Susceptibility of Haemophilus equigenitalis, the causal agent of contagious equine metritis, to 31 antimicrobial agents.

This research looks into the effectiveness of 31 different antimicrobial agents against Haemophilus equigenitalis, a bacteria that causes contagious equine metritis in horses. The researchers found that 26 of the tested agents were effective against the bacteria, with certain ones showing greater activity.

Significance of the Research

• The bacteria Haemophilus equigenitalis causes contagious equine metritis, a highly infectious disease in horses that affects reproductive health.
• Understanding the effectiveness of different antimicrobial agents against this bacteria is vital for developing effective treatments and controlling the spread of the disease.

Methodology

• The researchers used the agar dilution method to determine the minimal inhibitory concentrations (MIC). This process establishes the lowest concentration of an antimicrobial agent that prevents bacterial growth.
• They tested 31 antimicrobial agents on 99 isolates of Haemophilus equigenitalis.

Results

• The bacteria responded well to 26 out of the 31 antimicrobial agents tested. This means the MIC for these agents was less than 3.13 micrograms/ml for over 90% of the isolates.
• Out of the 26 effective agents, four macrolides (erythromycin, oleandomycin, kitasamycin, and tylosin), three tetracyclines (tetracycline, chlortetracycline, and oxytetracycline), one peptide (colistin), one penicillin (ampicillin), and one pleuromutilin (tiamulin) emerged as particularly potent. For these, the MIC was below 0.39 micrograms/ml for more than 90% of the isolates.
• Conversely, more than 90% of the isolates were resistant to streptomycin, with their growth not inhibited even by 800 micrograms/ml of the agent.

Implications

• This research provides valuable insights into the potential treatments for equine metritis. Knowing which antimicrobial agents Haemophilus equigenitalis is most susceptible to can help veterinarians recommend the most effective course of treatment.
• Equally, understanding which agents the bacteria is resistant to is critical in avoiding ineffective treatments that could potentially lead to further resistance.