In vitro bactericidal efficacy of equine polymorphonuclear leukocytes against Corynebacterium equi.

The research explores the extent to which immune cells in adult horses, called polymorphonuclear leukocytes, can successfully destroy harmful bacteria Corynebacterium equi and Staphylococcus aureus. It concludes that these immune cells efficiently neutralize these bacteria, indicating that potential failures of this process are unlikely to significantly contribute to the development of C. equi pneumonia in horses.

Research Methodology

• The researchers collected polymorphonuclear leukocytes, a type of white blood cell, from the blood of adult horses. This was achieved using a two-step Percoll gradient process, a common method for white blood cell isolation.
• The team then tested these equine leukocytes for their capability to kill bacteria, specifically focusing on Corynebacterium equi. The bacterium Staphylococcus aureus was also included as a control group, given previous research has confirmed the efficacy of equine neutrophils against it.
• The bacterial uptake was gauged after a 15-minute incubation period of the neutrophils and bacteria in the presence of normal horse serum. This allowed the researchers to evaluate how quickly and efficiently the immune cells were reacting to the bacteria.

Findings of the Research

• The study found that the neutrophils in horses effectively consumed and killed both Corynebacterium equi and Staphylococcus aureus.
• While the proportion of uptake for Staphylococcus aureus (95% +/- 3%) was slightly higher than that of Corynebacterium equi (85% +/- 6%), the overall killing efficacy of the bacteria was equivalent in both cases.
• Over the course of a three-hour incubation period, more than 90% of the bacteria that were either ingested or attached to the neutrophils were destroyed.

Implication of the Findings

With an average of 96 +/- 2% of Corynebacterium equi and 91 +/- 8% of Staphylococcus aureus killed during the three-hour incubation, the results emphasize the substantial bactericidal efficacy of equine neutrophils. Therefore, neutrophil’s inability to kill bacteria has a low probability of playing a significant role in the development of Corynebacterium equi pneumonia in horses. This offers valuable insight for equine veterinary practice and may contribute to a more nuanced understanding of infection resistance mechanisms in horses.