A direct quantitative agar-plate based assay for analysis of Pseudomonas protegens Pf-5 degradation of polyurethane films

Abstract

A quantitative assay was developed for the direct measurement of polymer film degradation from bacterial colonies on agar plates. Small (1mm diameter) colonies of Pseudomonas protegens Pf-5 (formerly Pseudomonas fluorescens Pf-5) were used for this work. Interactions between the Pf-5 colonies and thin polyurethane (PU) coatings on ZnSe coupons were evaluated for degradation using infrared spectroscopy. Three different coatings were analyzed and were formed from 1) a colloidal, aqueous - based polyester PU (Impranil® DLN); 2) an organic solvent - based polyester PU (Irogran); and 3) an organic solvent - based polyether PU (AS-P108). Over a 24h time period at 30°C, citrate exposed Pf-5 cultures rapidly degraded Impranil coatings, consistent with analogous zone clearing assays. However, the Irogran and AS-P108 PU's, which are not directly compatible with zone clearing assays, showed no measureable degradation by the coating assay under identical conditions. These results demonstrated the capability to evaluate any variety of polymer formulation as solid films under identical biological conditions. The results also show that rapid microbial degradation of colloidal polyurethanes such as Impranil are not necessarily representative of activity towards other PU materials.