The Production of Protease Activities by Streptococcus oralis Strains Isolated from Endocarditis

Abstract

Nine Streptococcus oralis strains isolated from cases of endocarditis (n=5) and from the normal oral flora (n=4) were examined for their ability to produce a number of protease activities measured using the following 7-amido-4-methylcoumarin (-AMC) linked fluorogenic substrates: BOC-leu-ser-thr-arg-AMC, gly-pro-AMC, CBZ-lys-AMC, arg-AMC and BOC-val-pro-arg-AMC, a synthetic substrate for thrombin. The influence of glucose and porcine gastric mucin on their production was determined. The distribution of the protease activities between cell-associated and supernatant was not significantly associated with the origin of the strains. However, BOC-leuser-thr-arg-AMC and BOC-val-pro-arg-AMC hydrolysing activity was greater in the supernatant while the gly-pro-AMC, CBZ-lys-AMC and arg-AMC hydrolysing activity was more cell associated, irrespective of whether the cells were grown in minimal media supplemented with either glucose or PGM. Inclusion of increasing concentrations of glucose in media containing a constant PGM concentration (0.25 per cent w/v) resulted in significant reductions in the supernatant protease activity hydrolysing BOC-leu-ser-thr-arg-AMC and BOC-val-pro-arg-AMC while the cell-associated activity hydrolysing CBZ-lys-AMC and arg-AMC increased and the hydrolysis of gly-pro-AMC was essentially unaltered. The response of S. oralis proteolytic activities to changes in media composition, including the inclusion of a model glycoprotein, PGM, was not predictable but indicated that strains from endocarditis and from the normal oral flora were indistinguishable. The production of proteases in vivo may depend upon the level of fermentable carbohydrates in the circulation but at low concentrations elevated levels of protease activity, including a thrombin-like activity, may be found within fibrin-platelet thrombi associated with endocarditis.

Key Words:

• Streptococcus oralis
• protease
• mucin
• endocarditis