A Comparative Study of the Microenvironment of an In Vitro Chronic Wound Model and an Ex Vivo Porcine Model - An Evaluation Employing Human Chronic Wound Data

Aim: Chronic wounds are often found infected with aggregated bacteria growing in an extracellular matrix providing protection against the host immune response and antibiotics. Eradication of biofilm, as a part of wound healing treatments, is challenging and several laboratory models have been established to study biofilm growth and for testing eradication strategies including in vitro, ex vivo, and in vivo models. However, it is unknown to which extend these models mimic the conditions of chronic wounds. The aim of this study was to explore whether two dual-species models reflect the conditions in human chronic wounds concerning growth conditions of the infecting microorganisms.
Method: A novel in vitro model and an ex vivo porcine model employing Staphylococcus aureus and Pseudomonas aeruginosa were investigated by means of growth at different temperatures, and measurements of pH and oxygen micro profiles. Parameters were evaluated against published data profiles and through statistical analyses.
Results/Discussion: Stable co-existence of P. aeruginosa and S. aureus was confirmed for both the in vitro models and the ex vivo model using cell count methods and statistical analyses showed that the effect of temperature is species dependent. Confocal laser scanning microscopy confirmed the presence of bacterial aggregates of various sizes in the in vitro models corresponding to in vivo findings. In vivo tendencies were demonstrated for both the in vitro and ex vivo models with oxygen and pH microprofiles, demonstrating steep oxygen gradients reaching anoxic conditions and slightly alkaline environments, respectively.