Abstract

Intestinal microbiome dysbiosis has been associated with transplant-related mortality and graft-versus-host disease in allo-HSCT patients. We assessed how pre-transplant antibiotic and antineoplastic exposures, together with multidrug-resistant colonization, are associated with baseline gut microbiome diversity at allo-HSCT. We conducted a prospective, single-center cohort study at Fundeni Clinical Institute (Bucharest, Romania) between August 2024 and June 2025, enrolling 52 allo-HSCT recipients and 27 healthy controls. Fecal samples were collected before conditioning. Gut microbiome composition was assessed via 16S rRNA gene sequencing and analyzed using QIIME2 and R. Associations were evaluated using Wilcoxon test, multivariable linear regression, and PERMANOVA. Shannon diversity was significantly lower in patients (median 4.71, IQR 3.97–5.44) than in healthy controls (median 6.09, IQR 5.87–6.28; p < 0.001). In bivariate analyses, carbapenem (p adj = 0.02) and oxazolidinone exposure (p adj = 0.005) were associated with reduced diversity, while immunotherapy was associated with higher diversity (p adj = 0.042). Broad-spectrum penicillin (p adj = 0.062) and ESBL colonization (p adj = 0.066) did not reach significance. In the multivariable antibiotic model, although the overall model was statistically significant (model p = 0.039), no individual antibiotic class remained significantly associated with Shannon diversity after adjustment for co-exposures. Beta diversity differed modestly with carbapenem exposure (R2 = 0.033, p = 0.019). Pre-transplant antibiotic exposures were associated with lower gut microbiome diversity at allo-HSCT admission, with patterns consistent with a cumulative rather than a class-specific association. These findings support antibiotic stewardship in pre-transplant care.

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