From the NMC Newsletter "Udder Topics", June, 2000

Source
The primary source of Bacillus species and other Gram-positive bacilli are soil, water, dust, air, feces, vegetation, wounds and abscesses.

Means of spread
Introduction of Gram-positive bacilli into the udder often results from contaminated treatment or treatment devices and improper teat sanitation prior to intramammary treatment.

Basic prevention and control measures
If multiple cases occur, identify and eliminate the sources of infection. Aseptic treatment infusion with single dose sterile treatment tubes should be used to prevent new infections, since contaminated antibiotic preparations are a common source of bacilli.

Miscellaneous information
Bacillus cereus may cause acute and sometimes fatal gangrenous mastitis. Bacillus spp. other than B. cereus and B. subtilis rarely cause intramammary infection. Spores are resistant to heat and chemical disinfectants.

Culturing comments
Bacillus cereus colonies are large, slightly grey with irregular edges, and often surrounded by a clear zone of hemolysis. Bacillus subtilis colonies are greenish-grey with a ground-glass appearance. These bacteria are catalase positive. Microscopic examination of culture growth show large, broad, Gram-positive, endospore-forming rods that tend to form chains. Bacillus cereus are Gram variable.

Other comments
The variety of tests required for species level identification of Gram-positive bacilli are beyond the capabilities for most animal diagnostic laboratories.

Source: National Mastitis Council Publication "Laboratory Handbook on Bovine Mastitis" (1999) pg. 147-149.