{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,7]],"date-time":"2026-09-07T10:52:50Z","timestamp":1788778370822,"version":"build-2803163510"},"reference-count":30,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2025,2,5]],"date-time":"2025-02-05T00:00:00Z","timestamp":1738713600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"United Kingdom Health Security Agency (Juno project)"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Antibiotics"],"abstract":"<jats:p>Background: Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of neonatal sepsis in high-income countries. While intrapartum antibiotic screening reduces this risk, increasing resistance to macrolides and lincosamides in Europe since the 1990s has limited therapeutic options for penicillin-allergic patients. Reports of reduced beta-lactam susceptibility in GBS further emphasise the need for robust antimicrobial resistance (AMR) surveillance. However, broth microdilution (BMD) methods are unsuitable for large-scale antimicrobial susceptibility testing (AST). Objective: To demonstrate that agar-dilution AST provides equivalent results to broth dilution methods, with superior capacity for high-throughput screening. Methods: Agar-dilution and microdilution AST methods were compared using a panel of 24 characterised susceptible and resistant GBS strains for benzylpenicillin, chloramphenicol, clindamycin, erythromycin, gentamicin, levofloxacin, tetracycline, and vancomycin. Minimum inhibitory concentration (MIC) agreements were evaluated, and resistance profile correlations were assessed using Cohen\u2019s kappa values. Results: Agar-dilution demonstrated &gt;90% agreement with BMD MIC for most antimicrobials, except vancomycin (87.5%), erythromycin (83.33%), and tetracycline (52.78%). Cohen\u2019s kappa values indicated strong agreement (0.88\u20131.00) for resistance determination. Agar-dilution avoided \u201ctrailing growth\u201d issues associated with BMD and facilitated easier detection of non-GBS contaminants. Conclusions: Agar-dilution is a valid method for high-throughput AMR surveillance of retrospective cohorts (96 isolates per plate) and is critical for identifying emerging GBS resistance trends and informing therapeutic guidelines. However, due to the large number of plates required per antimicrobial, it is impractical for routine clinical diagnostics.<\/jats:p>","DOI":"10.3390\/antibiotics14020156","type":"journal-article","created":{"date-parts":[[2025,2,5]],"date-time":"2025-02-05T05:50:36Z","timestamp":1738734636000},"page":"156","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Agar-Dilution Is Comparable to Broth Dilution for MIC Determination in Streptococcus agalactiae"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2142-3443","authenticated-orcid":false,"given":"Edward A. R.","family":"Portal","sequence":"first","affiliation":[{"name":"Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff University, Cardiff CF14 4XN, UK"},{"name":"Department of Biology, Ineos Oxford Institute of Antimicrobial Research, University of Oxford, Oxford OX1 3RE, UK"},{"name":"Reference Microbiology Division, United Kingdom Health Security Agency, London NW9 5EQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-5309-2991","authenticated-orcid":false,"given":"Caitlin","family":"Farley","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff University, Cardiff CF14 4XN, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-5985-6704","authenticated-orcid":false,"given":"Teresa","family":"Iannetelli","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff University, Cardiff CF14 4XN, UK"},{"name":"Department of Biology, Ineos Oxford Institute of Antimicrobial Research, University of Oxford, Oxford OX1 3RE, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juliana","family":"Coelho","sequence":"additional","affiliation":[{"name":"Reference Microbiology Division, United Kingdom Health Security Agency, London NW9 5EQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Androulla","family":"Efstratiou","sequence":"additional","affiliation":[{"name":"Reference Microbiology Division, United Kingdom Health Security Agency, London NW9 5EQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephen D.","family":"Bentley","sequence":"additional","affiliation":[{"name":"Parasites and Microbes, Wellcome Sanger Institute, Cambridge CB10 1SA, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Victoria J.","family":"Chalker","sequence":"additional","affiliation":[{"name":"Reference Microbiology Division, United Kingdom Health Security Agency, London NW9 5EQ, UK"},{"name":"Office of the Chief Scientific Officer for the UK, London SE1 8UG, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9117-6911","authenticated-orcid":false,"given":"Owen B.","family":"Spiller","sequence":"additional","affiliation":[{"name":"Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff University, Cardiff CF14 4XN, UK"},{"name":"Reference Microbiology Division, United Kingdom Health Security Agency, London NW9 5EQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,2,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"S200","DOI":"10.1093\/cid\/cix664","article-title":"Estimates of the Burden of Group B Streptococcal Disease Worldwide for Pregnant Women, Stillbirths, and Children","volume":"65","author":"Seale","year":"2017","journal-title":"Clin. 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