{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T04:26:34Z","timestamp":1790655994842,"version":"4.1.0"},"reference-count":19,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2022,2,18]],"date-time":"2022-02-18T00:00:00Z","timestamp":1645142400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001825","name":"Danish Agency for Science and Higher Education","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100001825","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Microbiol."],"abstract":"<jats:sec><jats:title>Introduction<\/jats:title><jats:p>Extended-spectrum beta-lactamase (ESBL) producing <jats:italic>Escherichia coli<\/jats:italic> have become prevalent worldwide, with <jats:italic>E. coli<\/jats:italic> of sequence type 131 (ST131) as the dominant genotype. <jats:italic>E. coli<\/jats:italic> ST131 predominantly exhibits the serotype O25, is associated with the ESBL CTX-M-15 and belongs to a well-defined subclade within the Fim<jats:italic>H<\/jats:italic>30-R clade, Fim<jats:italic>H<\/jats:italic>30-Rx\/C2. Multidrug resistance may have fitness costs for the bacteria. The aim of the current study was to investigate the fitness burden compared to a susceptible ST131 isolate without resistance genes <jats:italic>in vitro<\/jats:italic> and <jats:italic>in vivo<\/jats:italic> and describe genetic differences between fit and less fit isolates.<\/jats:p><\/jats:sec><jats:sec><jats:title>Materials and methods<\/jats:title><jats:p>From a collection of clinical ESBL and non-ESBL <jats:italic>E. coli<\/jats:italic> isolates from urinary tract infection, we selected 16 <jats:italic>bla<\/jats:italic><jats:sub>CTX\u2013M\u201315<\/jats:sub>-positive isolates of ST131. The <jats:italic>in vitro<\/jats:italic> fitness was examined, and relative bacterial fitness (fit<jats:sub><jats:italic>t<\/jats:italic><\/jats:sub>) was determined by direct competition with a fully susceptible ST131 isolate and illustrated in percent, with &amp;lt;100% resulting in a lower fitness, compared to the susceptible reference isolate. The isolates were subjected to whole-genome sequencing and analyzed for resistance markers, plasmids, phage content, and serotype. <jats:italic>In vivo<\/jats:italic> competition was tested in a mouse colonization model.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>The majority (12 out of 16) of the CTX-M-15-producing isolates had a slightly lower relative fitness compared to the susceptible ST131 isolate (mean, 97.6%; range, 82.6\u2013108%) <jats:italic>in vitro<\/jats:italic>. Three isolates had a better fitness than the susceptible ST131 isolate, and one isolate had an identical fitness to the susceptible ST131 isolate. The <jats:italic>in vitro<\/jats:italic> fitness showed no correlation to the number of plasmids, number of phages, number of resistances, or genome size. For the <jats:italic>in vivo<\/jats:italic> competition assays, all three ESBL-producing isolates showed better colonization of the ESBL-resistant ST131 isolates compared to the susceptible ST131 isolate.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>This study shows that ESBL-producing ST131\/<jats:italic>H<\/jats:italic>30-Rx are not necessarily burdened by multidrug resistance, however, have a better <jats:italic>in vitro<\/jats:italic> fitness than the susceptible isolate. These data contribute to the understanding of the success of ST131\/<jats:italic>H<\/jats:italic>30-Rx, although they do not indicate ways to overcome this highly fit, virulent, and antimicrobial-resistant clone.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fmicb.2021.798473","type":"journal-article","created":{"date-parts":[[2022,2,18]],"date-time":"2022-02-18T06:44:30Z","timestamp":1645166670000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":8,"title":["In vitro Relative Fitness, in vivo Intestinal Colonization and Genomic Differences of Escherichia coli of ST131 Carrying blaCTX\u2013M\u201315"],"prefix":"10.3389","volume":"12","author":[{"given":"Frederik Bo\u00ebtius","family":"Hertz","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rasmus L.","family":"Marvig","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Niels","family":"Frimodt-M\u00f8ller","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karen Leth","family":"Nielsen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2022,2,18]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"1","DOI":"10.1101\/039123","article-title":"Sequential acquisition of virulence and fluoroquinolone resistance has shaped the evolution of Escherichia coli ST131.","volume":"7","author":"Ben Zakour","year":"2016","journal-title":"MBio"},{"key":"B2","doi-asserted-by":"publisher","first-page":"1164","DOI":"10.1128\/IAI.01376-12","article-title":"Role of enteroaggregative Escherichia coli virulence factors in uropathogenesis.","volume":"81","author":"Boll","year":"2013","journal-title":"Infect. 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