Equine Reproductive Medicine — Glossary

A dormant persister cell is a bacterial cell that has entered a metabolically inactive state as a survival strategy. In this state, the bacterium does not multiply, does not respond to antibiotics (which target active growth), and is not detectable by standard culture tests. In the mare uterus, Streptococcus equi subsp. zooepidemicus can persist in this state for months or years, causing chronic infertility despite negative swab results and antibiotic courses.

→ How bActivate reactivates persister cells

Also known as: Strep zoo, S. zooepidemicus

Streptococcus equi subsp. zooepidemicus (Strep zoo) is a beta-haemolytic gram-positive bacterium and the most common cause of uterine infection in broodmares, accounting for approximately 80% of bacterial isolates in positive endometrial cultures. In mares with chronic infertility, Strep zoo can enter a dormant persister state within the deeper endometrial glands and stratum compactum — a location unreachable by routine swab culture.

→ German study: bacterial spectrum in mare uterine health

A biofilm is a structured community of bacteria enclosed in a self-produced matrix of proteins and polysaccharides. In the equine uterus, Streptococcus zooepidemicus biofilms adhere to the endometrial surface and render the bacteria resistant to both host immune defences and antibiotic treatment. Biofilm-associated infections are a major cause of chronic, recurrent endometritis in problem mares that do not respond to repeated antibiotic therapy.

→ How bActivate tackles biofilm and dormant bacteria

Subclinical endometritis is uterine inflammation in the absence of clinical signs such as discharge, fever, or irregular oestrus cycles. The mare appears reproductively normal, but microscopic inflammation or low-grade infection prevents successful embryo implantation. Because the condition produces no obvious symptoms and standard swab cultures have a detection sensitivity of approximately 33%, subclinical endometritis is one of the most common causes of unexplained infertility in problem mares.

→ Guide to endometritis in mares

Also known as: barren mare, repeat breeder

A problem mare is defined as a mare that fails to conceive despite breeding to a stallion of proven fertility over three or more consecutive oestrus cycles. The term encompasses a range of underlying causes, but in clinical practice approximately 50–75% of mares open at the end of the breeding season carry a dormant Streptococcus zooepidemicus infection that standard swab culture cannot detect.

→ Addressing the challenges of problem mares

A high-risk mare is one with one or more of the following characteristics: 12 years of age or older; three or more previous foals (multiparous); a history of pregnancy loss or abortion; or a documented previous episode of endometritis. In this group, approximately 75% carry a dormant Streptococcus zooepidemicus infection that standard endometrial swab culture cannot identify. High-risk mares are the primary indication for bActivate screening.

→ When to use bActivate — risk indicators

Reactivation, in the context of equine endometritis, refers to the process of stimulating dormant persister-state bacteria in the uterus to resume active metabolic growth. bActivate achieves reactivation by instilling a bacterial growth medium directly into the uterus during early oestrus. Within 48 hours, previously undetectable Streptococcus zooepidemicus becomes culture-positive, enabling targeted antibiotic treatment. The reactivation principle was first described by Petersen and Bojesen in Veterinary Microbiology (2015).

→ Full bActivate protocol (5 steps)