[Susceptibility of bacterial isolates from the equine respiratory tract to trimethoprim, sulfadoxine, sulfadimethoxine and combinations of these compounds].

The research article centers around investigating the effectiveness of certain antimicrobial drugs and their combinations on different bacterial strains commonly found in the equine respiratory tract. The study essentially recommends that using a combination of trimethoprim and sulfonamide for the initial treatment of equine respiratory tract infections can be effective.

Objective

The researchers performed an in-vitro study to assess the susceptibility of various strains of bacteria (88 in total) isolated from horses’ respiratory tracts to three specific drugs: trimethoprim, sulfadoxine, sulfadimethoxine, as well as combinations of these drugs.

Study’s Process and Findings

• The bacterial strains that were tested were primarily Streptococcus equi subsp. zooepidemicus, Streptococcus equi subsp. equi, Staphylococcus aureus, Klebsiella pneumoniae, Rhodococcus equi, Pseudomonas spp. and Escherichia coli; aside from these, few other bacteria were also examined.
• To determine an organism’s susceptibility to the aforementioned drugs, the researchers set specific minimal inhibitory concentrations (MIC) while conducting the broth microdilution technique. These are concentrations at which the growth of a bacterium is inhibited.
• The research findings showed Rhodococcus equi to be resistant to the tested antimicrobials. This was somewhat anticipated by the researchers.
• On the other hand, the bacteria that were more commonly found in clinical scenarios showed a high susceptibility to the combinations of trimethoprim and sulfadoxine or sulfadimethoxine.
• The fractional inhibitory concentration (FIC) indices, which measure the inhibitory effect of drug combinations, indicated that the combined drugs effectively hindered bacterial growth over a wide range.

Conclusions

• Based on the results of the in-vitro testing, the study recommends the use of a drug combination of trimethoprim and sulfonamide for the initial treatment of respiratory tract infections in horses. This recommendation comes from the observed susceptibility of clinically common bacterial isolates to these combinations.