The study selected 2124 SNPs as IVs for 196 bacterial taxa and 7355 SNPs as IVs for 91 inflammatory proteins. The
F statistics of all selected IVs were >10, indicating statistical potency and IVs’ reliability. A total of 26 GM (including 3 classes, 3 orders, 7 families, and 13 genera) were causally associated with GO (
Supplementary Table S2). Among them, 10 bacteria were causally associated with GO in at least two MR methods (
Table 1;
Fig. 2). Specifically, the following six bacteria were protective factors against GO: class Deltaproteobacteria (odds ratio [OR] = 0.54; 95% confidence interval [CI], 0.36–0.81;
P = 0.003), class Negativicutes (OR = 0.49; 95% CI, 0.25–0.96;
P = 0.038), order Desulfovibrionales (OR = 0.56; 95% CI, 0.36–0.86;
P = 0.008), order Selenomonadales (OR = 0.49; 95% CI, 0.25–0.96;
P = 0.038), genus
Parabacteroides (OR = 0.29; 95% CI, 0.16–0.51;
P < 0.001), and genus
Ruminococcaceae_UCG_011 (OR = 0.69; 95% CI, 0.51–0.94;
P = 0.018). Conversely, the following four bacteria were identified as risk factors for GO: family Prevotellaceae (OR = 1.96; 95% CI, 1.18–3.26;
P = 0.010), family Streptococcaceae (OR = 1.82; 95% CI, 1.11–2.98;
P = 0.017), genus
Lachnospiraceae_UCG_010 (OR = 1.82; 95% CI, 1.14–2.90;
P = 0.012), and genus
Tyzzerella3 (OR = 1.40; 95% CI, 1.13–1.75;
P = 0.003). Post-FDR adjustment showed the protective effect of a higher abundance of the genus
Parabacteroides on GO (
P = 0.004). The reliability of the results was further confirmed by the consistency of weighted median and maximum likelihood methods with the IVW trend in MR analysis. Cochran's
Q test showed no heterogeneity. MR-PRESSO indicated potential horizontal pleiotropy in class Negativicutes and order Selenomonadales, while MR-Egger found potential horizontal pleiotropy in the family Prevotellaceae. These findings suggest the need to carefully interpret research results to ensure their reliability and accuracy. The leave-one-out analysis showed that removing a particular SNP would not change the causal estimates (
Supplementary Fig. S1). Steiger's test confirmed that the direction of causal association is correct.