Portal Edward A R, Farley Caitlin, Iannetelli Teresa, Coelho Juliana, Efstratiou Androulla, Bentley Stephen D, Chalker Victoria J, Spiller Owen B
Division of Infection and Immunity, Department of Medical Microbiology, University Hospital of Wales, Cardiff University, Cardiff CF14 4XN, UK.
Department of Biology, Ineos Oxford Institute of Antimicrobial Research, University of Oxford, Oxford OX1 3RE, UK.
Antibiotics (Basel). 2025 Feb 5;14(2):156. doi: 10.3390/antibiotics14020156.
(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).
To demonstrate that agar-dilution AST provides equivalent results to broth dilution methods, with superior capacity for high-throughput screening.
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's kappa values.
Agar-dilution demonstrated >90% agreement with BMD MIC for most antimicrobials, except vancomycin (87.5%), erythromycin (83.33%), and tetracycline (52.78%). Cohen's kappa values indicated strong agreement (0.88-1.00) for resistance determination. Agar-dilution avoided "trailing growth" issues associated with BMD and facilitated easier detection of non-GBS contaminants.
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.
B族链球菌（GBS）是高收入国家新生儿败血症的主要病因。虽然产时抗生素筛查可降低这种风险，但自20世纪90年代以来，欧洲对大环内酯类和林可酰胺类药物的耐药性不断增加，限制了青霉素过敏患者的治疗选择。GBS对β-内酰胺类药物敏感性降低的报告进一步凸显了进行强有力的抗菌药物耐药性（AMR）监测的必要性。然而，肉汤微量稀释（BMD）方法不适用于大规模抗菌药物敏感性试验（AST）。
证明琼脂稀释法AST与肉汤稀释法结果相当，且具有更高的高通量筛选能力。
使用一组24株已鉴定的对苄青霉素、氯霉素、克林霉素、红霉素、庆大霉素、左氧氟沙星、四环素和万古霉素敏感及耐药的GBS菌株，比较琼脂稀释法和微量稀释法AST。评估最低抑菌浓度（MIC）一致性，并使用科恩kappa值评估耐药谱相关性。
除万古霉素（87.5%）、红霉素（83.33%）和四环素（52.78%）外，琼脂稀释法对大多数抗菌药物的MIC与BMD显示出>90%的一致性。科恩kappa值表明在耐药性判定方面有很强的一致性（0.88 - 1.00）。琼脂稀释法避免了与BMD相关的“拖尾生长”问题，便于更轻松地检测非GBS污染物。
琼脂稀释法是对回顾性队列（每板96株分离株）进行高通量AMR监测的有效方法，对于识别GBS新出现的耐药趋势和为治疗指南提供依据至关重要。然而，由于每种抗菌药物需要大量平板，因此对于常规临床诊断不实用。
