More than 125 million people wear
contact lenses worldwide, and
contact lens use is the single greatest risk factor for developing microbial
keratitis. We tested the antibacterial activity of multipurpose
contact lens solutions and their individual component preservatives against the two most common pathogens causing bacterial
keratitis, Pseudomonas aeruginosa and Staphylococcus aureus The in vitro antibacterial activity of five multipurpose
contact lens solutions (Opti-Free GP, Boston Simplus, Boston Advance, Menicare GP, and Lobob) was assayed by the standard broth dilution method. Synergy between the preservative components found in the top performing solutions was assayed using checkerboard and time-kill assays. The ISO 14729 criteria and the standard broth dilution method were used to define an optimized
contact lens solution formulation against a clinical panel of
drug-susceptible and
drug-resistant P. aeruginosa and S. aureus strains. Preservatives with the
biguanide function group,
chlorhexidine and
polyaminopropylbiguanide (
PAPB), had the best antistaphylococcal activity, while
EDTA was the best antipseudomonal preservative. The combination of
chlorhexidine and
EDTA had excellent synergy against P. aeruginosa A
solution formulation containing
chlorhexidine (30 ppm),
PAPB (5 ppm), and
EDTA (5,000 ppm) had three to seven times more antipseudomonal activity than anything available to consumers today. A multipurpose
contact lens solution containing a combination of
chlorhexidine,
PAPB, and
EDTA could help to reduce the incidence of microbial
keratitis for
contact lens users worldwide.