{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,2]],"date-time":"2026-11-02T01:24:01Z","timestamp":1793582641645,"version":"4.5.0"},"reference-count":94,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2025,12,10]],"date-time":"2025-12-10T00:00:00Z","timestamp":1765324800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100032297","name":"InfectoPharm Arzneimittel und Consilium GmbH","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100032297","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Antibiotics"],"abstract":"<jats:p>Background\/Objectives: Metallo-\u03b2-lactamase (MBL)-producing Gram-negative bacteria represent a growing global health threat due to their broad resistance to \u03b2-lactam antibiotics, including carbapenems, which severely limits treatment options. This study aimed to evaluate the in vitro synergistic activity of fosfomycin (FOS) in combination with selected older and newer antimicrobials against MBL-producing Klebsiella pneumoniae and Pseudomonas aeruginosa. Methods: Synergistic interactions were assessed using agar dilution checkerboard on 42 MBL-producing clinical isolates (22 K. pneumoniae, 20 P. aeruginosa) and confirmed using time-kill assays with selected isolates. FOS was tested in combination with colistin (COL), ceftazidime\u2013avibactam (CAZ-AVI), meropenem (MER), amikacin (AMI), aztreonam (AZT), aztreonam\u2013avibactam (AZT-AVI), or cefiderocol (FDC). Results: Most FOS combinations exhibited additive or synergistic effects against clinical isolates. Synergy rates reached 72.7% for the FOS+CAZ-AVI combination (K. pneumoniae) and 65.0% for the FOS+COL combination (P. aeruginosa). An asymmetric synergistic interaction was identified for FOS+CAZ-AVI, with FOS enhancing the activity of CAZ-AVI more markedly than vice versa, especially in K. pneumoniae. Time-kill assays on selected isolates confirmed synergistic and bactericidal activity of FOS+CAZ-AVI and FOS+COL, and showed that bacterial regrowth observed with FOS, CAZ-AVI, and COL alone was suppressed in combination therapy. Conclusions: FOS-based combinations, particularly with CAZ-AVI and COL, demonstrated potent synergistic activity against MBL-producing K. pneumoniae and P. aeruginosa, supporting their potential utility in rational combination therapies for infections due to MBL-producing bacteria.<\/jats:p>","DOI":"10.3390\/antibiotics14121247","type":"journal-article","created":{"date-parts":[[2025,12,10]],"date-time":"2025-12-10T12:20:57Z","timestamp":1765369257000},"page":"1247","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["In Vitro Evaluation of Fosfomycin Combinations Against Metallo-\u03b2-Lactamase-Producing Klebsiella\u00a0pneumoniae and Pseudomonas\u00a0aeruginosa Clinical Isolates"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9756-7385","authenticated-orcid":false,"given":"Esther","family":"Wohlfarth","sequence":"first","affiliation":[{"name":"Antiinfectives Intelligence GmbH, 51105 Cologne, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5843-4819","authenticated-orcid":false,"given":"Aur\u00e9lien","family":"Dinh","sequence":"additional","affiliation":[{"name":"Infectious Disease Department, University Hospital Raymond-Poincar\u00e9, 92380 Garches, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4766-8238","authenticated-orcid":false,"given":"Georgia","family":"Vrioni","sequence":"additional","affiliation":[{"name":"Department of Microbiology, Medical School, National and Kapodistrian University of Athens, 11527 Athens, Greece"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9386-8885","authenticated-orcid":false,"given":"Dorota","family":"\u017babicka","sequence":"additional","affiliation":[{"name":"Department of Epidemiology and Clinical Microbiology, National Medicines Institute, 00725 Warsaw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mariano","family":"Bernardo","sequence":"additional","affiliation":[{"name":"Microbiology and Virology Unit, Cotugno Hospital, Azienda Ospedaliera dei Colli, 80131 Naples, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9625-6024","authenticated-orcid":false,"given":"Carlo","family":"Tascini","sequence":"additional","affiliation":[{"name":"Department of Medicine (DMED), Infectious Diseases Clinic, University of Udine, 56100 Udine, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Latifa","family":"Noussair","sequence":"additional","affiliation":[{"name":"Microbiology Department, University Hospital Raymond-Poincar\u00e9, 92380 Garches, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Christian","family":"Mayer","sequence":"additional","affiliation":[{"name":"InfectoPharm Arzneimittel und Consilium GmbH, 64646 Heppenheim, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,10]]},"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 (WHO) (2025, October 14). 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