Plasticizers increase adhesion of the deteriogenic fungus Aureobasidium pullulans to polyvinyl chloride

Abstract

Initial adhesion of fungi to plasticized polyvinyl chloride (pPVC) may determine subsequent colonization and biodeterioration processes. The deteriogenic fungus Aureobasidium pullulans was used to investigate the physicochemical nature of adhesion to both unplasticized PVC (uPVC) and pPVC containing the plasticizers dioctyl phthalate (DOP) and dioctyl adipate (DOA). A quantitative adhesion assay using image analysis identified fundamental differences in the mechanism of adhesion of A. pullulans blastospores to these substrata. Adhesion to pPVC was greater than that to uPVC by a maximum of 280% after a 4-h incubation with 10(8) blastospores ml(-1). That plasticizers enhance adhesion to PVC was confirmed by incorporating a dispersion of both DOA and DOP into the blastospore suspension. Adhesion to uPVC was increased by up to 308% in the presence of the dispersed plasticizers. Hydrophobic interactions were found to dominate adhesion to uPVC because (i) a strong positive correlation was observed between substratum hydrophobicity (measured by using a dynamic contact angle analyzer) and adhesion to a range of unplasticized polymers including uPVC, and (ii) neither the pH nor the electrolyte concentration of the suspension buffer, both of which influence electrostatic interactions, affected adhesion to uPVC. In contrast, adhesion to pPVC is principally controlled by electrostatic interactions. Enhanced adhesion to pPVC occurred despite a relative reduction of 13 degrees in the water contact angle of pPVC compared to that of uPVC. Furthermore, adhesion to pPVC was strongly dependent on both the pH and electrolyte concentration of the suspension medium, reaching maximum levels at pH 8 and with an electrolyte concentration of 10 mM NaCl. Plasticization with DOP and DOA therefore increases adhesion of A. pullulans blastospores to pPVC through an interaction mediated by electrostatic forces.

FIG. 1

Time course of adhesion of A. pullulans IMI70103 blastospores to uPVC and pPVC. Error bars show ±1 standard error of the mean.

FIG. 2

Influence of blastospore concentration on adhesion of A. pullulans to uPVC and pPVC. Error bars show ±1 standard error of the mean.

FIG. 3

Influence of the plasticizers DOP and DOA both as a suspension and dissolved in PBS on adhesion of A. pullulans blastospores to uPVC. Error bars show ±1 standard error of the mean.

FIG. 4

Effect of increasing surface contact angle on adhesion of A. pullulans IMI70103 to different substrata. Therm., Thermanox (tissue culture-treated PET); PTFE, polytetrafluoroethylene; PP, polypropylene; FEP, fluoroethylene polypropylene; PE, polyethylene. Error bars show ±1 standard error of the mean.

FIG. 5

Influence of suspension buffer pH on adhesion of A. pullulans blastospores to pPVC and uPVC. Error bars show ±1 standard error of the mean.

FIG. 6

Effect of electrolyte (NaCl) concentration on adhesion of A. pullulans IMI70103 to pPVC and uPVC. Error bars show ±1 standard error of the mean.

FIG. 7

Zeta potentials of A. pullulans IMI70103 blastospores in PBS as a function of pH. Data points represent averages for duplicate zeta potential measurements. Error bars show ±1 standard deviation of the mean.

FIG. 8

LTSEM of blastospores attached to pPVC (a) and uPVC (b) discs following incubation with 10⁸ blastospores ml⁻¹ for 4 h. Discs were washed, fixed, and stained as normal for the adhesion assay. Bar, 20 μm.