Synergistic Effect of Tryptophan and Erythromycin on Pseudomonas Aeruginosa Biofilm Structure and Dispersal

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen that is responsible for diseases such as cystic fibrosis (CF) in immunocompromised individuals. Outcome of CF is abnormally thickened mucus that causes problems in patient’s respiratory system. This condition affects 2.5 million people in the UK alone with a high rate of mortality by the age of 40. Various methods of treatment to manage CF by dispersion and disassembly of biofilm have been intensively researched. Since as much as 80% of human bacterial infections are biofilm- associated, many researchers have begun investigating therapies that specifically target the biofilm architecture, thereby dispersing the microbial cells into their more vulnerable, planktonic state. Amongst the current methods of controlling CF, biofilm dissociation by the use of a combination of an amino acid and an antibiotic has been investigated in this research. During this study, biofilm formation by P. aeruginosa PAO1 was observed under aerobic conditions in Luria Broth and M63 minimal media at 37°C for a period of 24 hours. The cultures were treated with two isomeric forms of tryptophan at different concentrations (1 mM, 4 mM, and 8 mM). Dispersal and dissociation of the cells in all cultures were investigated and compared with the control after 24 hours. The D isomer of tryptophan at concentrations of 4 mM and 8 mM showed higher rate of dispersion in comparison to the L isomeric form and the control. The effect of tryptophan varied with the medium that was used for biofilm growth. Extracellular polymeric substances (EPS) were extracted from the treated and untreated biofilm and quantified for their main components. Biofilm treated with tryptophan and erythromycin resulted in nearly 70% loss of EPS components in comparison with the control after 5 days of growth.