This study has demonstrated for the first time antimicrobial activity of melimine-coated contact lenses against
Acanthamoeba , fungi, and antibiotic resistant strains of
P. aeruginosa and
S. aureus . This extends our previous data, which demonstrated activity against one additional strain each of
S. aureus (CK5) and
P. aeruginosa (ATCC 15442) as well as a strain of
Streptococcus pneumoniae (Spneu 10).
38 Our results showed a significant reduction in the numbers of viable bacteria adherent to melimine-coated contact lenses. There were also significant reductions in the numbers of dead
P. aeruginosa adherent to melimine lenses. On the other hand, there was an increase in the level of dead (red stained) adherent
S. aureus . This difference may be due to the nutritious disparity in the media used in the bacterial assays or to the known differences in activity of melimine in solution on these two types of bacteria.
42 Any remaining dead cells on melimine-coated contact lenses are unlikely to be associated with contact lens related inflammatory events as our previous studies confirmed that melimine-coated lenses had the capacity to reduce inflammatory events like CLARE and CLPU in animal models
37 and live
S. aureus were required to produce a CLPU responses in the animal model.
12 A previous study
37 found that the total count of bacteria did not differ between control and melimine-coated lenses, but this disparity might be either the consequence of the higher concentration of melimine present in etafilcon A lenses (152 μg lens
−1) compared with the silicone hydrogel lenses (44 μg lens
−1), or due to difference in polymer characteristics of the underlying lens materials used. Moreover, the current study extends our previous finding that melimine in solution retained activity when autoclaved,
38 to show that melimine bound to a surface also retains antimicrobial activity after autoclaving. Because of highly cationic nature of melimine it is very unlikely to form a densely packed layer that interferes with oxygen permeability. However, further investigations might be indicated to evaluate any change in oxygen permeability especially with silicone hydrogel contact lenses. The current study demonstrated that covalently attaching 152 μg melimine on etafilcon A lenses did not alter lens parameters and the surface was not cytotoxic to fibroblasts. The latter finding re-enforces the previously published nonhemolytic activity of melimine in solution.
38