{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T17:02:55Z","timestamp":1790096575381,"version":"4.0.1"},"reference-count":33,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,20]],"date-time":"2026-09-20T00:00:00Z","timestamp":1789862400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Antibiotics"],"abstract":"<jats:p>Objectives: The fourth-generation fluoroquinolone delafloxacin (DFX) is propagated as a novel (oral) treatment option for infections with multidrug-resistant Gram-negatives. To date, efficacy data for Enterobacterales is only available for wild-type isolates but not for those with pre-existing resistance against third-generation fluoroquinolones. Methods: One hundred twenty-nine non-duplicate clinical isolates of Enterobacterales that demonstrated ciprofloxacin resistance in VITEK 2 testing were collected and analyzed for CIP and DFX minimum inhibitory concentrations (MICs) via broth microdilution. Results: DFX MICs ranged from 0.5 to \u2265 16 mg L\u22121 (median: 4 mg L\u22121). All Escherichia coli isolates (n = 56; 43% of all isolates), the only species with EUCAST breakpoints, were classified as DFX resistant. All other isolates belonging to species for which EUCAST epidemiological cut-offs (ECOFFs) are available (n = 64; 50% of all isolates) demonstrated MICs above the ECOFF. With a minimum and median MIC of 2 and 8 mg L\u22121, respectively, the remaining isolates (6%) achieved similar results. A moderate correlation between the MIC values of the two fluoroquinolones was found. For the majority of isolates (64%), other oral options for antibiotic therapy, such as amoxicillin\/clavulanic acid and trimethoprim\/sulfamethoxazole, were still available. Conclusions: Our data suggests that, compared to CIP, DFX does not demonstrate increased in vitro efficacy against fluoroquinolone-resistant Enterobacterales. Subsequent DFX testing seems to be of limited additional value.<\/jats:p>","DOI":"10.3390\/antibiotics15090934","type":"journal-article","created":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T15:28:43Z","timestamp":1790090923000},"page":"934","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Delafloxacin Resistance and MIC-Distribution in Ciprofloxacin-Resistant Enterobacterales: A Retrospective Evaluation of Minimum Inhibitory Concentrations"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5768-6523","authenticated-orcid":false,"given":"Patrick","family":"Forstner","sequence":"first","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-6947-2487","authenticated-orcid":false,"given":"Isabel","family":"Klugherz","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"}]},{"given":"Hanna","family":"Greimel","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Kathrin","family":"J\u00e4ntsch","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Ute","family":"Wagner-Eibel","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Melanie","family":"Palz","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"given":"Laura","family":"Krieger","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0510-7336","authenticated-orcid":false,"given":"Ivo","family":"Steinmetz","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5032-8870","authenticated-orcid":false,"given":"Karl","family":"Dichtl","sequence":"additional","affiliation":[{"name":"Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, 8010 Graz, Austria"},{"name":"Institute of Laboratory Medicine and Microbiology, Protestant Hospital of Bethel Foundation, Campus Bielefeld-Bethel, University Hospital OWL of Bielefeld University, 33617 Bielefeld, Germany"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Geremia, N., Giovagnorio, F., Colpani, A., De Vito, A., Botan, A., Stroffolini, G., Toc, D.A., Zerbato, V., Principe, L., and Madeddu, G. (2024). Fluoroquinolones and Biofilm: A Narrative Review. Pharmaceuticals, 17.","DOI":"10.3390\/ph17121673"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Rodrigues, C.F., and Silva, F. (2025). The Rise, Fall, and Rethink of (Fluoro) Quinolones: A Quick Rundown. Pathogens, 14.","DOI":"10.3390\/pathogens14060525"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"5829","DOI":"10.1038\/s41467-025-60688-3","article-title":"Structural Basis of Topoisomerase Targeting by Delafloxacin","volume":"16","author":"Najmudin","year":"2025","journal-title":"Nat. Commun."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"S113","DOI":"10.1086\/428051","article-title":"The Quinolones: Past, Present, and Future","volume":"41","author":"Andriole","year":"2005","journal-title":"Clin. Infect. Dis."