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Veterinary world2025; 18(12); 3779-3787; doi: 10.14202/vetworld.2025.3779-3787

In vitro inhibitory effects of gentamicin and ceftiofur against Trypanosoma evansi: Promising antibiotic alternatives for equine trypanosomosis in Thailand.

Abstract: infection (Surra) remains a major constraint to equine health and productivity in Thailand. The only available trypanocidal drug, diminazene aceturate (DA), has limited efficacy, poor blood-brain barrier penetration, and toxicity in horses. This study aimed to investigate the inhibitory effects of commonly used equine antibiotics, gentamicin (GMC), ceftiofur (CTF), and trimethoprim-sulfamethoxazole (TS), against (Thai strain isolated from dairy cattle number 953; TEDC 953) to identify potential therapeutic alternatives or adjuncts for equine trypanosomosis. Unassigned: An growth inhibition assay was conducted using the TEDC 953 strain cultivated in Hirumi's Modified Iscove's medium 9 (HMI-9 medium) containing 20% horse serum under controlled conditions (37°C, 5% CO, 75% humidity). Serial dilutions of DA, GMC, CTF, and TS were tested in duplicate across three independent experiments. Parasite viability was assessed after 48 h by microscopic examination, and the half-maximal effective concentration (EC) was determined using nonlinear regression analysis in GraphPad Prism 5. Unassigned: Among the three antibiotics, GMC and CTF significantly inhibited growth , whereas TS showed no inhibitory effect. The EC values were 1.25 × 10 ± 3.90 × 10 mg/mL for DA, 0.22 ± 0.08 mg/mL for GMC, and 0.08 ± 0.05 mg/mL for CTF. Parasite viability assays confirmed that GMC (5 mg/mL) and CTF (0.2 mg/mL) completely eliminated after 48 h of exposure. These findings provide the first evidence of the trypanocidal potential of GMC and CTF against the Thai strain of . Unassigned: GMC and CTF exhibited substantial inhibitory activity against under conditions, supporting their potential use as repurposed or adjunct antibiotics for trypanocidal therapy in horses. This preliminary evidence underscores the need for validation, pharmacokinetic profiling, and mechanistic studies to explore synergistic effects with conventional trypanocides such as DA.
Copyright: © Rudeekiatthamrong, et al.
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Publication Date: 2025-12-10 PubMed ID: 41716180PubMed Central: PMC12913916DOI: 10.14202/vetworld.2025.3779-3787Google Scholar: Lookup
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Summary

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Overview

  • This study evaluated the in vitro effectiveness of the antibiotics gentamicin and ceftiofur against Trypanosoma evansi, a parasite causing equine trypanosomosis (Surra) in Thailand.
  • The goal was to identify alternative or adjunct treatments to the current drug, diminazene aceturate, which has limitations in efficacy and safety for horses.

Background and Problem Statement

  • Equine trypanosomosis (Surra) is a significant disease affecting horse health and productivity in Thailand.
  • The current treatment drug, diminazene aceturate (DA), has several drawbacks:
    • Limited efficacy against the parasite.
    • Poor penetration of the drug across the blood-brain barrier.
    • Toxic side effects in horses.
  • Thus, there is a necessity to explore alternative drugs or adjunct therapies that are safer and more effective.

Objective of the Study

  • To examine the inhibitory effects of three commonly used equine antibiotics—gentamicin (GMC), ceftiofur (CTF), and trimethoprim-sulfamethoxazole (TS)—against a Thai strain of Trypanosoma evansi (TEDC 953).
  • To identify possible new treatment options or complements to existing therapy for equine trypanosomosis.

Methods

  • The Trypanosoma evansi TEDC 953 strain was cultured in vitro in Hirumi’s Modified Iscove’s medium 9 (HMI-9) supplemented with 20% horse serum.
  • Culture conditions were maintained at 37°C with 5% CO2 and 75% humidity.
  • Growth inhibition assays tested serial dilutions of DA, gentamicin, ceftiofur, and trimethoprim-sulfamethoxazole in duplicate over three independent experiments.
  • Parasite viability was microscopically assessed after 48 hours of drug exposure.
  • Half-maximal effective concentration (EC50) values were calculated using nonlinear regression analysis via GraphPad Prism 5 software.

Results

  • Gentamicin (GMC) and ceftiofur (CTF) showed significant inhibition of Trypanosoma evansi growth.
  • Trimethoprim-sulfamethoxazole (TS) did not inhibit parasite growth.
  • Calculated EC50 values were as follows:
    • Diminazene aceturate (DA): 1.25 × 10⁻² ± 3.90 × 10⁻³ mg/mL
    • Gentamicin: 0.22 ± 0.08 mg/mL
    • Ceftiofur: 0.08 ± 0.05 mg/mL
  • Parasite viability was completely eliminated by exposures to GMC at 5 mg/mL and CTF at 0.2 mg/mL after 48 hours.
  • This study provides first-time evidence demonstrating the trypanocidal potential of gentamicin and ceftiofur against the Thai strain of Trypanosoma evansi.

Conclusions and Significance

  • Gentamicin and ceftiofur possess substantial in vitro inhibitory activity against Trypanosoma evansi and may serve as promising repurposed or adjunct antibiotics for treating equine trypanosomosis.
  • The results encourage further research including:
    • In vivo validation studies to confirm efficacy and safety in horses.
    • Pharmacokinetic and pharmacodynamic profiling to optimize dosing and treatment regimens.
    • Mechanistic investigations to understand how these antibiotics inhibit the Trypanosoma parasite.
    • Exploration of potential synergistic effects when combined with traditional trypanocidal drugs such as diminazene aceturate.
  • Overall, this study opens new avenues for alternative therapeutics, addressing limitations of current Surra treatments in equine veterinary medicine in Thailand.

Cite This Article

APA
Rudeekiatthamrong A, Nguyen GT, Kamyingkird K. (2025). In vitro inhibitory effects of gentamicin and ceftiofur against Trypanosoma evansi: Promising antibiotic alternatives for equine trypanosomosis in Thailand. Vet World, 18(12), 3779-3787. https://doi.org/10.14202/vetworld.2025.3779-3787

Publication

Veterinary world
ISSN: 0972-8988
NlmUniqueID: 101504872
Country: India
Language: English
Volume: 18
Issue: 12
Pages: 3779-3787

Researcher Affiliations

Rudeekiatthamrong, Apiraya
  • Department of Parasitology, Faculty of Veterinary Medicine, Kasetsart University, Lad Yao, Chatuchak, Bangkok, Thailand.
Nguyen, Giang Thi
  • Department of Parasitology, Faculty of Veterinary Medicine, Kasetsart University, Lad Yao, Chatuchak, Bangkok, Thailand.
Kamyingkird, Ketsarin
  • Department of Parasitology, Faculty of Veterinary Medicine, Kasetsart University, Lad Yao, Chatuchak, Bangkok, Thailand.

Conflict of Interest Statement

The authors declare that they have no competing interests.

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