Study of the hormetic effect of disinfectants chlorhexidine, povidone iodine and benzalkonium chloride

Abstract

The study of the dose–response relationship of disinfectants is of great importance in treating infection, the objective being to use concentrations above the minimal bactericidal concentration (MBC). Below these concentrations, the bacteriostatic or bactericidal effect may be insufficient. Moreover, at low concentrations, a hormetic effect may be observed, producing a stimulation of growth instead of inhibitory action. Hormesis is not well known in the context of antimicrobial substances. This study investigates the possible existence of a hormetic effect in three commonly used antiseptics—chlorhexidine digluconate, povidone iodine and benzalkonium chloride—on strains of reference of Staphylococcus aureus and Pseudomonas aeruginosa. Growth curves were determined for different concentrations of the disinfectants. The variables studied—concentration of disinfectant, instantaneous growth rate and number of generations—were analysed using linear, quadratic and cubic models to adjust for the variables. The three disinfectants tested show a significant hormetic effect with P. aeruginosa and a less significant effect with S. aureus. These findings point to a dose–response effect that is not linear at low concentrations, while hormetic effects observed at some low concentrations result in greater bacterial growth. In infected wounds, materials or surfaces where microorganisms may occupy zones of difficult access for a disinfectant, the hormetic effect may have important consequences.