Development of an in vitro model for testing novel antimicrobial substances

Abstract

Chronic or hard to heal wounds are very susceptible to infections. Due to the biofilm mode of growth in these wound, conventional therapies, such as antibiotics, do not eradicate the bacteria. New therapeutics must be developed to be able to combat these infections and one way might be to control or inhibit bacterial communication, so called quorum sensing. Possible quorum sensing inhibitors can be antagonist to the quorum sensing signaling. Developing an in vitro model that mimics biofilm infection in chronic wounds will enable new treatment strategies to be evaluated. It will also allow for optimization of the antimicrobial effect and safety of the compound before testing in animal models. In this in vitro model, cultures of monocyte derived macrophages on collagen coated surfaces were exposed to conditioned media from Pseudomonas aeruginosa, a well documented biofilm former and present in more than 50% of all chronic wounds. Four different clinically isolated strains from chronic wounds and one laboratory strain, PAO1, were assessed based on their effect on macrophage viability and cytokine response. The different strains were characterized as more virulent strains or less virulent strains. The results from the study showed that a well established biofilm from the less virulent bacteria tend to induce an anti-inflammatory response in the cells while biofilm from the more virulent seemed to induce a pro-inflammatory response. The model was then evaluated by testing the effect of salicylic acid on bacterial virulence. The results indicated that bacteria cultured together with salicylic acid moved towards a less virulent phenotype. These first studies in the development of an in vitro model show promising results, however, more work must be done to further develop the model, before it is fully functional.