Long-Term Daily Chlorhexidine Foot Cleansing Reduces Staphylococcal Burden on the Feet of People with Prior Diabetic Foot Complications

In a randomized controlled trial involving people with diabetes and prior foot complications, daily chlorhexidine foot cleansing for one year significantly reduced *Staphylococcus* abundance and durably altered skin microbiota, though these microbial changes alone were insufficient to prevent new diabetic foot ulcers.

The Gist

The Big Picture: A Garden on Your Feet

Imagine the skin on your feet is like a small, busy garden. For people with diabetes, this garden can sometimes get out of balance. Specifically, a certain type of "weed" called Staphylococcus (a common bacteria) can take over, crowding out other helpful plants. This imbalance is linked to foot sores (ulcers) that are hard to heal.

The researchers wanted to know: If we use a strong antiseptic soap (chlorhexidine) to wash these feet every day for a year, will it clear out the "weeds" and help the garden stay healthy?

The Experiment: Two Types of Soap

The study involved 87 veterans with diabetes who had previously had foot problems. They were split into two groups, like two teams in a game:

1. Team Chlorhexidine: Used wipes with a powerful antiseptic soap every day.
2. Team Soap-and-Water: Used wipes with regular soap and water every day.

Both groups washed their feet daily for 12 months. The researchers took "snapshots" (swabs) of the bacteria on their feet at the start, after 3 months, after 12 months, and even a month after they stopped washing with the special wipes.

What They Found: The "Weed" Killer Works

The results showed that the antiseptic soap (chlorhexidine) was much more effective at changing the foot garden than the regular soap.

• Clearing the Crowd: The antiseptic group saw a huge drop in the total number of bacteria. It was like mowing a lawn that was overgrown with tall grass; the grass got much shorter and less dense.
• Targeting the Weeds: The most important change was that the Staphylococcus "weeds" were significantly reduced. In the antiseptic group, these bacteria dropped from making up about 63% of the garden to much lower levels. The regular soap group saw a tiny drop, but it wasn't as dramatic.
• More Variety: Surprisingly, while the total number of bacteria went down, the variety of different types of bacteria actually went up. Think of it like clearing a field of one dominant weed so that many different types of wildflowers can finally grow.
• The "Hangover" Effect: Even after the participants stopped using the antiseptic wipes for a month, their feet still had fewer "weeds" and a more diverse garden compared to where they started. The effect lasted longer than the treatment itself.

The Twist: A Cleaner Garden Didn't Stop the Sores

Here is the tricky part. Even though the antiseptic soap successfully cleaned the garden and reduced the "weeds," it did not stop new foot sores from forming.

The researchers found that the group using the powerful soap had the exact same rate of new foot ulcers as the group using regular soap.

Why? The paper suggests that while cleaning the garden is good, foot sores in people with diabetes are caused by a mix of many factors (like poor blood flow and nerve damage), not just bacteria. Simply removing the "weeds" wasn't enough to fix the whole problem.

What About Fungi?

The researchers also checked for fungi (like yeast or mold) in the garden. They found that neither the antiseptic soap nor the regular soap made any significant difference to the fungal population. The fungi stayed the same regardless of what soap was used.

The Bottom Line

Using a strong antiseptic soap every day is like using a very effective weed killer: it successfully reduces the bad bacteria (Staphylococcus) and makes the foot skin environment more diverse, and these changes last for a while even after you stop using it.

However, just because the garden is cleaner doesn't mean the fence (the skin barrier) won't break. For people with diabetes, cleaning the feet is a good step, but it isn't a magic shield that prevents foot sores on its own. You need more than just a clean garden to keep the whole system healthy.

Technical Summary

Technical Summary: Long-Term Daily Chlorhexidine Foot Cleansing Reduces Staphylococcal Burden on the Feet of People with Prior Diabetic Foot Complications

Problem Statement
Individuals with diabetes face a persistent risk of diabetic foot ulcer (DFU) recurrence, even after initial healing, with nearly 40% of ulcers recurring within the first year. This high recurrence rate is attributed to underlying pathophysiologic factors such as neuropathy and peripheral arterial disease, but the role of the skin microbiome remains a critical, yet incompletely understood, factor. Dysbiosis and an increased load of Staphylococcus aureus have been associated with impaired wound healing and ulcer formation. While topical chlorhexidine gluconate (CHG) is a broad-spectrum antiseptic used to reduce microbial burden, a prior randomized clinical trial (RCT) by the same authors found that daily CHG foot cleansing did not statistically significantly reduce new DFU rates compared to soap-and-water. Consequently, the specific, durable effects of long-term CHG use on the foot skin microbiota—specifically bacterial bioburden, diversity, and community composition—required further evaluation to determine if the intervention produced meaningful microbiological shifts despite the lack of immediate clinical ulcer prevention.

