{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T02:44:47Z","timestamp":1785725087017,"version":"3.56.0"},"reference-count":37,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2026,8,1]],"date-time":"2026-08-01T00:00:00Z","timestamp":1785542400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100015811","name":"Natural Science Foundation of Ningxia Hui Autonomous Region","doi-asserted-by":"publisher","award":["2025AAC050040"],"award-info":[{"award-number":["2025AAC050040"]}],"id":[{"id":"10.13039\/100015811","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["32560874"],"award-info":[{"award-number":["32560874"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"award":["32560874"],"award-info":[{"award-number":["32560874"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]},{"name":"College students\u2019 innovative entrepreneurial training plan program","award":["X202610452586"],"award-info":[{"award-number":["X202610452586"]}]},{"name":"industry-academia collaboration projects","award":["HX240393"],"award-info":[{"award-number":["HX240393"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Microorganisms"],"abstract":"<jats:p>The increased occurrence of tetracycline resistance (conferred by the tet(X3)\/tet(X4) resistance genes) poses a major challenge to the clinical treatment of infections using tetracyclines, including tigecycline, which is the \u201clast-resort\u201d therapeutic agent. Thus, there is an urgent need to develop inhibitors targeting Tet(X3)\/Tet(X4) to address the crisis of tetracycline resistance. This study revealed that quercetin is an inhibitor of Tet(X3)\/Tet(X4), which, when combined with different tetracyclines, can exert synergistic growth-inhibitory effects against Tet(X3)\/Tet(X4)-positive bacteria (fractional inhibitory concentration &lt; 0.5). Quercetin + tigecycline significantly decreased the biofilm-forming ability of bacteria. Mechanistic investigations revealed that quercetin inhibits the catalytic activity of Tet(X4) against tetracycline antibiotics by binding to the catalytic active site. In the Galleria mellonella larval infection model of Tet(X4)-positive E. coli J53p47EC or Tet(X4)-negative E. coli J53, tigecycline + quercetin enhanced the survival rate, decreased melanization, and suppressed bacterial load. Thus, the findings of this study will enable the development of novel Tet(X3)\/Tet(X4)-targeted therapeutic strategies for clinical infections caused by drug-resistant Enterobacteriaceae and Acinetobacter baumannii, especially Tet(X3)\/Tet(X4)-positive pathogens.<\/jats:p>","DOI":"10.3390\/microorganisms14081692","type":"journal-article","created":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T01:43:27Z","timestamp":1785721407000},"page":"1692","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The Role of Natural Flavonoid Quercetin in Combating Tet(X3)\/Tet(X4)-Positive Bacterial Infections"],"prefix":"10.3390","volume":"14","author":[{"given":"Xiaokun","family":"Zhan","sequence":"first","affiliation":[{"name":"Institute of Microbe and Host Health, College of Agriculture and Forestry, Linyi University, Linyi 276000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lifeng","family":"Zhou","sequence":"additional","affiliation":[{"name":"Key Laboratory of Ministry of Education for Conservation and Utilization of Special Biological Resources in the Western China, School of Life Sciences, Ningxia University, Yinchuan 750021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hanyu","family":"Wang","sequence":"additional","affiliation":[{"name":"Institute of Microbe and Host Health, College of Agriculture and Forestry, Linyi University, Linyi 276000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lihao","family":"Wang","sequence":"additional","affiliation":[{"name":"Institute of Microbe and Host Health, College of Agriculture and Forestry, Linyi University, Linyi 276000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lizhi","family":"Tian","sequence":"additional","affiliation":[{"name":"Key Laboratory of Ministry of Education for Conservation and Utilization of Special Biological Resources in the Western China, School of Life Sciences, Ningxia University, Yinchuan 750021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7704-187X","authenticated-orcid":false,"given":"Yonglin","family":"Zhou","sequence":"additional","affiliation":[{"name":"Key Laboratory of Ministry of Education for Conservation and Utilization of Special Biological Resources in the Western China, School of Life Sciences, Ningxia University, Yinchuan 750021, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kuan","family":"Gu","sequence":"additional","affiliation":[{"name":"School of Chinese Medicine, Nanjing University of Chinese Medicine, Nanjing 210023, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Houru","family":"Liu","sequence":"additional","affiliation":[{"name":"Institute of Microbe and Host Health, College of Agriculture and Forestry, Linyi University, Linyi 276000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"100947","DOI":"10.1016\/j.lanmic.2024.07.010","article-title":"Antimicrobial resistance: A concise update","volume":"6","author":"Ho","year":"2025","journal-title":"Lancet Microbe"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e082681","DOI":"10.1136\/bmj-2024-082681","article-title":"Antimicrobial use and resistance","volume":"391","author":"Reza","year":"2025","journal-title":"BMJ"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"15559","DOI":"10.3389\/bjbs.2026.15559","article-title":"Antimicrobial Resistance: The Answers","volume":"83","author":"Millar","year":"2026","journal-title":"Br. 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