The effect of thenatural mix of polyphenols and catechin on the mat formation was not consistent for all the strain stested, as some increased mat formation with polyphenol mix and reduced with catechin. Addi-tionally, not all the strains tested in all the nutrition conditions in pres-ence of the mix of polyphenols exhibited a decrease in the area colony,as expected considering the polyphenolic composition of the dried grape skin water extract used to prepar emedia. It may be that the strain differences can be due to various polyphenolic compound sacting syner-gistically or antagonistically.