Methodology
This study was a secondary analysis of a single-center, double-blind, placebo-controlled, phase 2b randomized clinical trial conducted at the Baltimore Veterans Affairs Medical Center (2019–2023).

• Cohort: 87 ambulatory adult veterans with diabetes and a history of resolved foot complications (chronic ulcer, infection, or partial amputation) but no current active wounds.
• Intervention: Participants were randomized 1:1 to daily foot cleansing with either 2% chlorhexidine gluconate wipes or soap-and-water wipes for 12 months.
• Sampling: Foot swabs (eSwabs) were collected from the right foot pad at four timepoints: baseline (pre-intervention), 3 months, 12 months, and 4 weeks post-treatment cessation.
• Microbiological Analysis:
  • Bacterial Bioburden: Quantified using digital PCR (dPCR) targeting the 16S rRNA gene (V3–V4 region).
  • Microbiota Composition: Assessed via 16S rRNA amplicon sequencing (bacteria) and ITS1 amplicon sequencing (fungi).
  • Data Processing: Sequencing data underwent rigorous quality control (trimming, denoising with DADA2, chimera removal) and were clustered into Operational Taxonomic Units (OTUs). Taxonomic classification utilized SILVA (bacteria) and UNITE+INSD (fungi) databases.
  • Statistical Analysis: Diversity metrics (Shannon index, observed richness) and community composition (Bray–Curtis dissimilarity, NMDS, PERMANOVA) were analyzed using R. Bioburden and relative abundance changes were assessed using Wilcoxon rank-sum tests with Holm–Bonferroni adjustments.

Key Contributions and Results
The study provides a high-resolution, longitudinal assessment of how daily antiseptic use alters the foot microbiome in a high-risk diabetic population.

1. Reduction in Bacterial Bioburden: CHG treatment resulted in a statistically significant reduction in total bacterial bioburden compared to baseline. At 3 months, the average 16S log10 concentration dropped from 2.55 to 1.78 ($p < 0.0001$). While bioburden increased slightly by month 12 and returned to near-baseline levels 4 weeks post-treatment, the reduction was sustained for the majority of the treatment period. Soap-and-water treatment showed similar trends but lacked statistical significance due to high inter-patient variability.
2. Increased Microbial Diversity: Contrary to the hypothesis that antiseptics might reduce diversity, CHG treatment significantly increased both observed species richness and Shannon diversity compared to baseline ($p < 0.001$ at 3 months). This increase persisted through 12 months but diminished after treatment cessation. Soap-and-water showed a similar, though less pronounced, trend.
3. Specific Suppression of Staphylococcus: The most distinct finding was a sustained, significant reduction in the relative abundance of Staphylococcus (the dominant genus) in the CHG group. Baseline abundance was ~63%; after 3 months of CHG, 83% of patients showed a ~30% reduction. This suppression persisted through 12 months, with a significant reduction still observed 4 weeks post-treatment. In contrast, the soap-and-water group showed non-significant, smaller fluctuations.
4. Community Composition Shifts: PERMANOVA analysis confirmed that CHG treatment caused a significant, consistent directional shift in the core microbiome composition ($p < 0.001$, $R^2 = 0.090$), clustering samples by active treatment status. This shift was not observed in the soap-and-water group.
5. Fungal Microbiome: No significant shifts in fungal community composition, diversity, or relative abundance were detected for either treatment group over the study duration.
6. Durability: Several microbiota changes, including reduced bioburden and Staphylococcus abundance, persisted for up to one month after the cessation of daily CHG application.

Significance and Claims
The paper concludes that daily chlorhexidine foot cleansing effectively and durably modifies the foot skin microbiota in individuals with diabetes and prior foot complications. Specifically, it demonstrates that CHG is superior to soap-and-water in reducing total bacterial bioburden and suppressing Staphylococcus abundance, with effects lasting beyond the active treatment period.

However, the authors maintain a modest stance regarding clinical translation. They explicitly state that while the microbiological changes are robust and durable, these alterations did not translate into a statistically significant reduction in new diabetic foot ulcers in the parent trial. The paper posits that lowering bacterial bioburden and Staphylococcus load alone may be insufficient to prevent ulcer recurrence in this population, suggesting that ulcer prevention likely requires multi-faceted interventions addressing physiological and nutritional factors alongside microbiome modulation.

The study highlights the potential utility of CHG for populations at risk of staphylococcal infections (e.g., reducing colonization prior to potential ulceration or infection) but cautions against assuming that microbiome alteration alone is a panacea for DFU recurrence. The findings support the feasibility of long-term structured foot hygiene and suggest that less-than-daily CHG use might still confer benefits due to the persistence of microbiota changes.