Study of interaction effects of polyacrylic acid polymers (carbopol 940) on antimicrobial activity of methyl parahydroxybenzoate against some gram-negative, gram-positive bacteria and yeast.

Cosmetic or pharmaceutical formulations containing hydrophilic polymers of natural or synthetic origin, may be more exposed to successful microbial contamination because of a polymer-preservative interaction. The experimental data reported in this paper relate to the possible interference of Carbopol 940 with methyl parahydroxybenzoate. Results show that this hydrophilic polymer, widely employed in many formulations, exerts, on the contrary, an interesting synergism on microbicidal activity of the preserving agent against E. coli and P. Aeruginosa. A reduction in microbicidal activity against S. aureus and C. albicans is observed for a polymer concentration higher than that needed for anti-Gram-negative synergy.