The ability of polymicrobial biofilms to promote wound infection chronicity
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Chronic wound infections have a profound effect on the morbidity and mortality of a large patient population and cost billions of dollars in direct medical costs annually in the United States. Chronic wound infections are typically polymicrobial and biofilm-associated, however little is known about how they affect the host immune system and impair the healing process. This project was designed to compare single versus polymicrobial biofilm infections in a murine chronic wound model. We hypothesized that multispecies bacterial biofilms, or communities of bacteria that reside in a polysaccharide shell, contribute to the severity and antibacterial resistance of wounds. To test this hypothesis we developed a chronic-wound mouse model to determine the ability of multispecies bacterial biofilms to increase wound chronicity in biofilm-associated infections. Multispecies biofilms consisting of both gram negative and gram positive strains, as well as aerobes and anaerobes, were grown in vitro and then transplanted onto the wounds of mice. These in vitro-to-in vivo multispecies biofilm transplants generated polymicrobial wound infections, which remained heterogeneous with all four bacterial species throughout the experiment. In support of our hypothesis, we observed that wounded mice given multispecies biofilm infections displayed impaired wound healing over non-infected mice, or mice infected with a single species of bacteria. In addition, the bacteria in the polymicrobial wound biofilms displayed increased antimicrobial tolerance in comparison to those in single species biofilms. These data suggest that synergistic interactions between different bacterial species in wounds may contribute to healing delays and/or antibiotic tolerance.