In vitro susceptibility of Haemophilus equigenitalis, the causative organism of contagious equine metritis 1977, to antimicrobial agents.

This research examines the effect of various antimicrobial drugs on Haemophilus equigenitalis, a bacteria that causes contagious equine metritis in horses, and found that ampicillin and tetracycline were the most effective treatments.

Study Methodology

• The researchers collected clinical isolates of Haemophilus equigenitalis, the organism that causes contagious equine metritis, a sexually transmitted disease in horses.
• These isolates were then subjected to different antimicrobial agents using two methods: a disk diffusion test and the World Health Organization-International Collaborative Study agar dilution procedure.
• The disk diffusion test involves distributing the bacteria on an agar plate, placing disks soaked with different antibiotics on the surface of the plate, and measuring the area where bacterial growth is inhibited.
• The agar dilution procedure involves inserting the bacteria into agar plates containing varying concentrations of antibiotics and monitoring their growth.

Key Findings

• The study found that all strains of the bacteria Haemophilus equigenitalis were susceptible to drugs like beta-lactam antibiotics, chloramphenicol, trimethoprim-sulfamethoxazole, nalidixic acid, nitrofurantoin (Furadantin), and bacitracin.
• These drugs proved to be effective in inhibiting the growth of the bacteria, with ampicillin and tetracycline being the most active drugs against Haemophilus equigenitalis.
• However, there were two strains that were resistant to streptomycin, another type of antibiotic. The strains were also found to be susceptible to other aminocyclitol antibiotics.
• All strains were resistant to clindamycin, lincomycin, and metronidazole, indicating that these drugs may not be effective treatments for infections caused by this bacteria.

Implications

• The study’s results provide valuable insights for veterinarians and other medical practitioners treating horses with contagious equine metritis. The findings can guide them in choosing the most effective antibiotics.
• The identification of antibiotics that are ineffective against Haemophilus equigenitalis is also significant in preventing the inappropriate use of these drugs, as overuse can lead to antibiotic resistance.
• Further research is needed to investigate the mechanism of resistance of Haemophilus equigenitalis to certain antibiotics and find ways to overcome this.