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"793","DOI":"10.1016\/j.mcna.2011.03.006","article-title":"The Newer Fluoroquinolones","volume":"95","author":"Bolon","year":"2011","journal-title":"Med. Clin. N. Am."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"116518","DOI":"10.1016\/j.diagmicrobio.2024.116518","article-title":"Delafloxacin, an Alternative Treatment for Levofloxacin-Resistant Staphylococci in Osteoarticular Infections: To Use or Not to Use?","volume":"110","author":"Loiez","year":"2024","journal-title":"Diagn. Microbiol. Infect. Dis."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Bolanos, S., Acebes, C., Martinez-Exposito, O., Boga, J.A., Fernandez, J., and Rodriguez-Lucas, C. (2024). Role of ParC Mutations at Position 84 on High-Level Delafloxacin Resistance in Methicillin-Resistant Staphylococcus Aureus. Antibiotics, 13.","DOI":"10.3390\/antibiotics13070641"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"279","DOI":"10.1097\/OLQ.0000000000000971","article-title":"Efficacy and Safety of Single-Dose Oral Delafloxacin Compared With Intramuscular Ceftriaxone for Uncomplicated Gonorrhea Treatment: An Open-Label, Noninferiority, Phase 3, Multicenter, Randomized Study","volume":"46","author":"Hook","year":"2019","journal-title":"Sex. Transm. Dis."},{"key":"ref_9","unstructured":"World Health Organization (2019). World Health Organization Critically Important Antimicrobials for Human Medicine 2019."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"649","DOI":"10.1128\/AAC.01201-10","article-title":"Contrasting Effects of Acidic PH on the Extracellular and Intracellular Activities of the Anti-Gram-Positive Fluoroquinolones Moxifloxacin and Delafloxacin against Staphylococcus Aureus","volume":"55","author":"Lemaire","year":"2011","journal-title":"Antimicrob. Agents Chemother."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"e0270521","DOI":"10.1128\/spectrum.02705-21","article-title":"Activity of Delafloxacin and Levofloxacin against Stenotrophomonas Maltophilia at Simulated Plasma and Intrapulmonary PH Values","volume":"10","author":"Vialichka","year":"2022","journal-title":"Microbiol. Spectr."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"2605","DOI":"10.1093\/jac\/dkaa209","article-title":"Delafloxacin Activity against Staphylococcus Aureus with Reduced Susceptibility or Resistance to Methicillin, Vancomycin, Daptomycin or Linezolid","volume":"75","author":"Saravolatz","year":"2020","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"dlad034","DOI":"10.1093\/jacamr\/dlad034","article-title":"The in Vitro Activity of Delafloxacin and Comparator Agents against Bacterial Pathogens Isolated from Patients with Cancer","volume":"5","author":"Gerges","year":"2023","journal-title":"JAC Antimicrob. Resist."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"278","DOI":"10.1016\/j.jgar.2020.09.027","article-title":"Update on the Activity of Delafloxacin against Acute Bacterial Skin and Skin-Structure Infection Isolates from European Hospitals (2014\u20132019)","volume":"23","author":"Shortridge","year":"2020","journal-title":"J. Glob. Antimicrob. Resist."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"e001002","DOI":"10.1136\/bmjophth-2022-001002","article-title":"Potential New Fluoroquinolone Treatments for Suspected Bacterial Keratitis","volume":"7","author":"Herbert","year":"2022","journal-title":"BMJ Open Ophthalmol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"e0009922","DOI":"10.1128\/spectrum.00099-22","article-title":"In Vitro Activity of Delafloxacin and Finafloxacin against Mycoplasma Hominis and Ureaplasma Species","volume":"10","author":"Kong","year":"2022","journal-title":"Microbiol. Spectr."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"211","DOI":"10.1089\/mdr.2025.0046","article-title":"In Vitro Activity of Novel Antibiotics Against Corynebacterium Spp. Clinical Isolates Responsible for Difficult-to-Treat Infections","volume":"31","author":"Bichali","year":"2025","journal-title":"Microb. Drug Resist."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"e02609-16","DOI":"10.1128\/AAC.02609-16","article-title":"In Vitro Activity of Delafloxacin against Contemporary Bacterial Pathogens from the United States and Europe, 2014","volume":"61","author":"Pfaller","year":"2017","journal-title":"Antimicrob. Agents Chemother."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2771","DOI":"10.1128\/AAC.48.7.2771-2777.2004","article-title":"In Vitro and Bactericidal Activities of ABT-492, a Novel Fluoroquinolone, against Gram-Positive and Gram-Negative Organisms","volume":"48","author":"Almer","year":"2004","journal-title":"Antimicrob. Agents Chemother."