Staphylococcus aureus is a leading cause of nosocomial infections. Acanthamoeba is a protozoan pathogen that is remarkably similar to macrophages, particularly in their cellular structure and phagocytosis. The interactions of methicillin-resistant S. aureus (MRSA), methicillin-sensitive S. aureus (MSSA) and S. epidermidis (SE), clinical isolates, with A. castellanii and macrophage-like cell line (ThP 1) revealed similarities in their binding/association, invasion and survival. Additionally, it was shown that bacteria survive and multiply inside A. castellanii during the encystment process as evidenced by bacterial recovery from mature cysts and EM. Using an environmental isolate of S. aureus, BHICC, and mutants lacking major autolysin gene (atl), polysaccharide intercellular adhesion gene (ica) and fibronectin binding proteins A and B (FnBPAB), this study demonstrated the ability and importance of atl gene, ica gene and FnBP AB in attachment, invasion and survival within pathogenic Acanthamoeba T4 genotype, non-pathogenic Acanthamoeba T7 genotype and ThPl macrophage-like cells. Subsequently, this study investigated the effectiveness of five disinfectants currently in use in the UK hospitals, namely, 10% actichlor, 70% ethanol, 1% virkon, 5% biocleanse and hand sanitizer, on MRSA, MSSA and SE survival within trophozoites and cysts of pathogenic A. castellanii T4 genotype and non-pathogenic A. astronyxis T7 genotype. The fmdings revealed that the multi-drug resistant intracellular MRSA withstands exposure to these disinfectants more readily than the intracellular, antibiotic-sensitive MSSA, or the avirulent SE. The next aspect studied was the effectiveness of 5-ALA mediated photodynamic therapy (PDT) on MRSA, MSSA, SE, Acanthamoeba and internalized bacteria. The results showed that 5-ALA mediated PDT reduces Acanthamoeba trophozoites and intracellular bacterial viability as compared with controls, which were maintained in the dark. Interestingly, in percentage terms, the number ofMRSA, MSSA and SE that survived within trophozoites, mirrored the percentage determined for bacteria cultured under axenic conditions.