P-1212. Effects of Quorum Sensing–Interfering Agents, Including Macrolides and Furanone C-30, and an Efflux Pump Inhibitor on Nitrosative Stress Sensitivity in Pseudomonas aeruginosa

Background Long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infection, despite the limited clinically achievable concentrations far below their MICs. An increase in the sub-MIC of macrolide exposure-dependent sensitivity to nitrosative stress is a typical characteristic of P. aeruginosa. However, a few P. aeruginosa clinical isolates do not respond to sub-MIC of macrolide treatment. Therefore, we examined the effects of sub-MIC of macrolide on the sensitivity to nitrosative stress together with an efflux pump inhibitor (EPI). In addition, due to macrolides interfering with quorum sensing (QS), we confirmed the effect of QS-interfering agents furanone C-30 (C-30).Efflux of erythromycin and furanone C-30 by efflux pumps and the effect of efflux pump inhibitor PAβN Methods Nitric oxide (NO) sensitivity assays were performed using P. aeruginosa PAO1, efflux pump-mutant strains, and 11 clinical isolates. Strains were reacted with erythromycin (EM) 10 µg/mL as macrolide, C-30 10 µM as QS inhibitor, phenylalanine arginyl β-naphthylamide (PAβN) 10 µg/mL as EPI, and DETA NONOate 100 µM as NO donor, respectively. The number of viable bacteria was determined using bacterial plate count. Results The sensitivity to nitrosative stress increased when using EPI in treatment with sub-MIC of macrolide, suggesting that the efflux pump was involved in inhibiting the sub-MIC of macrolide effect (at least n=3, p< 0.01). Analysis using efflux pump-mutant P. aeruginosa revealed that MexAB-OprM, MexXY-OprM, and MexCD-OprJ are factors in reducing the sub-MIC of macrolide effect (at least n=3, p< 0.01). We also demonstrated that the QS-interfering agent C-30 producing greater sensitivity to NO stress than EM, and the effect of C-30 was decreased by overproduction of MexAB-OprM. To investigate whether the increase in the QS-interfering agent exposure-dependent sensitivity to nitrosative stress is characteristic of P. aeruginosa clinical isolates, we examined the viability of P. aeruginosa treated with NO. As a result, in 9 of 11 strains, C-30 was highly effective at reducing cell viability, and treatment with both C-30 and PAβN was sufficiently effective against the remaining isolates. Conclusion The combination of a QS-interfering agent and an EPI could be effective in treating P. aeruginosa infections. Disclosures All Authors: No reported disclosures