Nutritionally variant streptococci from corneal ulcers in horses.

Of 24 isolates of nutritionally variant streptococci recovered from equine corneal ulcers, 22 were tested for growth requirements, physiological and biochemical reactions, and susceptibility to different antimicrobial agents. Satisfactory growth was obtained by supplementing blood agar and Todd-Hewitt broth with pyridoxal hydrochloride, and all of the media for the culture and the biochemical testing were supplemented with 0.002% of this substance. Biochemical patterns of 12 of the isolates resembled those of two viridans streptococcal species, Streptococcus intermedius and Streptococcus constellatus. Patterns of 10 isolates did not resemble those of any recognized viridans species. All of the isolates were inhibited by less than or equal to 0.25 microgram of erythromycin per ml, less than or equal to 4 micrograms of chloramphenicol per ml, and less than or equal to 4 micrograms of gentamicin per ml, and all but two were inhibited by less than or equal to 0.1 microgram of penicillin per ml.