Efficacy of standard disinfectant test methods for contact lens-care solutions

Two disinfection systems based on hydrogen peroxide (0.5, 1.5 and 3%) and chlorhexidine gluconate (0.004%) were challenged in suspension tests using a modification of a standard method, with inocula containing 106 or 108 cfu/ml of the standard organisms Serratia marcescens, Pseudomonas aeruginosa and Staphylococcus warneri. The effect of an organic load on the shapes of microbial inactivation curves was also investigated. Although there were rapid declines in viability of 1–2 log units (cfu/ml) within the first minute of challenge in all cases, declines in viability subsequently levelled out rapidly, and with hydrogen peroxide viable counts increased slightly thereafter. These increases are unexplained, but may in part be attributable to disruption of cell clumps during challenge.