Effect of viscosity on biofilm phenotypic expression

Biofilms are adherent colonies of microorganisms growing within a polysaccharide cell surface glycocalyx. Antibiotics and biocides used at concentrations capable of killing planktonic organisms have little effect against biofilms. Bacterial and fungal growth has been observed in various viscous environments. It is hypothesized that a viscous environment could act as a mechanism responsible for the phenotypic expression of physiological factors characteristic of biofilms. The effect of viscosity on growth characteristics, morphology and antibiotic sensitivity of Pseudomonas aeruginosa and Candida albicans was evaluated. Growth curves demonstrated that bacteria and fungus grew better at higher viscosity. P. aeruginosa in viscous solutions were larger than the planktonic cells. C. albicans was reduced in size at higher viscosity. P. aeruginosa and C. albicans grown in viscous solutions demonstrated decreased susceptibility to antibiotics similar to the biofilm organisms, indicating that viscosity of the environment is a possible mechanism for biofilm phenotypic expression.