Biofilms are communities of microorganisms that can grow on many different surfaces. Microorganisms that form biofilms include bacteria, fungi, and protists (Visyasagar, 2016). In contact lens wear, these free-floating microbes can easily adhere to the inside of a lens case and begin to secrete proteins that create a protective outer coating (Bispo et al, 2015). Biofilms are matrix-like structures that can attach to both living and non-living surfaces and have been found on other medical devices such as prosthetic heart valves and coronary stents (Bispo et al, 2015). Another example of a biofilm is dental plaque, a slimy buildup of bacteria that forms on teeth surfaces (Visyasagar, 2016).

Microbial adhesion and biofilm formation on contact lens surfaces are associated with serious eye infections such as microbial keratitis. Although microbial keratitis is a rare complication of contact lens wear, it is one of the primary causes of blindness (Evans and Fleiszig, 2013). The most common bacteria in contact lens-related eye infections are multi-drug-resistant Pseudomonas aeruginosa or Staphylococcus aureus (especially methicillin-resistant S. aureus [MRSA]); Candida albicans is the most common yeast in contact lens-related eye infections (Dosler et al, 2020).

Biofilms on Contact Lenses

In a recent study, contact lens biofilm models were designed to mimic differences in specific conditions (Dosler et al, 2020). Anti-biofilm activities of commercially available contact lens multipurpose solutions (MPSs) and antibiotic eye drops against mature biofilms of S. aureus, P. aeruginosa, and C. albicans were evaluated. Both standard and clinical strains were determined by the time killing curve (TKC) method at six, 24, and 48 hours. Optimal biofilms developed in a mixture of bovine serum albumin (20% v/v) and lysozyme (2 g/L) diluted in phosphate-buffered saline (PBS) at 37º C for 24 hours.

Different types of contact lenses were compared under the same conditions. The strongest biofilms, according to cell density, formed on PureVision (Bausch + Lomb [B+L]) contact lenses, then Softlens 38 [B+L] contact lenses, followed by Acuvue 2 (Johnson & Johnson Vision) and Softlens Toric (B+L)contact lenses, which were similar. Of interest, there was a significant increase in the density of biofilms on used or worn contact lenses when compared with new lenses.

The most active MPS against both P. aeruginosa and S. aureus biofilms at 24 hours was Opti-Free (Alcon), then Biotrue and Renu (both B+L). Additionally, the most active MPS against C. albicans was Renu, followed by Opti-Free and Biotrue at 48 hours. Opti-Free was the only MPS that demonstrated 3 log bactericidal/fungicidal activity against S. aureus and P. aeruginosa biofilms during a six-hour contact time. According to the International Organization for Standardization (ISO) 14729 guidelines for MPSs, “the solution should induce a 3 log reduction of reference bacterial or fungal strains,” (ISO, 2001). All antibiotic eye drops that were studied were effective against S. aureus and P. aeruginosa biofilms on contact lenses at six hours and at 24 hours either directly or as 1/10 concentrations.

Although antibiotic drops are effective against biofilm formation, this is not a practical option for daily contact lens use. It is optimal to prevent contact lens-related eye infections with effective disinfection of contact lenses using multipurpose or hydrogen peroxide solutions. According to this study, the effectiveness of anti-biofilm activities of MPSs depends on their chemical ingredients and contact times, the type of infectious agent, and the specific type and usage time of contact lenses. This information is valuable when educating patients about the importance of proper contact lens disinfection. CLS

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