Phagocytosis and intracellular killing of the contagious equine metritis organism by equine neutrophils in genital secretions.

This study provides insights into the interactions of equine neutrophils with contagious equine metriti organisms (CEMO) and Escherichia coli in varying conditions, and how this impacts the bacterial population and the roles of different equine genital secretions in these processes.

Objective of the study

• The research investigates how equine neutrophils interact, through phagocytosis and intracellular killing, with two types of bacteria – CEMO and E. coli. The process is measured under several conditions, including in seminal plasma, uterine flushings, and Hank’s balanced salt solution (HBSS). The aim was to understand the role of these neutrophils and secretions in controlling these bacterial populations.

Methods and Procedures

• To carry out this research, the study combined equine neutrophils with the two strains of bacteria in the aforementioned types of liquids.
• Across various time periods, they measured phagocytosis (the process where cells engulf bacteria to destroy them) and intracellular killing (where cells kill bacteria within them).
• The methods used to estimate these processes included bacterial cultures, as well as light and electron microscopy.

Findings

• They found that with lysed neutrophils (neutrophils that have broken down), the number of colony-forming units of both CEMO and E. coli increased in seminal plasma and uterine flushings. However, in HBSS, the number of CEMO decreased.
• Moreover, the numbers of CEMO increased more in the presence of seminal plasma than in other media. In all the given media, 29% to 32% of the CEMO were phagocytized by 120 minutes.
• Interestingly, at all times and in all types of media, more E. coli than CEMO were found associated with neutrophils.
• By 210 minutes incubation in uterine flushings, seminal plasma, and HBSS, 60% to 75% of the intracellular CEMO were killed. In the case of intracellular E. coli in the various media, a higher amount of 85% to 90% was killed within the same time frame.

Conclusion

• The study concluded that CEMO behaves like an extracellular pathogenic bacterium, which could imply that it poses a danger outside the cell. Also, the immunoglobulins (antibodies) found in the equine seminal plasma and uterine flushings did not appear to enhance their phagocytosis or intracellular killing of CEMO, in uninfected horses.