Date on Senior Honors Thesis


Document Type

Senior Honors Thesis

Degree Name




Author's Keywords

cystic fibrosis; polymicrobial biofilms; biofilms


Cystic Fibrosis (CF) is the most common lethal genetic disorder in the Caucasian population with an incidence of 1 per 3,000 live births and a median predicted survival of only 47 years. Respiratory failure due to repeated pathological insults to lung tissue by infection is the ultimate cause of mortality in the majority of patients. The lung microenvironment created by CF highly favors colonization by opportunistic pathogens such as Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Burkholderia cenocepacia, and Achromobacter xylosoxidans. Biofilm formation by multiple bacterial species contributes to the chronic, persistent, and difficult to treat nature of CF infections. This study seeks to further the limited understanding of what polymicrobial biofilm interactions may be occurring in the CF lung. Survival assays of bacterial cells grown under biofilm-forming conditions demonstrated that P. aeruginosa survival was inhibited, and no detectable growth occurred for B. cenocepacia or A. xylosoxidans in co-culture with S. maltophilia. Further experimentation including supernatant assays, treatment of biofilms with cell lysate, pH measurements, and laser scanning confocal microscopy have elucidated further hints about the potential mechanisms of this S. maltophilia-mediated inhibition. The presence of live S. maltophilia cells appears to be necessary for A. xylosoxidans inhibition, while B. cenocepacia is inhibited by both live cells and filtered S. maltophilia supernatant. Characterization of these interspecies relationships may further our understanding of how flora composition influences pathogenesis in the CF lung.

Lay Summary

Cystic fibrosis is an inherited life-shortening disease that affects tens of thousands of people worldwide. Early death is usually caused by repeated lung infections from bacteria that form thick mats of cells within the lungs called biofilms. These biofilms are very difficult to get rid of and often consist of multiple types of bacteria, making the process of treating infection even more difficult than it would be normally. This study examines the interaction between several species known to infect cystic fibrosis patients. It was found that the bacteria Stenotrophomonas maltophilia reduces biofilm formation of Pseudomonas aeruginosa, Burkholderia cenocepacia, and Achromobacter xylosoxidans when the species are grown together. This has important implications for how we understand the interaction between different bacteria in cystic fibrosis, and investigation into why these specific interactions occur may give us valuable insight into the progression of cystic fibrosis disease and reveal potential therapeutic applications.