{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,23]],"date-time":"2026-09-23T18:30:39Z","timestamp":1790188239405,"version":"4.1.0"},"reference-count":53,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2023,5,12]],"date-time":"2023-05-12T00:00:00Z","timestamp":1683849600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100006013","name":"United Arab Emirates University","doi-asserted-by":"publisher","award":["G00003430"],"award-info":[{"award-number":["G00003430"]}],"id":[{"id":"10.13039\/501100006013","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>The global spread of multidrug-resistant (MDR) bacteria increases the demand for the discovery of new antibiotics and adjuvants. Phenylalanine-arginine \u03b2-naphthylamide (PA\u03b2N) is an inhibitor of efflux pumps in Gram-negative bacteria, such as the AcrAB-TolC complex in Escherichia coli. We aimed to explore the synergistic effect and mechanism of action of PA\u03b2N combined with azithromycin (AZT) on a group of MDR E. coli strains. Antibiotic susceptibility was tested for 56 strains, which were screened for macrolide resistance genes. Then, 29 strains were tested for synergy using the checkerboard assay. PA\u03b2N significantly enhanced AZT activity in a dose-dependent manner in strains expressing the mphA gene and encoding macrolide phosphotransferase, but not in strains carrying the ermB gene and encoding macrolide methylase. Early bacterial killing (6 h) was observed in a colistin-resistant strain with the mcr-1 gene, leading to lipid remodeling, which caused outer membrane (OM) permeability defects. Clear OM damage was revealed by transmission electron microscopy in bacteria exposed to high doses of PA\u03b2N. Increased OM permeability was also proven by fluorometric assays, confirming the action of PA\u03b2N on OM. PA\u03b2N maintained its activity as an efflux pump inhibitor at low doses without permeabilizing OM. A non-significant increase in acrA, acrB, and tolC expression in response to prolonged exposure to PA\u03b2N was noted in cells treated with PA\u03b2N alone or with AZT, as a reflection of bacterial attempts to counteract pump inhibition. Thus, PA\u03b2N was found to be effective in potentiating the antibacterial activity of AZT on E. coli through dose-dependent action. This warrants further investigations of its effect combined with other antibiotics on multiple Gram-negative bacterial species. Synergetic combinations will help in the battle against MDR pathogens, adding new tools to the arsenal of existing medications.<\/jats:p>","DOI":"10.3390\/ijms24108662","type":"journal-article","created":{"date-parts":[[2023,5,12]],"date-time":"2023-05-12T09:56:18Z","timestamp":1683885378000},"page":"8662","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":20,"title":["Boosting the Antibacterial Activity of Azithromycin on Multidrug-Resistant Escherichia coli by Efflux Pump Inhibition Coupled with Outer Membrane Permeabilization Induced by Phenylalanine-Arginine \u03b2-Naphthylamide"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5711-6264","authenticated-orcid":false,"given":"Farah","family":"Al-Marzooq","sequence":"first","affiliation":[{"name":"Department of Medical Microbiology and Immunology, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2552-4807","authenticated-orcid":false,"given":"Akela","family":"Ghazawi","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology and Immunology, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lana","family":"Daoud","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology and Immunology, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Saeed","family":"Tariq","sequence":"additional","affiliation":[{"name":"Department of Anatomy, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,5,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"e24655","DOI":"10.1002\/jcla.24655","article-title":"Antibiotic Resistance: The Challenges and Some Emerging Strategies for Tackling a Global Menace","volume":"36","author":"Ugwu","year":"2022","journal-title":"J. Clin. Lab. Anal."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2225","DOI":"10.1016\/j.drudis.2019.08.004","article-title":"Superbugs but No Drugs: Steps in Averting a Post-Antibiotic Era","volume":"24","author":"Hamad","year":"2019","journal-title":"Drug Discov. 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