Streptococcus gordonii is a Gram-positive bacterium included among some of the initial colonizers of the periodontal environment.

The organism, along with related oral streptococci, has a high affinity for molecules in the salivary pellicle (or coating) on tooth surfaces. S. gordonii therefore can rapidly colonize clean tooth surfaces, and S. gordonii along with related organisms comprise a high percentage, up to 70%, of the bacterial biofilm that forms on clean tooth surfaces. Generally harmless in the mouth, S. gordonii can cause acute bacterial endocarditis upon gaining access systemically. S. gordonii also forms an attachment substratum for later colonizers of tooth surface and can modulate the pathogenicity of these secondary colonizers through interspecies communication mechanisms.

A right frontal hematoma revealed two mycotic aneurysms and an infective endocarditis due to Streptococcus gordonii. Motor weakness partially recovered after antibiotic therapy and angiography demonstrated complete resolution of aneurysms.

Ruptured mycotic aneurysms are poor prognosis factors in infective endocarditis. Adapted antibiotic therapy is the first-intent treatment ¹⁾.