A study of surface motility and biofilm formation in pseudomonas aeruginosa quorum sensing and photodynamic antimicrobial chemotherapy

Date of Award


Degree Name

Ph.D. in Biology


Department of Biology


Advisor: Jayne B. Robinson


Pseudomonas aeruginosa is an opportunistic pathogen that commonly causes infection in immunocompromised individuals. This bacterium forms complex communities known as biofilms. Biofilm formation is dependent on motility as well as quorum-sensing. In this study, we show that P. aeruginosa surface motility is inhibited in the presence of the quorum-sensing molecule E,E-farnesol. In the presence of E,E-farnesol, there is an 4-fold increase in rhamnolipid production. Because swarming motility is dependent on rhamnolipid production, this increase could account for the inhibition in swarming motility observed in the presence of E,E-farnesol. In addition, the effect of the cationic porphyrin 5,10,15,20-tetrakis(1-methyl-pyridino)-21H,23H-porphine, tetra-p-tosylate salt (TMP) on P. aeruginosa biofilms was examined. Exposure to 225 µM TMP and photoactivation resulted in almost complete killing of biofilm associated cell as well as the detachment of wild-type PAO1 biofilms. In contrast, pqsA mutant biofilms that contain less extracellular DNA remained intact. Our results suggest that the action of photoactivated TMP on P. aeruginosa biofilms is two-fold: direct killing of individual cells within biofilms and detachment of the biofilm from the substratum. There was no evidence of porphyrin toxicity in the absence of light; however, biofilms pretreated with TMP without photoactivation were substantially more sensitive to tobramycin than untreated biofilms.


Pseudomonas aeruginosa infections Treatment, Biofilms, Photochemotherapy, Bacteria Motility

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