Biocides incorporated into plasticized polyvinylchloride reduce adhesion of Pseudomonas fluorescens BL146 and substratum hydrophobicity

A quantitative adhesion assay was developed to monitor attachment of Pseudomonas fluorescens BL146 to discs of plasticized polyvinylchloride (pPVC) with and without incorporated biocides. Adherent cells were quantified by radiolabelling with DL-4,5-³H]leucine. Adhesion reached a maximum after 6 h incubation at an initial cell concentration of 5 x 10⁷ cells ml^-1. The adhesion assay was used to compare bacterial attachment to pPVC containing the biocides 10,10-oxybisphenoxyarsine (OBPA), 2- n -octyl-4-isothiazolin-3-one (OIT), 2,3,5,6-tetrachloro-4-(methylsulphonyl)pyridine (TCMP) and N -trichloromethylthiophthalimide (NCMP) at 0, 250, 750 and 2250 ppm. All four biocides reduced adhesion with increasing concentration, with statistically significant reductions in adhesion (< 53%) occurring with OBPA, OIT and TCMP at 2250 ppm. Significant reductions in adhesion to pPVC containing OBPA were found whether adhering cells were viable or non-viable. The hydrophobicity of the pPVC surfaces was quantified by the measurement of water contact angles using the Wilhelmy plate technique. A trend of reduced hydrophobicity was observed with increasing biocide concentration. Incorporation of all four biocides at 2250 ppm caused statistically significant reductions in contact angle from 104.7° to a minimum of 93.5°. Incorporation of biocides into pPVC therefore concurrently reduces both bacterial adhesion and surface hydrophobicity.