Metronidazole Susceptibility Patterns in European Bacteroides, Phocaeicola, and Parabacteroides Clinical Isolates-A Systematic Review and Meta-Analysis.

Objectives: This study aimed to provide an updated overview of metronidazole susceptibility among human clinical isolates of Bacteroides, Phocaeicola, and Parabacteroides in Europe based on EUCAST breakpoint interpretation. Methods: A systematic review and meta-analysis were undertaken following searches of Web of Science, MEDLINE/PubMed, and Embase for studies published between 2011 and 2025. Eligible studies reported metronidazole susceptibility data, including minimum inhibitory concentrations and/or susceptible/resistant proportions, for clinical isolates from European countries. Risk of bias was assessed using criteria adapted from the Joanna Briggs Institute critical appraisal tool. Random-effects meta-analysis of proportions was used to estimate pooled susceptibility, with heterogeneity quantified by I2 and τ2; 95% prediction intervals and country subgroup analyses were also performed. Small-study effects were evaluated by funnel plot inspection, Egger's and Begg's tests. Results: Thirty-eight studies, comprising 72 country-specific datasets and 8501 isolates, were included. The pooled susceptibility proportion was 99.81% (95% CI 99.44-99.99%), with substantial heterogeneity (I2 = 68.2%; τ2 = 0.0038). The 95% prediction interval ranged from 95.75% to 100%. Although between-country differences were statistically significant, susceptibility remained consistently high overall. Lower values in Portugal and Switzerland came from single small datasets. Conclusions: These findings support the sustained in vitro activity of metronidazole across Europe, while highlighting the need for continued surveillance, particularly in underrepresented settings.