Different contact lens case treatment methods for the elimination of pathogen biofilms associated with contact lens related microbial keratitis

Objective To investigate the biofilm-forming abilities of pathogens associated with contact lens related microbial keratitis and to compare the efficacies of different treatments in eliminating biofilms in contact lens cases (CLCs). Methods Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans biolm formation in polypropylene CLCs was examined by using a static biofilm formation model, which was incubated at 37 ℃ for 24 hours.According to the CLC treatment methods, the experimental groups were divided into a control group, a room temperature air-drying group, a contact lens care solution soaking group, a heat-drying group and a soaking-heating group.A pathogen colony counting-based serial dilution micro-counting method was applied to evaluate the biofilm elimination efficacies and pathogen killing rates of treatments. Results All four tested strains formed biofilms on the inner walls of the CLC, and the biomasses of S. aureus, P. aeruginosa, E.coli and C. albicans biofilm were (10.78±2.12), (9.19±0.57), (8.03±0.30), and (7.50±0.07)lg CFU/ml, respectively.The S. aureus biofilm biomass was significantly higher than those of the other strains (P<0.05). The biofilm biomasses of all the tested strains in the heat-drying and the soaking-heating groups were significantly lower than those in the control group (all at P<0.05); and the biofilm biomasses of S. aureus and E. coli in the soaking group were significantly lower than that in the control group (all at P<0.05). The heat-drying treatment resulted in a killing rate of (51.76±16.75)% for S. aureus, (68.63±4.43)% for P. aeruginosa, (83.51±13.97)% for E. coli, and (97.13±5.19)% for C. albicans, respectively (F=31.806, P<0.001). Significant differences were observed between the killing rates for each bacterium (all at P<0.05). The E. coli and C. albicans killing rates of the soak-heating treatment were (100.00±0.00) % and (97.79±7.67)%, respectively, and were significantly higher than (81.13±14.86)% of S. aureus and (74.22±11.91)% of P. aeruginosa (all at P<0.05). Conclusions Heating alone or combined with the use of contact lens care solution treatment can improve the pathogen killing rates and effectively eliminate the bacterial and fungal contaminations in CLCs. Key words: Microbial keratitis; Contact lens cases; Biofilm; Heating