Mastitis Case Studies

Major Mastitis-Causing Pathogens

This resource describes the major mastitis-causing pathogens.

Streptococcus agalactiae : Strep. agalactiae is a gram positive bacterium which inhabits ducts and cisterns of the gland. It causes an inflammation which blocks the ducts, leading to decreased milk production, increased somatic cell count, and eventually to involution. It has few enzymes/toxins and is very sensitive to antibiotic treatment. Strep. agalactiae infection is associated with contagious mastitis.

Staphylococcus aureus : Staph. aureus is the number one cause of mastitis in the USA. It causes peracute, acute, chronic, and subclinical mastitis. The chronic subclinical form is the predominate form. It produces many enzymes/toxins (catalase, coagulase), it is highly invasive (produces hyaluronidase which allows it to invade tissues), is often can resist phagocytosis (it has Protein A on its surface), it resists the immune system (produces teichuronic acid), it is a facultative intracellular pathogen (an live inside phagocytic cells). Staph. aureus can survive to a limited degree in the environment. It is often isolated from mammary glands of primigravid heifers and is a major cause of mastitis in heifers. Some Staph. aureus strains have antibiotic resistance resulting from genetic mutations, and penetrance and L-forms can contribute to the problems with treatment. It forms abscesses in the tissue which may result in fibrosis. The end result is decreased milk production and increased somatic cell count. Staph. aureus infection is associated with contagious mastitis.

Staphylococcus aureus bacteria on a blood agar plate.

Mycoplasma : Mycoplasma is a pleomorphic organism (has no cell wall). It can be isolated from the respiratory and urogenital tracts. It is a mastitis epizootic. There is no treatment; must segregate or cull the cow. Mycoplasma infection is associated with contagious mastitis.

Coliforms : The organisms which cause mastitis include Esherichia coli, Klebsiella spp., Enterobacter spp., and Citrobacter spp.. They are all gram negative. They are found in the feces, in bedding, on wet dirty udders. They cause transient peracute or acute mastitis. They produce endotoxin. They often increase in numbers in warm, wet weather. Coliform infections are associated with environmental mastitis.

Esherichia coli on a blood agar plate.	Psuedomonas on a blood agar plate.
Klebsiella pneumoniae on a blood agar plate.	Klebsiella oxytoca on a blood agar plate.

Environmental Streptococcal species : These include Strep. dysgalactiae, Strep. uberis, and enterococci. They are all gram positive. They can live on the skin and in the cow's environment. Infection by these streptocaccal species are associated with environmental mastitis. They cause clinical or subclinical mastitis.

Pseudomonas spp. : These are gram negative, cause clinical or subclinical mastitis and are ubiquitous in the environment. They often are found in contaminated water/pipelines/wash hoses. The only way to get rid of them may be to throw away the pipeline or heater, etc. They may also come from contaminated teat dips or antibiotic infusion. They are resistant to antibiotics. Pseudomonas infections would be associated with environmental mastitis.

Prototheca : These are alga which live in wet soil and mud. They cause chronic mastitis resulting in decreases in milk production. Prototheca infections would be associated with environmental mastitis.

Yeasts : These may enter the gland by way of needles and syringes that are reused. This happens when there is excessive antibiotic therapy occurring. They may also be transmitted by contaminated infusions. Yeast infections would be associated with environmental mastitis.