Understanding the physiology of Pseudomonas aeruginosa biofilms in an in vitro chronic wound model

Abstract

Pseudomonas aeruginosa is a common colonizer of cutaneous abrasions and burns. These Gram-negative, aerobic bacteria are problematic due to their natural resilience to antibiotics and their metabolic versatility. P. aeruginosa can produce a prodigious extracellular matrix. Within this matrix P. aeruginosa can divide and form a multicellular community called a biofilm. Biofilms have become a health concern worldwide, as these communities are highly resistant to antibiotics. This thesis reports the effort to model the wound environment. A chronic wound exudate medium was designed and P. aeruginosa was grown at 33°C under low flow in a drip-flow biofilm reactor. Bacterial cells were grown planktonically and in biofilms. Biofilms were treated with the fluoroquinone, ciprofloxacin for 24 hours and transcriptomic and metabolomic data were collected from treated and untreated biofilms and planktonic cells. Cells growing in biofilms demonstrated a shift in in the regulation of their tricarboxylic acid cycle, amino acid degradation, and siderophore biosynthesis genes as compared to planktonic cells. Ciprofloxacin treatment altered the transcriptomic landscape within the biofilm. Changes were observed in the transcription of DNA repair, prophage, and phenazine biosynthesis genes. An important virulence factor, the type VI secretion system, was also differently regulated in these samples and is likely important for the persistent infection of wounds. From the information collected, target genes have been identified for future gene-knockout and ciprofloxacin susceptibility assays. A reduction in fitness may indicate genes that are relevant drug targets to enhance antibiotic treatment of these resilient communities.