC) improved bacteria viability of 1.5-fold and 2.6-fold, respectively, but addition of NaCl 7% together with tetracycline at 10× MIC reduced the number of viable PCA-exposed RN6390 of a 2.0-log CFU/mL. The transcript levels of , a repressor of , decreased and increased two-fold in the presence of PCA and NaCl, respectively, suggesting that the effects of PCA and NaCl on production occurred through TetR21 expression. These data suggest that PCA-induced Tet38 protects against tetracycline during coinfection with ; however, induced -mediated resistance to tetracycline is reversed by NaCl 7%, a nebulized treatment used to enhance sputum mobilization in CF patients.