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C. Lakkis, M. Boyd; The Effect of Organic Soil on Serratia Marcescens Susceptibility to Contact Lens Disinfection . Invest. Ophthalmol. Vis. Sci. 2005;46(13):920.
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Purpose: The presence of organic material, such as tear film components, may affect the antimicrobial efficacy of some chemical contact lens disinfectants. We have shown that P. aeruginosa isolates vary in their resistance to chemical disinfectants in the presence of organic soil. S. marcescens is a common causative organism in CL–associated microbial keratitis. The aim of this study was to investigate the effect of organic soil, using an artificial tear model, on disinfection susceptibility of S. marcescens strains. Methods: Disinfection susceptibility of five S. marcescens isolates (1 lab and 4 clinical strains) was investigated with and without the addition of organic soil. The ISO 14729 organic soil (artificial tear) model was utilized; heat killed S. cereviseae in inactivated fetal bovine serum. Three disinfectants were assessed: A) preserved with polyquaternium–1 0.001% and myristamidopropyl dimethylamine 0.0005%, B) and C) preserved with polyhexamethylene biguanide (PHMB) 0.0001%. Testing was carried out in CL cases at room temperature using an initial inoculum of 106 CFU/ml. The number of bacterial survivors was determined at 4 and 6 h post–inoculation via viable counts. Results: Resistance to disinfection varied significantly between the strains for solutions A & B, with poorer efficacy observed with the addition of organic soil compared to unsoiled samples for at least one of the isolates (P<0.05). Overall, resistance to solution B was significantly greater with the addition of organic soil at both 4 and 6 h (P<0.05). Susceptibility to solution C did not vary significantly between the strains in the presence or absence of organic soil (P>0.05) and solution C was the only disinfectant to achieve log reductions of at least 3.0 for all strains under all test conditions. Conclusions: S. marcescens isolates varied in susceptibility to two out of three chemical contact lens disinfectants in the presence of organic soil, with the majority of isolates showing greater disinfection resistance when tested with organic soil. The presence of organic material, such as tear film components, during CL disinfection may increase bacterial resistance to disinfection and result in subsequent contamination of CLs and CL care systems. Further investigation of factors contributing to S. marcescens resistance is warranted.
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