Ankle brachial indices and anaerobes: is peripheral arterial disease associated with anaerobic bacteria in diabetic foot ulcers?

Background: Lower extremity amputations from diabetic foot ulcers (DFUs) are rebounding, and new biomarkers that predict wound healing are urgently needed. Anaerobic bacteria have been associated with persistent ulcers and may be a promising biomarker beyond currently recommended vascular assessments. It is unknown whether anaerobic markers are simply a downstream outcome of peripheral arterial disease (PAD) and ischemia, however. Here, we evaluate associations between two measures of anaerobic bacteria-abundance and metabolic activity-and PAD.

Methods: We built a prospective cohort of 37 patients with baseline ankle brachial index (ABI) results. Anaerobic bacteria were measured in two ways: DNA-based total anaerobic abundance using 16S rRNA gene amplicon sequencing and resulting summed relative abundance, and RNA-based metabolic activity based on bacterial read annotation of metatranscriptomic sequencing. PAD was defined three ways: PAD diagnosis, ABI results, and a dichotomous definition of mild ischemia (versus normal) based on ABI values. Statistical associations between anaerobes and PAD were evaluated using univariate odds ratios (ORs) or Spearman's correlations.

Results: Total anaerobe abundance was not significantly associated with PAD diagnosis, ABI results, or mild ischemia (OR_PAD = 0.47, 95% CI = 0.023-7.23, p = 0.60; Spearman's correlation coefficient_ABI = 0.24, p = 0.17; OR_{mild ischemia} = 0.25, 95% CI = 0.005-5.86, p = 0.42). Anaerobic metabolic activity was not significantly associated with PAD diagnosis, ABI results, or mild ischemia (OR_PAD = 1.99, 95% CI = 0.17-21.44, p = 0.57; Spearman's correlation coefficient_ABI = 0.12, p = 0.52; OR_{mild ischemia} = 0.90, 95% CI = 0.03-15.16, p = 0.94).

Conclusion: Neither anaerobic abundance nor metabolic activity was strongly associated with our three definitions of PAD. Therefore, anaerobic bacteria may offer additional prognostic value when assessing wound healing potential and should be investigated as potential molecular biomarkers for DFU outcomes.