},{"key":"ref_20","unstructured":"World Health Organization (2024). WHO Bacterial Priority Pathogens List 2024: Bacterial Pathogens of Public Health Importance, to Guide Research, Development, and Strategies to Prevent and Control Antimicrobial Resistance."},{"key":"ref_21","unstructured":"The European Committee on Antimicrobial Susceptibility Testing (2026, August 18). MIC and Zone Diameter Distributions\u2014MIC Distributions for Delafloxacin. Available online: https:\/\/mic.eucast.org."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1439","DOI":"10.1093\/jac\/dkx543","article-title":"Clinical Review of Delafloxacin: A Novel Anionic Fluoroquinolone","volume":"73","author":"Mogle","year":"2018","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"105064","DOI":"10.1016\/j.idnow.2025.105064","article-title":"The Safety Profile of Fluoroquinolones","volume":"55","author":"Largeau","year":"2025","journal-title":"Infect. Dis. Now"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1016\/j.eimc.2020.09.016","article-title":"In Vitro Activity of Delafloxacin against Highly Levofloxacin-Resistant Invasive Isolates of Streptococcus Pneumoniae","volume":"40","author":"Cercenado","year":"2022","journal-title":"Enferm. Infecc. Microbiol. Clin. (Engl. Ed.)"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"405","DOI":"10.1016\/j.cmi.2023.12.008","article-title":"In Vitro Susceptibility to Delafloxacin of Pseudomonas Aeruginosa with Resistance to Other Quinolones (Ciprofloxacin and Levofloxacin)","volume":"30","author":"Santotoribio","year":"2024","journal-title":"Clin. Microbiol. Infect."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"116","DOI":"10.1111\/crj.13262","article-title":"Delafloxacin\u2014A Novel Fluoroquinolone for the Treatment of Ciprofloxacin-Resistant Pseudomonas Aeruginosa in Patients with Cystic Fibrosis","volume":"15","author":"Millar","year":"2021","journal-title":"Clin. Respir. J."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"e01603-19","DOI":"10.1128\/JCM.01603-19","article-title":"Activity of Potential Alternative Treatment Agents for Stenotrophomonas Maltophilia Isolates Nonsusceptible to Levofloxacin and\/or Trimethoprim-Sulfamethoxazole","volume":"58","author":"Biagi","year":"2020","journal-title":"J. Clin. Microbiol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1080\/17512433.2022.2100346","article-title":"A Profile of Delafloxacin in the Treatment of Adults with Community-Acquired Bacterial Pneumonia","volume":"15","author":"Sendra","year":"2022","journal-title":"Expert Rev. Clin. Pharmacol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"103867","DOI":"10.1016\/j.bjid.2024.103867","article-title":"Comparative in Vitro Activity of Delafloxacin and Other Antimicrobials against Isolates from Patients with Acute Bacterial Skin, Skin-Structure Infection and Osteomyelitis","volume":"28","author":"Ribeiro","year":"2024","journal-title":"Braz. J. Infect. Dis."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Gulyas, D., Kamotsay, K., Szabo, D., and Kocsis, B. (2023). Investigation of Delafloxacin Resistance in Multidrug-Resistant Escherichia Coli Strains and the Detection of E. Coli ST43 International High-Risk Clone. Microorganisms, 11.","DOI":"10.3390\/microorganisms11061602"},{"key":"ref_31","unstructured":"The European Committee on Antimicrobial Susceptibility Testing (2022). Media Preparation for EUCAST Disk Diffusion Testing and for Determination of MIC Values by the Broth Microdilution Method V7.0, The European Committee on Antimicrobial Susceptibility Testing."},{"key":"ref_32","unstructured":"(2019). Susceptibility Testing of Infectious Agents and Evaluation of Performance of Antimicrobial Susceptibility Test Devices Part 1: Broth Micro-Dilution Reference Method for Testing the in Vitro Activity of Antimicrobial Agents against Rapidly Growing Aerobic Bacteria Involved in Infectious Diseases (Standard No. ISO 20776-1)."},{"key":"ref_33","unstructured":"The European Committee on Antimicrobial Susceptibility Testing (2025). Breakpoint Tables for Interpretation of MICs and Zone Diameters, Version 15.0, The European Committee on Antimicrobial Susceptibility Testing."}],"container-title":["Antibiotics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2079-6382\/15\/9\/934\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T16:02:36Z","timestamp":1790092956000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2079-6382\/15\/9\/934"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,20]]},"references-count":33,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["antibiotics15090934"],"URL":"https:\/\/doi.org\/10.3390\/antibiotics15090934","relation":{},"ISSN":["2079-6382"],"issn-type":[{"value":"2079-6382","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,20]]}}}