{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:56:39Z","timestamp":1787028999086,"version":"build-2736575974"},"reference-count":49,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2025,4,7]],"date-time":"2025-04-07T00:00:00Z","timestamp":1743984000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Medical University of Varna, Bulgaria","award":["21012"],"award-info":[{"award-number":["21012"]}]},{"name":"Medical University of Varna, Bulgaria","award":["2412098"],"award-info":[{"award-number":["2412098"]}]},{"name":"Bulgarian Current Research Information System (NACID)","award":["21012"],"award-info":[{"award-number":["21012"]}]},{"name":"Bulgarian Current Research Information System (NACID)","award":["2412098"],"award-info":[{"award-number":["2412098"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Microorganisms"],"abstract":"<jats:p>Antimicrobial resistance (AMR) poses a global health threat, with multidrug-resistant (MDR) Klebsiella pneumoniae and Pseudomonas aeruginosa contributing to the burden, especially in Bulgaria. This study investigates recent resistance trends of these pathogens in Bulgaria and evaluates the antibacterial effects of commercially available oregano (Origanum vulgare) and thyme (Thymus vulgaris) essential oils (EOs), both alone and in combination with conventional antibiotics. The chemical composition of the EOs was analyzed using gas chromatography\u2013mass spectrometry (GC-MS), revealing carvacrol (84.2%) as the main component in oregano EO and thymol (45.74%) in thyme EO. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the EOs were determined using the serial dilution method. Oregano EO exhibited lower MIC and MBC values (0.039\u20131.250%) compared to thyme EO (0.156\u20135.000%) against both pathogens. The disk diffusion assay showed that oregano EO exhibits more potent antibacterial effects than thyme EO in Klebsiella pneumoniae and Pseudomonas aeruginosa strains. The findings highlight the potential of EOs as adjunctive therapies to enhance the efficacy of conventional antibiotics against MDR Klebsiella pneumoniae and Pseudomonas aeruginosa strains in Bulgaria.<\/jats:p>","DOI":"10.3390\/microorganisms13040843","type":"journal-article","created":{"date-parts":[[2025,4,10]],"date-time":"2025-04-10T10:47:41Z","timestamp":1744282061000},"page":"843","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["Antibacterial Effects of Bulgarian Oregano and Thyme Essential Oils Alone and in Combination with Antibiotics Against Klebsiella pneumoniae and Pseudomonas aeruginosa"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7048-3560","authenticated-orcid":false,"given":"Silviya","family":"Mihaylova","sequence":"first","affiliation":[{"name":"Medical College, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6072-513X","authenticated-orcid":false,"given":"Antoaneta","family":"Tsvetkova","sequence":"additional","affiliation":[{"name":"Medical College, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sylvia","family":"Stamova","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Neli","family":"Ermenlieva","sequence":"additional","affiliation":[{"name":"Department of Microbiology and Virology, Faculty of Medicine, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8146-5050","authenticated-orcid":false,"given":"Gabriela","family":"Tsankova","sequence":"additional","affiliation":[{"name":"Department of Microbiology and Virology, Faculty of Medicine, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2732-6839","authenticated-orcid":false,"given":"Emiliya","family":"Georgieva","sequence":"additional","affiliation":[{"name":"Medical College, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5010-1147","authenticated-orcid":false,"given":"Katya","family":"Peycheva","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Faculty of Pharmacy, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Veselina","family":"Panayotova","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Faculty of Pharmacy, Medical University of Varna, 9002 Varna, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yulian","family":"Voynikov","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Faculty of Pharmacy, Medical University of Sofia, 1000 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,4,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1199","DOI":"10.1016\/S0140-6736(24)01867-1","article-title":"Global burden of bacterial antimicrobial resistance 1990\u20132021: A systematic analysis with forecasts to 2050","volume":"404","author":"Naghavi","year":"2024","journal-title":"Lancet"},{"key":"ref_2","unstructured":"World Health Organization (2024). 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