{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T21:07:55Z","timestamp":1792789675686,"version":"4.5.0"},"reference-count":39,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,16]],"date-time":"2026-09-16T00:00:00Z","timestamp":1789516800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Victor Babes University of Medicine and Pharmacy Timisoara","id":[{"id":"https:\/\/ror.org\/00afdp487","id-type":"ROR","asserted-by":"crossref"}]},{"id":[{"id":"https:\/\/ror.org\/00afdp487","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Microorganisms"],"abstract":"<jats:p>Extensively drug-resistant (XDR) Gram-negative bacilli increasingly exhaust therapeutic options, leaving colistin and cefiderocol as last-resort agents. We assessed whether cefiderocol retains in vitro activity against colistin-resistant isolates, without inferring clinical efficacy. We analysed 236 non-duplicate XDR Gram-negative isolates from 220 patients. Cefiderocol and colistin MICs were determined via reference broth microdilution with EUCAST-required quality control (iron-depleted broth for cefiderocol; mcr-1-positive Escherichia coli NCTC 13846 for colistin) and interpreted using species-specific EUCAST v16.1 (2026) breakpoints (cefiderocol: Enterobacterales S \u2264 2, I 4, R &gt; 4 mg\/L; Pseudomonas aeruginosa S \u2264 2, R &gt; 2 mg\/L; colistin: P. aeruginosa S \u2264 4 mg\/L). Because EUCAST publishes no clinical cefiderocol breakpoint for Acinetobacter baumannii, the primary analysis comprised species with breakpoints for both agents (n = 150; 126 paired); A. baumannii is reported as an MIC distribution and the pooled 236-isolate comparison as secondary. In the primary analysis, 120\/150 isolates (80.0%) were cefiderocol-susceptible at standard or increased exposure. Among paired isolates, cefiderocol covered 77.0% versus 43.7% for colistin; agreement was negligible (Cohen\u2019s \u03ba = 0.020), with 54 isolates favouring cefiderocol and 12 the reverse (McNemar p &lt; 0.001). Conditional in vitro susceptibility among 71 colistin-resistant isolates was 76.1% (95% CI 65.0\u201384.5), giving 33.3 percentage points of incremental coverage and one additional cefiderocol-susceptible isolate per 2.3 matched isolates tested. Secondary analyses were directionally consistent (incremental coverage 21.8\u201333.3 points). These in vitro findings support paired testing of both agents to identify isolates retaining cefiderocol activity when colistin does not; clinical benefit was not assessed.<\/jats:p>","DOI":"10.3390\/microorganisms14092071","type":"journal-article","created":{"date-parts":[[2026,9,16]],"date-time":"2026-09-16T16:07:29Z","timestamp":1789574849000},"page":"2071","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Paired In Vitro Susceptibility of Cefiderocol and Colistin in Colistin-Resistant, Extensively Drug-Resistant Gram-Negative Bacilli: A Single-Centre, MIC-Based Analysis of 236 Clinical Isolates"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-8805-2046","authenticated-orcid":false,"given":"Elena","family":"Hogea","sequence":"first","affiliation":[{"name":"Discipline of Microbiology, Victor Babes University of Medicine and Pharmacy, 300041 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-9681-8289","authenticated-orcid":false,"given":"Nicolae Ciprian","family":"Pilut","sequence":"additional","affiliation":[{"name":"Department of Dermatology, Victor Babes University of Medicine and Pharmacy Timisoara, Eftimie Murgu Square 2, 300041 Timisoara, Romania"},{"name":"Center for the Morphologic Study of the Skin (MORPHODERM), Victor Babes University of Medicine and Pharmacy Timisoara, 300041 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4711-4315","authenticated-orcid":false,"given":"Felix","family":"Bratosin","sequence":"additional","affiliation":[{"name":"Discipline of Infectious Diseases, Victor Babes University of Medicine and Pharmacy, 300041 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andra-Nicole","family":"Rusnac","sequence":"additional","affiliation":[{"name":"Microbiology Laboratory, \u201cPius Brinzeu\u201d County Clinical Emergency Hospital, 300723 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Oana","family":"Plavitu","sequence":"additional","affiliation":[{"name":"Clinical Hospital of Infectious Diseases and Pulmonology \u201cDr. Victor Babes\u201d, 300310 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Livia","family":"Stanga","sequence":"additional","affiliation":[{"name":"Discipline of Microbiology, Victor Babes University of Medicine and Pharmacy, 300041 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7896-1253","authenticated-orcid":false,"given":"Horia Silviu","family":"Branea","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine I\u2014Medical Semiotics II, Victor Babes University of Medicine and Pharmacy, 300041 Timisoara, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"318","DOI":"10.1016\/S1473-3099(17)30753-3","article-title":"Discovery, research, and development of new antibiotics: The WHO priority list of antibiotic-resistant bacteria and tuberculosis","volume":"18","author":"Tacconelli","year":"2018","journal-title":"Lancet Infect. 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