Beta-hemolytic Streptococcus equi subsp. zooepidemicus (BHS) is the most frequently isolated pathogen in the uterus of mares. However, in a large fraction (>50%) of subfertile mares there is no obvious reason identified. We recently demonstrated that BHS have the ability to reside deep in endometrium and may also gain intracellular access. The ability to escape and hide from the immune system allows BHS to cause long lasting, hardly detectable infections. In addition to this, we have shown that BHS are able to enter a dormant state where the bacteria can slow down their metabolism. Most antibiotics inhibit bacterial growth by disrupting the microbial metabolism which makes the dormant bacteria highly tolerant to antibiotics.