Bacterial contamination of stock solutions in storage cases for contact lens, and the disinfectant-resistance of isolates

To investigate the bacterial contamination of preservative solutions for contact lenses, contact lens cases were swabbed and the swabs were cultured. Various bacteria were isolated from 26 of 100 samples (26.0%). By preservative solution, the bacterial presence was low (16.7%) in the 30 samples from cases using ReNu, which was the most frequently employed solution, and 27.3% in 11 samples from cases using Complete, which was the second most frequently employed solution. Of 34 strains isolated and identified, gram-negative bacilli-glucose non-fermenting bacteria were the most frequently isolated, accounting for 61.8% (21 strains); particularly, 10 isolates were Stenotrophomonas maltophilia, accounting for 29.4%. The biofilm-forming ability of these isolates was investigated by staining. The mean absorbance of the gram-negative rods was 0.369, which was about 3 times higher than that (0.107) of the Staphylococcus group, confirming marked biofilm-forming ability. In addition, the bactericidal effects of the preservative solutions on the isolates were investigated. The effect varied among the preservative solutions in the suspension experiment, but the highest disinfection rate, which was achieved by Complete, was 99.9->99.99%, showing a favorable bactericidal effect. In contrast, none of the 3 test preservative solutions showed any bactericidal effect in the adhesion experiment.