The control of environmental mastitis pathogens, such as Klebsiella spp., is a daunting task. Klebsiella is an environmental organism commonly found in manure and organic bedding. Due to the nature of these bacteria, emphasis needs to be placed on prevention of infections, rather than on treatment.

The control of environmental mastitis pathogens, such as E. coli., is a daunting task. E. coli is an environmental organism commonly found in manure and organic bedding. E. coli mastitis is typically associated with a quick onset and often severe clinical signs. Due to the nature of these bacteria, emphasis needs to be placed on prevention of infections, rather than on treatment.

Staphylococcus aureus (S. aureus) is a contagious mastitis pathogen that is extremely difficult to control by treatment alone. The spread of S. aureus can occur through milkers' hands, washcloths, teat cup liners, and flies. Successful control is gained only through prevention of new infections and culling of infected animals.

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Streptococcus dysgalactiae has the unique characteristic of being considered both a contagious and environmental pathogen. These organisms can spread from cow to cow at milking time, and are also commonly found in the cow’s environment. A successful control program includes prompt treatment of cases, the use of proper milking procedures and dry cow therapy.

The incidence of Streptococcus agalactiae mastitis in the United States has been significantly reduced in recent decades. However, some farms continue to struggle with the control of this contagious pathogen. A successful control program includes prompt treatment of cases, the use of proper milking procedures and dry cow therapy.

Mastitis cases caused by yeast and mold are typically sporadic and are usually not a significant issue in a herd. Yeast form white or cream-colored colonies that can easily be confused with coagulase-negative staphylococci. Gram staining will differentiate yeast from CNS; yeast are two to three times larger than CNS and typically exhibit budding. Mold colonies can have a fluffy texture and exhibit several different colors.

Coagulase negative staphylococci (CNS) and Staphylococcus hyicus are mastitis-causing pathogens that originate from skin flora. CNS infections are usually mild and subclinical, and result in a two- to three-fold increase in somatic cell count. Proper milking procedures including the use of efficacious post-milking teat disinfectants and milking clean, dry teats will help to reduce the number of new infections.

Corynebacterium bovis is a contagious mastitis-causing pathogen. It is mildly pathogenic, and will usually cause only a mild increase in SCC and a slight reduction in milk production. Efficacious post-milking disinfectants will dramatically reduce the infection rate from C. bovis, and dry cow therapy is very effective in eliminating C. bovis.

Enterobacter spp. are environmental mastitis-causing pathogens. The spread of Enterobacter spp. occur primarily through environmental contact, particularly when teats come in contact with manure or contaminated bedding. The primary way to prevent infection by Enterobacter spp. is by keeping cows clean and dry to decrease exposure, as well as proper teat sanitation prior to milking.

Mycoplasma spp. are a contagious mastitis-causing pathogen. Infected cows typically have mastitis in multiple quarters and exhibit a dramatic decrease in milk production. A Mycoplasma spp. mastitis outbreak can be preceded by a respiratory disease event in bovines of different ages on the farm.

Pasteurella spp. are contagious pathogens that are seldom reported as a cause of bovine mastitis. Mastitis caused by Pasteurella spp. usually appears as a thick, creamy-yellow, viscous secretion, sometimes with a foul odor. The spread of Pasteurella spp. is not fully understood, but most likely is cow to cow. Preventing teat injuries and removing infected cows are the main ways to prevent and control this pathogen. Pasteurella spp. do not respond well to antibiotic therapy and can result in death; thus, prevention is key.

Proteus spp. are uncommon environmental mastitis pathogens that have been known to cause outbreaks. Little is known about how Proteus spp. infect the mammary gland, however procedures effective in controlling coliform mastitis pathogens should apply to Proteus spp. as well. Proteus spp. typically cause chronic infections that do not respond well to antibiotic therapy.

Prototheca spp. are mastitis-causing pathogens that are classified as achlorophyllic algae. Mastitis infections from Prototheca spp. can occur at any time but will most likely occur when cows have access to wet areas such as stagnant ponds. Because Prototheca spp. are contagious, once a cow becomes infected, other cows are at risk during milking. Prototheca spp. can cause chronic infections that do not respond to current antimicrobial therapies.

Pseudomonas spp. are environmental mastitis-causing pathogens. Pseudomonas spp. has been isolated from milking parlor drop hoses, and is known to cause mastitis through the use of water during milking. Prevention and control of Pseudomonas spp. is based on reducing the exposure of cattle to infected water sources. Pseudomonas spp. does not respond well to antibiotic therapy, thus prevention is key.

Authored by Turner Swartz, former Ph.D. student, Dairy Science, Virginia Tech, and Christina S. Petersson-Wolfe, Associate Professor & Extension Dairy Scientist, School of Animal Science, Virginia Tech. First published April 2016, last reviewed January 2026.

Mastitis cases caused by yeast and mold are typically sporadic and are usually not a significant issue in a herd. Yeast form white or cream-colored colonies that can easily be confused with coagulase-negative staphylococci. Gram staining will differentiate yeast from CNS; yeast are two to three times larger than CNS and typically exhibit budding. Mold colonies can have a fluffy texture and exhibit several different colors.

Environmental Streptococci and Enterococcus spp. are environmental organisms commonly found in organic matter, including bedding. Enterococci are also commonly found in silage inoculants and are associated with plant matter, such as dairy feed. Due to the nature of these bacteria, emphasis needs to be placed on prevention of these infections, rather than focused on treatment.

Streptococcus uberis is an environmental organism commonly found in manure and other organic matter, including bedding. Poor udder cleanliness, inadequate stall management, and damaged teat ends also appear to increase the risk of spreading S. uberis to uninfected cows. These infections are often difficult to cure, and emphasis needs to be placed on prevention rather than treatment.

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