Growth of nutritionally variant streptococci on common laboratory and 10 commercial blood culture media

Abstract

Nutritionally variant streptococci fail to grow on routine sheep blood agar plates. Moreover, these strains are a recognized cause of culture-negative endocarditis. We tested the ability of chocolate and brucella blood agars, sheep blood agar with a staphylococcal streak, sheep blood agar with 0.001% pyridoxal, and 10 commercial blood culture media from two manufactures to grow these bacteria. Of the original 25 strains tested, 16 were recovered on chocolate agar, 21 were recovered on brucella blood agar and 21 were recovered on sheep blood agar with a staphylococcal streak. Sheep blood agar with pyridoxal grew all 22 strains tested. Supplemented peptone, thioglycolate, and thiol broths grew all strains, but brain heart infusion and three tryptic soy broths supported five or fewer strains. The addition of 5 ml of human blood improved recovery to 100% in all media except tryptic soy broths. Unless supplemented wih pyridoxal, common laboratory agars were inadequate for recovering all strains of variant streptococci upon subculture of blood culture bottles. As used clinically, the blood culture media that we studied other than tryptic soy broths should reliably grow these bacteria.