Relation of cholesterol-stimulated Staphylococcus aureus growth to chronic blepharitis.

PURPOSE Many types of chronic blepharitis have been believed to be primarily microbial in origin; however, it was proposed that differences and changes in lipid composition of meibomian secretion may be the initiating factor in some of these. It was recently reported that there are two subgroups of normals, those whose meibomian secretions contain high levels of cholesterol esters and those whose secretions contain very low levels of these esters. Thus, these subgroups of normals were defined on the basis of detailed lipid analyses of meibomian secretions from individuals showing no clinical signs of chronic blepharitis. All secretions from patients in the various disease groups contain high levels of these esters. Based on previous observations that in some chronic blepharitis disease groups certain Staphylococcus species were capable of hydrolyzing cholesterol esters, the authors tested the hypothesis that the resulting cholesterol might affect growth of Staphylococcus aureus. METHODS Staphylococcus aureus growth stimulation in Mueller-Hinton broth by cholesterol was determined by colony forming units. Growth stimulation by cholesterol and other additives was also determined by the optical density 650 nm method. Statistical analyses included analysis of variance and the Student's t test. RESULTS Cholesterol stimulated Staphylococcus aureus growth was significant during the first 24 hr period (20% increase at 25 microM cholesterol, P < 0.02), and for the total 48 hr period (40% increase at 400 microM cholesterol, P < 0.005) when compared to the respective control. Growth stimulation, determined by OD at 650 nm, in the presence of cholesterol was significantly greater (P < 0.02) than that in the presence of either sitosterol or cholestanol when the sterol concentration was 190 microM. CONCLUSION These results suggest that the presence and hydrolysis of cholesterol esters of meibomian secretions may contribute to the proliferation of Staphylococcus spp, especially Staphylococcus aureus, observed in some chronic blepharitis disease groups.