Aspects of the antimicrobial mechanisms of action of a polyquaternium and an amidoamine

Objectives: Polyquad (Alcon) (polyquaternium-1, PQ-1) and Aldox (Alcon) (myristamidopropyl dimethylamine, MAPD) are two blocides that are used commercially in a contact lens disinfecting solution, namely Opti-Free Express (Alcon) multi-purpose disinfecting solution. Their potential mechanisms of action were investigated against a range of common ocular pathogens. These were Acanthamoeba castellanii(trophozoites and cysts), Aspergillus fumigatus, Candida albicans, Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus. Methods: Three aspects were investigated: the lethal effects of the biocides on the organisms, the leakage of K+ from treated cells, and the lysis of spheroplasts derived from the cells. Results: PQ-1 was found to have predominantly antibacterial activity, and induced K+ leakage from the bacteria and C. albicans. It also caused lysis of spheroplasts of S. marcescens, but not those of C. albicans. MAPD was active against all of the organisms, but showed higher activity against the fungi and amoeba. It induced K+ leakage from A. fumigatus and C. albicans, and like PQ-1, lysed the spheroplasts of S. marcescens but not C. albicans. Conclusions: The two blocides have different spectra of antimicrobial activity. PQ-1 has mainly antibacterial activity, whereas MAPD was active against all of the test organisms, particularly the fungi.