The source of Streptococcus dysgalactiae is usally milk from a sick dairy cow, mastitis is not very contagious and occurs rarely in the herd.
Streptococcus dysgalactiae survives on the skin of the udder, in cmall cracks in the skin, but also on the mucous membrane of the vagina, on the tonsils, in the amniotic sacs during abortion, in the contaminated uterus. The bacterium has a strong affinity for the mammary gland and can adhere to the walls of the udder ducts and survive for many weeks. Streptococcus dysgalactiae infection is facilitated by a current infection of the mammary gland caused by mycoplasma.
The diesease usually occurs subclinically, but acute mastitis can also develop with severe impairment of general health.
In the photo of the PM test from a farm above we can see that the coloured bacterial colony Streptococcus dysgalactiae can be well distinguished, for example from Streptococcus uberis. Other streptococci important in mastitis are different in colour as well - see photos here in the atlas of the authors. In case of doubt, it is advantageous to perform a quick check in our collaborating laboratory (on MALDI TOF) and also test the antibiotics sensitivity immediatelly.