Antimicrobial and thermostabilizing properties of a novel surfactant on different bacterial species

Formulations containing the amphipol, poly (maleic anhydride-alt-1-octadecene) substituted with 3-(dimethylamino)propylamine (PMAL), stabilized live microbes in solid films at room temperature for years, during which, no microbial growth was visually detected. This led to the hypothesis that PMAL may be responsible for this effect. Assays recommended by the Clinical Laboratory Standards Institute (CLSI) and the American Society for Testing and Materials (ASTM) for antimicrobial compounds were performed with three different bacterial strains used in the United States Pharmacopeia < 51 > Antimicrobial Effectiveness Test. The minimum inhibitory concentration (MIC50) of PMAL was 15% while the MIC90 against S. aureus was 35% and E. coli and P. aeruginosa, 30% w/v. Solution pH did not significantly impact the ability of the amphipol to inhibit microbial growth (p > 0.05). Live E. coli and P. aeruginosa were reduced by ~30% after one hour exposure to 10% PMAL in saline. Scanning electron microscopy revealed membrane disruption and blebbing. P. aeruginosa was most impacted by the film forming process with 29.95 ± 4.6% lost in films without PMAL (p < 0.001). The amphipol did not significantly reduce the number of live bacteria further when stored at 20 °C for 6 weeks. Live E. coli was reduced by 22.2 ± 2.5% by 30% PMAL with bacterium found on the outer film surface. Further changes in viability were not detected during storage at 20 °C. Gram-negative bacteria were more sensitive to PMAL than gram-positive bacteria. This property may contribute to initial loss in viability during film preparation.