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.