(A) Stickland metabolism consists of anaerobic amino acid fermentation through coupled oxidation and reduction pathways. In the reductive pathway, amino acids are first deaminated to form 2-hydroxy acids and then reduced to carboxylic acids. In the oxidative pathway, amino acids are deaminated and oxidized with loss of CO₂ to yield a distinct set of carboxylic acids. Depicted here are established Stickland substrates and products identified within patient fecal metabolomes. Stickland substrates include the nonproteinogenic amino acid ornithine. ND, not determined. (B) Heatmap of Stickland precursor and product abundances corresponding to patient fecal metabolomes from the 3 diagnostic groups. Metabolites were organized using unsupervised hierarchical clustering. Metabolites differing significantly (Mann-Whitney U test; *P < 0.05, ***P < 0.001) between Cx^–/EIA^– and Cx⁺/EIA⁺ groups are labeled, along with the direction of the difference relative to the Cx^–/EIA^– control group. Stickland products are labeled according to the color scheme in A. (C) Adjusted and unadjusted (crude) CDI odds ratios and confidence intervals (95%) for Stickland precursors and products. Odds ratios were estimate by fitting logistic regression models to each of 2000 bootstrap samples stratified on Cx/EIA status (Cx^–/EIA^– vs. Cx⁺/EIA⁺). Logistic models containing a single metabolite were fit to obtain crude odds ratios (red). A single logistic model including all metabolites was fit to obtain the adjusted odds ratios (green). Bars represent 95% bootstrap percentile confidence intervals and black dots represent median odds ratios across all bootstrap samples. Stickland products are labeled according to the color scheme in A.