Clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine in a Streptococcus equi subsp. zooepidemicus infection model in ponies.

The research explores the effects of a prophylactic drug, trimethoprim/sulfadiazine (TMP/SDZ), on a specific type of bacterial infection in ponies. Although the drug was able to significantly reduce the presence of bacteria, it was unable to fully remove the infection, leading to the conclusion that it may not be the best line of treatment for similar infections in horses.

Research context

• The research was conducted to assess the prophylactic administration of trimethoprim/sulfadiazine (TMP/SDZ) in a Streptococcus equi subsp. zooepidemicus infection model using ponies.
• Streptococcus equi subsp. zooepidemicus is a bacterium that can cause various infections in equines, ranging from respiratory disease to wound infections, abortion, and even meningitis.
• TMP/SDZ are antibacterial drugs commonly used in equine medicine, but their efficacy in treating this specific infection is unproven.

Approach and Methodology

• The scientists created tissue chambers in the necks of the ponies, which were then infected with Streptococcus equi subsp. zooepidemicus to create a controlled model of the disease.
• The ponies were treated with TMP/SDZ both intravenously and orally three hours prior to the bacterial inoculation. The oral treatment was repeated every 12 hours for five days.
• The TMP/SDZ concentrations in the tissue chamber fluid were tracked to ensure they were maintained at a level ten times greater than the minimum inhibitory concentration (MIC), the lowest concentration of a drug that prevents the growth of a particular bacterium.

Key Findings

• The use of TMP/SDZ treatment resulted in a significant reduction of viable bacteria in the ponies’ tissue chambers.
• However, despite the marked bacterial reduction, the treatment was not able to fully eliminate the infection, leading to abscessation (the formation of abscesses) from day 19 onwards in all six ponies.
• This proves that even when there are high concentrations of TMP/SDZ, the drug is unable to fully eradicate Streptococcus equi subsp. zooepidemicus, particularly when the infection is in a secluded site like the implanted tissue chamber.

Conclusions

• The research concludes that the use of TMP/SDZ should not be the preferred course of treatment for infections caused by Streptococcus equi subsp. zooepidemicus in secluded sites in horses, given its inability to eliminate the bacteria in the study.
• Although the drug can reduce the presence of viable bacteria significantly, its inability to eradicate the infection entirely limits its efficiency as a treatment for such conditions.