en Nervous system (others) Others Experimental research article Experimental research article <p><span style="line-height:1.6;"><span style="font-size:12px;"><span style="font-family:Arial;"><strong>Introduction:</strong> The high-level antimicrobial resistance, particularly carbapenem resistance, in Pseudomonas aeruginosa is a global health challenge. The combination of antibiotics and synergy effects is beneficial in control of drug-resistant P. aeruginosa. The synergic interaction of antimicrobial agents is af-fected by the mechanisms of antimicrobial resistance. The aim of the current study was to evaluate the effect of efflux pump inhibition on the synergy of antibiotics against carbapenem-resistant P. aeruginosa.<br /> <strong>Methods: </strong>The antibiotics&rsquo; minimum inhibitory concentration (MIC) was determined by the microbroth dilu-tion method. The synergy effect of antibiotics was determined using the checkerboard assay with-out and with Resistance-Nodulation- Division (RND) efflux pump inhibitor phenylalanine-arginine beta-naphthylamide (PA&beta;N).<br /> <strong>Results:</strong> The highest levels of synergistic effects were found between cefepime/tobramycin and meropenem/tobramycin combinations in 35.3% of isolates. After adding PA&beta;N, the most frequent synergistic effects were observed between the meropenem/ciprofloxacin and cefepime/ciprofloxacin combinations, found in 64.7% of isolates. The adding PA&beta;N led to an increase in the synergy of all combinations except tobramycin/colistin. The highest effect of PA&beta;N on the synergy effects of antibiotics combination was observed in meropenem/ciprofloxacin, cefepime/ciprofloxacin, and ciprofloxacin/colistin (an increase of 41.2%).&nbsp;<br /> <strong>Conclusion:</strong> RND efflux pump inhibition has a noticeable effect on the results of synergy tests of some antimi-crobial agent combinations. Given the drug- and strain-dependent effects of PA&beta;N on synergy re-sults, the effects of efflux pump inhibitors should be studied on different combinations of drugs and a large population of bacterial strains.&nbsp;</span></span></span></p> Synergy, Efflux pumps, inhibitors, Pseudomonas aeruginosa 314 323 http://ppj.phypha.ir/browse.php?a_code=A-10-971-3&slc_lang=en&sid=1 Mahsa Vahdatipur Dizaj vahdati_elect90@yahoo.com 3200319475328460036196 0009000083769816 No Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Reza Ghotaslou rzgottaslo@yahoo.com 3200319475328460036197 0000000347623558 No Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Mina Yekani mina_yekani71@yahoo.com 3200319475328460036198 0000000289913521 No Department of Microbiology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran Seyyed Reza Moaddab srmoaddab@gmail.com 3200319475328460036199 0000000158452307 No Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Behrooz Naghili naghili_b@yahoo.com 3200319475328460036200 0000000162497751 No Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Edris Nabizadeh nabizadeh.edris@gmail.com 3200319475328460036201 0000000281928382 No Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Mohammad Yousef Memar y.memar@yahoo.com 3200319475328460036202 0000000203284753 Yes Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran