14 The role of gut bacteria in peristomal skin complications

Aim An ostomy is a surgically created percutaneous aperture from a hollow organ to the abdominal wall, facilitating the expulsion of waste products, termed dejecta. While an ostomy can be lifesaving, circumventing compromised organs of the gastrointestinal system, it is commonly associated with damage to the skin surrounding the ostomy, termed peristomal skin complications (PSCs). The greatest risk factor for PSCs is dejecta leakage onto the skin, particularly in an ileostomy, a diversion of the small intestine, presumed to be due to high pancreatic enzyme and bile acid concentrations. However, the active constituents of ileostomy dejecta, particularly the dejecta microbiota, are poorly understood. This project aims to address this knowledge gap by creating in vitro skin models to elucidate the role of dejecta bacteria in PSC-related injury. Methods Ileostomy dejecta collected from 7 patients was cultured in aerobic and anaerobic conditions to establish bacterial dominances. Species were quantified using viable plate count and identified by MALDI-TOF mass spectrometry. Skin-equivalent models (SEMs), comprising human dermal fibroblasts in a collagen gel with a stratified HaCaT keratinocyte layer, were cultivated for 21 days. PSCs were mimicked by applying filter paper saturated with dejecta onto the SEMs for 24 h. To quantify the contribution of bacteria, samples underwent disinfection (filtration, penicillin-streptomycin treatment, and freeze-thaw cycles) to reduce the viable bacterial load, and were compared to the respective raw/untreated sample effect on the SEMs by histological analysis. Results Bacterial culture has revealed unique individual microbiome profiles, with 33 distinct species identified across 7 patient dejecta samples. These cultures revealed a dominance of facultative anaerobic species (61%), with Escherichia coli, Enterococcus faecium, and Klebsiella species predominating. The remaining species were identified as obligate anaerobes (18%) and aerotolerant anaerobes (21%). The relative percentage abundance of Gram-positive to Gram-negative species across donors favored Gram-positive species (5:4). SEM formation, with distinct dermal and epidermal layers, was confirmed by histology. Preliminary testing showed application of raw ileostomy dejecta caused significant damage to the SEMs, characterized by epidermal erosion and disruptions in the dermal matrix on histology. Disinfection of the dejecta was accomplished using a combination of 0.45 μm syringe filtration, a 1-hour treatment with 10% penicillin-streptomycin, and two freeze-thaw cycles at −20°C, which collectively reduced the bacterial load by approximately 98–99% on culture. Upon application of the disinfected dejecta, the SEMs showed a reduced degree of damage, with better preservation of skin structure. Conclusions The distinction between the effects of raw and disinfected dejecta demonstrates that bacterial presence accelerates skin damage, although the precise mechanism remains uncertain. Interestingly, several of the bacterial species isolated are known to produce proteases that can degrade skin proteins, which may contribute to the development of PSCs (for example E. faecium produces gelatinase, capable of cleaving denatured collagen). Insights from this project may inform the development of future therapies to mitigate PSCs for patients with ileostomies by elucidating the microbial dynamics occurring at the unique gut-skin interface created by an ostomy.