Enzyme-linked immunosorbent assay for the detection of antibodies to nutritionally variant streptococci in patients with endocarditis.

The viridans streptococci are responsible for 50%-55% of microbial endocarditis. Among these varied species, the nutritionally variant streptococci (NVS) have recently been associated with culture-negative endocarditis and are responsible for 5%-10% of all streptococcal endocarditis. The isolation and identification of these bacteria has been hampered by the extremely fastidious nature of their growth requirements as well as by their slow growth rate. In addition, their antibiotic sensitivity varies greatly, a characteristic leading to a higher rate of morbidity and mortality than is found in patients with non-NVS endocarditis. For these reasons sera from patients with NVS endocarditis were examined for antibodies to the NVS serotype I antigen by using an enzyme-linked immunosorbent assay. Seventy-four percent of patients with NVS endocarditis had elevated titers to this antigen. None of the sera from controls and only 6.7% of the sera from patients with non-NVS streptococcal endocarditis showed increased titers. These results indicate that antibody to the NVS serotype I antigen can serve as a marker for NVS endocarditis.