Abstract
Sex-specific differences in the oral microbiome may contribute to variability in Coronavirus disease 2019 (COVID-19) severity, yet their influence on oral microbial composition and predicted function remains unknown. To address this gap, this study investigated whether distinct sex-specific patterns exist in microbial taxonomic and functional diversity across COVID-19 severity levels in a Mexican saliva cohort. We hypothesized that the taxa driving dysbiosis would differ by sex due to host genetic variances and predicted that the overall severity of dysbiosis would be higher in males compared to females of the same severity level. Furthermore, we hypothesized that males with severe infection would exhibit stronger enrichment of inflammatory pathways, such as lipopolysaccharide (LPS) biosynthesis and antimicrobial resistance genes. Microbial composition and diversity were characterized through secondary analysis of 16S ribosomal RNA (rRNA) sequencing data using alpha and beta diversity analyses, indicator species analysis, and differential abundance testing, while predicted functional pathways were inferred using PICRUSt2. Alpha diversity showed no sex associated differences at any severity levels, whereas beta diversity indicated that sex contributed to variance only in severe cohorts. Indicator Species Analysis (ISA) identified distinct mortality signatures, with deceased males associated with Acinetobacter and deceased females characterized by Veillonella and Isobaculum. Differential abundance testing revealed sex-specific dysbiosis increased with disease severity, with males exhibiting greater enrichment in non-commensal genera in severe and deceased cohorts. The integrated analysis highlighted distinct patterns of normalized counts between males and females across severity levels, where males exhibited high loads of opportunistic taxa while females showed depletion as severity increased. Functional inference of MetaCyc pathways indicated that COVID-19 severity was the primary driver of predicted functional variation, whereas sex effects were limited and emerged primarily in Severe positive and Deceased strata. Male-enriched pathways included steroid metabolism, amino acid degradation, and cell envelope-related functions, suggesting heightened microbial functional shifts in severe disease, partially supporting the heightened functional shifts in severe disease. Overall, these findings suggest sex influences oral microbiome composition and predicted functional pathways mainly in severe and fatal cases of COVID-19 infection, especially in males.