Methods: A panel of 22 IE (VGS group: mutans n=4, mitis n=14, salivarius n=3, anginosus n=1) and 16 non-IE clinical isolates (VGS group: mitis n=11, salivarius n=2, anginosus n=3) was assessed for their ability to produce neuraminidase and bind plasminogen. Neuraminidase production was quantified using the colorimetric substrate 2-O-(p-nitrophenyl)-a-D-N-acetylneuraminic acid, while evaluation of plasminogen binding was performed through quantification of its active form plasmin using the colorimetric substrate D-Val-Leu-Lys-p-nitroanilide,
Results: Neuraminidase activity was detected in clinical isolates of the mitis group, including S. oralis (n=3/4; 75%), S. mitis (n=1/2; 50%) and S. oligofermentans (n=1/1; 100%), and non-IE S. mitis (n=3/11; 27%). Although the ability to bind plasminogen was a universal characteristic of the VGS tested, they bound with different affinities. Despite this variation there was no discernable correlation between species and/or VGS groups. Furthermore, the expression of this potential pathogenic trait was also variable among IE and non-IE related isolates,
Conclusions: This study demonstrated that expression of neuraminidase is predominantly associated with species within the mitis group which correlates with the current epidemiology of streptococcal endocarditis. The ubiquitous ability of VGS to bind plasminogen indicates that all species have the potential to use host plasminogen to assist in their dissemination through embolic events.
Research funded by Glasgow Caledonian University.