Nutritionally variant streptococci from corneal ulcers in horses

Area of Science:

• Veterinary Microbiology
• Ophthalmology
• Bacteriology

Background:

• Equine corneal ulcers can be caused by various bacteria, including streptococci.
• Nutritionally variant streptococci (NVS) present unique culture challenges.
• Understanding NVS characteristics is crucial for effective equine eye infection treatment.

Purpose of the Study:

• To characterize nutritionally variant streptococci isolated from equine corneal ulcers.
• To determine the growth requirements, biochemical profiles, and antimicrobial susceptibility of these isolates.

Main Methods:

• Twenty-four NVS isolates were recovered from equine corneal ulcers.
• Twenty-two isolates were tested for growth requirements, physiological and biochemical reactions.
• Antimicrobial susceptibility testing was performed using various agents.

Main Results:

• Pyridoxal hydrochloride supplementation (0.002%) was essential for satisfactory growth of NVS on blood agar and Todd-Hewitt broth.
• Twelve isolates exhibited biochemical patterns similar to Streptococcus intermedius and Streptococcus constellatus.
• Ten isolates did not match any recognized viridans streptococcal species.
• All isolates were highly susceptible to erythromycin, chloramphenicol, and gentamicin.
• All but two isolates were highly susceptible to penicillin.

Conclusions:

• Nutritionally variant streptococci from equine corneal ulcers require pyridoxal for optimal growth.
• These NVS isolates show varied biochemical profiles, with some resembling known viridans streptococci.
• The isolates demonstrated significant susceptibility to key antimicrobial agents, including erythromycin and penicillin.