Effect of pyridoxal on growth of nutritionally variant streptococci and other bacteria on sheep blood agar.

Supplementation of sheep blood agar with pyridoxal hydrochloride or pyridoxamine dihydrochloride aided recovery of nutritionally variant streptococci; however, it was found to prevent recovery of 6 of 173 (3%) primary isolates of Streptococcus pyogenes and to adversely affect laboratory recognition of other streptococci. Pyridoxal hydrochloride or pyridoxamine dihydrochloride should not be a routine supplement in all sheep blood agar.