Contagious equine metritis: isolation and characterization of the etiologic agent.

The study involves a comprehensive observation and characterization of the bacteria causing contagious equine metritis (CEM) in horses by cultivating specimens from infected mares on various agar plates. The results showed that the CEM bacteria form colonies under specific conditions, and their growth, observable characteristics, and susceptibility to different environmental factors vary.

Methodology and Observation

• Specimens from various parts of infected pony mares such as the uterus, cervix and clitoris were used in the study and were developed on agar plates.
• The colonies of CEM bacteria started to become visible after 2 days of incubation under carbon dioxide on two types of agar plates named Eugon chocolate agar and Eugon blood agar plates.
• The size of the colonies observed varied from 0.2 mm to 1 mm after 2 days, which further increased to 0.3 mm to 2.0 mm by the 4th day.
• The colonies on the Eugon chocolate agar plates appeared to be shiny, brown, round, and convex between the 2nd and 4th days. They also exhibited a gliding movement when nudged with a loop.

Growth on Tryptose Blood Agar Base (TrCA or TrBA)

• The colonies grown on tryptose blood agar base (either TrCA or TrBA) measured between 0.2 to 0.3 mm on the 4th day.
• It was noted that due to their smaller size when developed on TrCA or TrBA, the colonies of CEM bacteria were easily distinguished from other contaminants, which were in larger numbers.

Properties and Requirements of the CEM Bacteria

• The research also identified certain properties and requirements of the CEM bacteria.
• One such observation was that the bacteria required hemin (a component of hemoglobin) for its growth.
• Additionally, it gelled (solidified) in water, and its growth on blood agar plates led to a delayed hemolysis (breaking down of red blood cells).
• The bacteria were found to be extremely susceptible to acidic conditions in the pH range of 3 to 4.5, signifying low acid resistance of these bacteria.

Variability of Bacterial Growth on Different Products

• It is noteworthy that the growth of the CEM bacterium exhibited a distinct difference when cultured on primary isolation media obtained from two different commercial sources.
• This suggests that the commercial source of isolation media can influence the growth and observable characteristics of CEM bacteria, emphasizing the need for standardization and quality control in the production of such isolation media.