Susceptibility of equine bacterial isolates to antimicrobial agents.

This research study investigates the vulnerability of common bacterial pathogens found in horses to different antibiotics. Results for each antibiotic are given as effective concentrations against the bacteria.

Study Overview

This study aims to understand the susceptibility to antibiotics of a variety of bacterial pathogens commonly isolated from horses. These pathogens are regularly encountered in equine medicine and knowing their antibiotic susceptibility patterns is essential for effective treatment.

Methods

Researchers used the agar-plate dilution method, which is a standard technique to determine the minimum inhibitory concentration (MIC) of antibiotics needed to inhibit the growth of the bacteria. The lower the MIC, the more effective the antibiotic is against the bacteria.

Bacterial Isolates

The study profiles several aerobic bacterial pathogens, including both gram-positive and gram-negative strains such as:

• Corynebacterium (Rhodococcus) equi
• Corynebacterium pseudotuberculosis
• Coagulase positive Staphylococcus species
• Streptococcus equi
• Streptococcus zooepidemicus
• Actinobacillus species
• Enterobacter cloacae
• Escherichia coli
• Klebsiella pneumoniae
• Pseudomonas aeruginosa
• Salmonella species

Antibiotic Susceptibility

The researchers tested susceptibility to 14 different antibiotics, providing the in vitro susceptibility levels for each antibiotic. The lower the concentration required, the greater is the bacteria’s susceptibility to that antibiotic. The antibiotics and their effective concentrations are as follows:

• Amikacin (≤ 4.0 µg/ml)
• Ampicillin, Amoxicillin, Erythromycin, Penicillin, Tetracycline (≤ 1.0 µg/ml)
• Cefadroxil, Chloramphenicol (≤ 8.0 µg/ml)
• Gentamicin (≤ 2.0 µg/ml)
• Kanamycin (≤ 4.0 µg/ml)
• Sulfadimethoxine, Sulfadiazine (≤ 10.0 µg/ml)
• Ormetoprim/Sulfadimethoxine, Trimethoprim/Sulfadiazine (≤ 0.5/9.5 µg/ml)

The study provides detailed antimicrobial resistance data valuable for treating equine diseases caused by these pathogens. It helps veterinarians prescribe more effective antibiotics for treating infections in horses.