From the NMC Newsletter "Udder Topics", August, 2001

Source
The primary source of Pasteurella species is the upper respiratory tract of mammals and birds.

Means of spread
Unknown; probably from cow to cow. Pasteurella spp. from the respiratory tract of cows could be transported to the udder via bloodstream or lymphatic system and cause intramammary infections under suitable conditions.

Prevention and control measures
Prevent teat injuries. If infection is confirmed, remove affected cows from the herd.

Miscellaneous information
Pasteurella spp. are seldom reported as a cause of bovine mastitis. However, outbreaks in individual herds may occur. Pasteurella spp. may cause acute, severe mastitis. Affected quarters may produce a creamy-yellow, thick, and viscous secretion, sometimes with a foul odor. Agalactia may develop.

Despite Pasteurella spp. sensitivity to several antibiotics in vitro, mastitic cows usually do not respond to intramammary or parenteral treatments. Death may result from endotoxemia.

Culturing comments
Pasteurella spp. produce colonies 2 to 4 mm in diameter. Colonies are grey, very mucoid, and often confluent. irregular, rough colonies may occur. Pasteurella spp. are usually hemolytic and produce a musty odor.

Source: NMC publication “Laboratory Handbook on Bovine Mastitis” pg. 111 (1999)