Chemical inactivation of microorganisms on rigid gas permeable contact lenses

The efficiency of four contact lens disinfectant formulations was tested against three types of bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, and Serratia marcescens) and one fungus (Aspergillus niger). The bacteria were tested both as free suspensions and after attachment on surfaces of rigid gas permeable contact lenses (RGPCL). The disinfection data were used to calculate the death rates and decimal reduction times for the test organisms. P. aeruginosa was the most sensitive and A. niger was the most resistant organism to the disinfectants. Scanning electron micrographs showed that P. aeruginosa occurred mostly as single cells, with little extracellular material, on the lens surface. In contrast, S. marcescens produced copious amounts of capsular material layered on the lens surface, promoting cell aggregation. Transmission electron micrographs revealed that bacterial cells were physically separated from the lens surface by a space barricaded with capsular material.