| Summary: | Microbial keratitis, a vision-threatening infection commonly linked to contact lens use, poses a significant challenge, particularly when caused by <i>Acanthamoeba</i> species. Acanthamoeba keratitis (AK) is difficult to treat due to the organism’s ability to form resilient cysts, necessitating prolonged and complex therapeutic interventions. This study evaluated novel amidopropyl dimethylamines (APDs) and amidopropyl quaternary trimethylammoniums (APTs) for their antimicrobial efficacy against <i>Acanthamoeba castellanii</i> and <i>Acanthamoeba polyphaga</i> cysts. Minimum effective concentrations were determined, and time–kill assays assessed microbial inactivation over 24 h. The results indicated that certain APTs, particularly elaidamidopropyl trimethylammonium (EAPT) and oleamidopropyl trimethylammonium (OAPT), demonstrated superior cysticidal activity compared to the commercially used MAPD, achieving greater log reductions within 24 h (<i>p</i> < 0.0001) at a concentration of 25 µM. The enhanced efficacy of these compounds is potentially attributed to their unsaturated alkyl chains and positive charge, improving antimicrobial activity through the greater disruption of the <i>Acanthamoeba</i> cell membrane. These findings highlight the potential of APTs as alternative agents for incorporation into multipurpose lens disinfectants and AK treatment, offering improved disinfection efficacy. Further investigation is justified to optimise formulations for clinical and commercial applications.
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