CONTRIBUTION OF THE HOST TO TEST-RESULTS IN ASSAYS OF STAPHYLOCOCCUS-EPIDERMIDIS

From two human populations (one pediatric and one adult), clinically d iagnosed with Staphylococcus epidermidis (S. epidermidis) sepsis of si milar severity, bacteria were isolated from pre-antibiotic blood sampl es and evaluated for virulence. The LD(50) of the bacteria in a mouse model was performed, with evaluation of animals dying acutely followin g intravenous S. epidermidis administration. More simple assays of vir ulence were also performed, including bacterial adherence to a fibrin clot and carbohydrate specific lectin binding, The eight pediatric-hos t S. epidermidis isolates required a significantly larger dose to prod uce lethality in dosed animals (LD(50)) when compared to the 20 adult- host S. epidermidis isolates. The fibrin clot assay, a test that has c orroborated bacterial virulence in endocarditis models, did not differ entiate the groups: all but one of the 28 isolates were well above the adherence seen with the ATCC control, suggesting endocarditis-produci ng potential. Glycocalyx (slime) from eight of the more virulent isola tes showed reactivity with a glucose-specific biotinylated lectin whic h was lacking in other isolates. Necropsy of mice dying at 12 hr showe d S. epidermidis strain differences in specific organ effects. Overall , this study demonstrates the utility of the LD(50) to provide a highl y sensitive quantification of bacterial virulence. Necropsy of test an imals dying acutely has showed an apparent organ tropism of some of th ese isolates which are usually considered harmless commensals. (C) 199 5 Wiley-Liss, Inc.