The influence of water content and ionicity on the efficacy of soft contact lens care regimens on Pseudomonas aeruginosa

Background: Contact lens care regimens appear to be prescribed based on familiarity or by matching contact lens brands rather than consideration to efficacy. Aim: This study compared the effectiveness of multipurpose and peroxide cleaning solutions on low- and high-water content ionic and non-ionic soft contact lenses, in removing Pseudomonas aeruginosa (P. aeruginosa). Setting: The laboratory work was conducted by health science students in a graduate level programme in the microbiology laboratory at a university in south-eastern South Africa. Methods: A quantitative analytical experimental design was used. Four groups (labelled I, II, III and IV) of soft contact lenses, varied ionicity and water content were inoculated with P. aeruginosa and then exposed to three solutions containing antimicrobial ingredients, polyaminopropyl biguanide (Dymed), hydrogen peroxide (H2O2) and polyquaternium-1 (Polyquad). Each group contained 14 soft contact lenses, with the exception of Group III in which eight lenses were used. Saline served as the control. After 18 h, the remaining colony-forming units were counted using visual inspection as an indicator of efficacy against P. aeruginosa. Results: The solution containing H2O2 was found to be the most effective in removing P. aeruginosa from all Food and Drug Administration (FDA) groups of contact lenses whilst Dymed was found to be comparatively ineffective for this organism. Water content and ionicity had no effect on the efficacy of the solutions. Conclusion: Practitioners should consider the efficacy of the active ingredients against microorganisms when dispensing contact lens solutions, particularly for contact lens wearers at risk for P. aeruginosa infections.