{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T09:19:05Z","timestamp":1787649545454,"version":"build-2736575974"},"reference-count":40,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T00:00:00Z","timestamp":1787616000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100018818","name":"National Research Development and Innovation Office","doi-asserted-by":"publisher","award":["NKFIH PD 147156"],"award-info":[{"award-number":["NKFIH PD 147156"]}],"id":[{"id":"10.13039\/501100018818","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100018818","name":"National Research Development and Innovation Office","doi-asserted-by":"publisher","award":["2021-1.2.6-T\u00c9T-IPARI-MA-2022-00015"],"award-info":[{"award-number":["2021-1.2.6-T\u00c9T-IPARI-MA-2022-00015"]}],"id":[{"id":"10.13039\/501100018818","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100018818","name":"National Research Development and Innovation Office","doi-asserted-by":"publisher","award":["EK\u00d6P-26-3-II-PTE-993"],"award-info":[{"award-number":["EK\u00d6P-26-3-II-PTE-993"]}],"id":[{"id":"10.13039\/501100018818","id-type":"DOI","asserted-by":"publisher"}]},{"award":["NKFIH PD 147156"],"award-info":[{"award-number":["NKFIH PD 147156"]}],"id":[{"id":"https:\/\/ror.org\/03g2am276","id-type":"ROR","asserted-by":"publisher"}]},{"award":["2021-1.2.6-T\u00c9T-IPARI-MA-2022-00015"],"award-info":[{"award-number":["2021-1.2.6-T\u00c9T-IPARI-MA-2022-00015"]}],"id":[{"id":"https:\/\/ror.org\/03g2am276","id-type":"ROR","asserted-by":"publisher"}]},{"award":["EK\u00d6P-26-3-II-PTE-993"],"award-info":[{"award-number":["EK\u00d6P-26-3-II-PTE-993"]}],"id":[{"id":"https:\/\/ror.org\/03g2am276","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Plants"],"abstract":"<jats:p>The increasing prevalence of multidrug-resistant (MDR) Gram-negative bacteria has stimulated the search for plant-derived antimicrobials with alternative modes of action. This study investigated whether chemically distinct essential oils (EOs) differ in their antibacterial effects and their ability to modulate bacterial efflux-associated processes in clinically relevant MDR pathogens. The chemical compositions of tea tree (Melaleuca alternifolia), lemon (Citrus limon), Scots pine (Pinus sylvestris), and Eucalyptus radiata EOs, as well as their blend, were characterized by gas chromatography\u2013mass spectrometry (GC-MS). Terpinen-4-ol, limonene, \u03b1-pinene, and eucalyptol were identified as major constituents. Antibacterial activity against Escherichia coli and Klebsiella pneumoniae strains with different resistance profiles was evaluated by broth microdilution, while effects on efflux-associated processes were assessed using an ethidium bromide accumulation assay. The EOs showed strain-dependent antibacterial effects, with E. coli being more susceptible than K. pneumoniae. E. radiata showed the lowest MIC against E. coli 130063 (0.312 mg\/mL), whereas no EO inhibited the K. pneumoniae strains at concentrations below 5 mg\/mL. The highest RFI values were observed for lemon oil against K. pneumoniae 33443 (1.41) and the EO blend against E. coli 128673 (1.27). These findings support further investigation of selected EOs as complementary antimicrobial agents.<\/jats:p>","DOI":"10.3390\/plants15172587","type":"journal-article","created":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T08:00:48Z","timestamp":1787644848000},"page":"2587","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Selected Essential Oils Modulate Ethidium Bromide Accumulation and Exhibit Antibacterial Activity Against Multidrug-Resistant Escherichia coli and Klebsiella pneumoniae"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-1989-116X","authenticated-orcid":false,"given":"Edit","family":"Ormai","sequence":"first","affiliation":[{"name":"Department of Pharmacognosy, Faculty of Pharmacy, University of P\u00e9cs, 7624 P\u00e9cs, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8638-5815","authenticated-orcid":false,"given":"Nikoletta","family":"Szemer\u00e9di","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology Educational and Research Center, Albert Szent-Gy\u00f6rgyi Medical School, University of Szeged, 6725 Szeged, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B\u00e9la","family":"Kocsis","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology and Immunology, Medical School, University of P\u00e9cs, 7624 P\u00e9cs, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5166-7871","authenticated-orcid":false,"given":"Margita","family":"Szil\u00e1gyi-Utcz\u00e1s","sequence":"additional","affiliation":[{"name":"Center for Sports Nutrition Science, Hungarian University of Sports Science, 1123 Budapest, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tam\u00e1s","family":"Ollmann","sequence":"additional","affiliation":[{"name":"Department of Physiology, Medical School, University of P\u00e9cs, 7622 P\u00e9cs, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8085-0950","authenticated-orcid":false,"given":"Gabriella","family":"Spengler","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology Educational and Research Center, Albert Szent-Gy\u00f6rgyi Medical School, University of Szeged, 6725 Szeged, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5344-0294","authenticated-orcid":false,"given":"Gy\u00f6rgyi","family":"Horv\u00e1th","sequence":"additional","affiliation":[{"name":"Department of Pharmacognosy, Faculty of Pharmacy, University of P\u00e9cs, 7624 P\u00e9cs, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vikt\u00f3ria Lilla","family":"Bal\u00e1zs","sequence":"additional","affiliation":[{"name":"Department of Pharmacognosy, Faculty of Pharmacy, University of P\u00e9cs, 7624 P\u00e9cs, Hungary"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"598","DOI":"10.1016\/j.mpaic.2015.09.010","article-title":"Nosocomial infections in the intensive care unit","volume":"16","author":"Trubiano","year":"2015","journal-title":"Anaesth. 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