In vitro and in vivo Models of Biofilm-Mediated Infections

Abstract

Biofilms are microbial communities encased in a matrix of polysaccharides, extracellular DNA, and proteins. When growing in biofilms, bacteria display increased resistance to immune clearance and antibiotic tolerance. For these reasons, biofilms are responsible for many chronic infections. Treatment of biofilm-mediated infections is challenging, and often requires surgical debridement and/or lengthy courses of antibiotics. In order to develop more effective treatment strategies and therapeutics, it is important to develop and utilize model systems that incorporate the biofilm phenotype. In this dissertation, we describe the use of a rabbit model of internal fixation to evaluate the use of prophylactic antibiotic powders in surgery, characterize Scnn1b-Tg mice as models of Pseudomonas aeruginosa and Staphylococcus aureus infections in cystic fibrosis lungs, and use a continuous flow biofilm reactor to study the interactions of S. aureus and P. aeruginosa in chronic biofilms. We found that tobramycin powder is able to prevent surgical site infection with tobramycin-resistant Enterobacter cloacae, demonstrating the potential utility of antibiotic powders in preventing infections in orthopedic surgery. We also found that Scnn1b-Tg mice clear infections with P. aeruginosa and S. aureus more slowly than wildtype littermates. When Scnn1b-Tg mice were infected with a mucoid CF isolate, bacterial aggregates like those observed in cystic fibrosis patients’ sputum were found in the lungs, illustrating the potential of Scnn1b-Tg mice as models of cystic fibrosis lung infection. Finally, we found that P. aeruginosa modifies the structure of its lipid A by adding 4-amino-4-deoxy-L-arabinose (Ara4N) to the terminal phosphates when introduced to established S. aureus biofilms. The addition of Ara4N is associated with resistance to polymyxin antibiotics, such as colistin. This finding represents a potential mechanism by which interactions in polymicrobial biofilms can lead to changes in antibiotic resistance. These studies illustrate the importance of incorporating biofilm models when developing treatments for biofilm-mediated infections.