Antiphagocytic properties of uterine isolates of Streptococcus zooepidemicus and mechanisms of killing in freshly obtained blood of horses.

This research investigates how certain strains of Streptococcus zooepidemicus, a bacterium often found in horses with endometritis, resist being killed in the blood of horses. The researchers found that some bacterial strains could multiply in the blood of some horses, while in others they were killed, providing insight into the process of phagocytosis in equine uterine fluid.

Methodology and Sample

• The study tested 22 clinical strains of bacteria, largely of the Streptococcus zooepidemicus type, all of which were linked to endometritis in horses. These strains were all assessed for their ability to resist the bactericidal properties of fresh horse blood.
• The blood used for these experiments was sourced from a single horse initially and then expanded to include blood from five additional horses.
• Several test runs were carried out with each bacterial strain exposed to the blood of the five horses sequentially.

Findings

• During the initial tests that lasted three hours, eight of the bacterial strains managed to survive and grow in the horse’s blood. The rest of the strains were killed by the blood’s natural defensive mechanisms.
• Within these surviving strains, their growth potential varied when exposed to the blood from the five additional horses. Certain strains could grow in the blood of certain horses but were killed in the blood of others. It was noted that the specific horse blood responsible for killing a certain bacterial strain was different for each strain.
• It was also discovered that the killing of the bacteria required the presence of white blood cells (leukocytes), but the specificity seemed to reside in the blood plasma. The plasma itself, however, was not bactericidal.
• Heat-stable and heat-labile components in the blood plasma, which the researchers suggest could be an antibody and complement respectively, appeared to be crucial for the bactericidal action.
• Interestingly, the isolates that could grow in fresh blood lost this ability after being taken through ten passages in artificial mediums.

Implications

This study offers valuable insight into the phagocytosis of S. zooepidemicus in equine uterine fluid, a process vital for understanding and addressing endometritis in horses. Identifying the specific conditions under which certain strains survive or perish could aid in developing improved prevention or treatment strategies for this common equine disease.