Resistance fuelling contact lens infections

A study published in the January issue of Antimicrobial Agents & Chemotherapy, has found that the high proportion of corneal infections linked to contact lens solutions are fuelled and made resistant to treatment by the formation of a highly resistant structure of microbial cells held together with a glue-like matrix material, called biofilms.

Fungal keratitis is commonly caused by Fusarium species and less commonly by Candida species. Recent outbreaks of Fusarium keratitis were associated with contact lens wear, specifically ReNu with MoistureLoc contact lens care solution (Bausch & Lomb) and biofilm formation on contact lenses or lens cases were proposed to play a role in this outbreak.

In response to this, Mahmoud Ghannoum and colleagues from the Center for Medical Mycology, University Hospitals Case Medical Center, Cleveland, USA developed an in vitro model for contact lens-associated fungal biofilm.

In their study, the research team developed and characterized in vitro models of biofilm formation on various soft contact lenses using three species of Fusarium and Candida albicans (C. albicans). The contact lenses tested were etafilcon A, galyfilcon A, lotrafilcon A, balafilcon A, alphafilcon A, and polymacon.

The results showed that clinical isolates of Fusarium and C. albicans formed biofilms on all types of lenses tested and that the biofilm architecture varied with the lens type. Moreover, differences in hyphal content and architecture were found between the biofilms formed by these fungi. It was also discovered that two recently isolated keratitis-associated fusaria formed robust biofilms, while the reference ATCC 36031 strain (recommended by the International Organization for Standardization guidelines for testing of disinfectants) failed to form a biofilm. Furthermore, using the developed in vitro biofilm model, the team showed that phylogenetically diverse planktonic Fusaria and Candida were susceptible to MoistureLoc and MultiPlus. However, Fusarium biofilms exhibited reduced susceptibility against these solutions in a species- and time-dependent manner.

As a result of this study, it is advised that industry ensure their multipurpose solutions are effective against biofilms.