Genetic basis of resistance to quaternary ammonium compounds – the qac genes and their role: a review

Although the qac genes are named after one of their main substrates (i.e., quaternary ammonium compounds), these genes also code for resistance to a broad spectrum of other cationic compounds such as intercalating dyes, diamidines and biguanides. The various Qac proteins are involved in relatively low specific effluxbased multidrug pumps and belong to a family of small multidrug resistance proteins. Even though the practical significance of qac-mediated resistance lies mainly in resistance to antiseptics, contradictory findings on this issue are still reported. Therefore, the aim of this review is to summarise the current knowledge on qac-mediated resistance with special emphasis on resistance to antiseptics and its relevance for practice.