Heating as well as cleaning contact lens cases kills bacteria best

Aug 24 2012

By Sarah Guy, medwireNews Reporter

Heating contact lens cases to a temperature of 60°C while disinfecting with a multipurpose disinfecting solution (MPDS) could improve case hygiene by killing biofilms created by bacteria, report Australian researchers.

A team from the University of New South Wales in Sydney reports that following this protocol, and leaving the case to dry with the caps closed, resulted in a total kill of biofilms produced by the commonly occurring ocular pathogens Pseudomonas aeruginosa and Staphylococcus aureus.

Indeed, these results were superior to those achieved after drying cases at 14°C, representing an ambient temperature, or incubating the cases in phosphate buffered saline (PBS) at 60°C, show the study findings, published in Eye and Contact Lens.

"There is a need to improve the performance of disinfecting solutions and/or hygiene systems to reduce the contamination of lens cases during normal use and may lead to reductions in the rates of microbially driven adverse events," say the authors.

"There is a discrepancy in the advice given to contact lens wearers about how to care for their lens cases," they add.

Therefore Brian Willcox and colleagues investigated heating as a method of disinfection, after intentionally culturing P. aeruginosa and S. aureus to a degree that viable cells of these bacteria adhered to contact lens cases and formed a biofilm - a "community" of bacteria that form a protective barrier.

A temperature of 60°C for 3 hours was the optimum to reduce the number of overall viable bacterial cells compared with 14°C and 45°C, resulting in respective bacterial counts of 5.26 versus 6.29 and 5.79 CFU/mL, respectively.

Both types of bacterial biofilm were more significantly reduced if caps were closed during warming, note Willcox et al.

Incubating the lens cases at 60°C in the presence of MPDS resulted in a total kill of the biofilm of both bacteria, they found, which was a significantly improved result compared with disinfecting using MPDS at ambient temperature, or incubation in PBS at 60°C.

Specifically, the respective numbers of bacteria per CFU/mL per case after MPDS at ambient temperatures and the number after PBS at 60°C were 3.80 and 0.92 for P. aeruginosa, and 2.44 and 4.73 for S. aureus.

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