From the NMC Newsletter "Udder Topics", June 2002

Source
Serratia species are Gram-negative environmental pathogens that commonly inhabit soil and plants.

Means of spread
Exposure of teats to Serratia spp. occurs primarily between milkings as teats contact the environmental sources.

Prevention and control measures
The most effective means of reducing the rate of intramammary infections is by keeping cows clean and dry to decrease teat end exposure. Effective environmental sanitation practices include the use of inorganic bedding; avoiding overcrowding of cows; frequent removal of manure and urine; and preventing access to muddy lots or corrals, wet areas under shades, marshy areas, and pools of standing water. The use of an effective germicidal predip and thoroughly drying teats prior to milking may reduce new infections during lactation. Immunization of cows with rough mutants such as E. coli J5 can reduce incidence and severity of clinical cases caused by many Gram-negative mastitis-causing bacteria.

Some strains of Serratia spp. are resistant to germicides containing chlorhexidine gluconate. Avoid teat dips containing chlorhexidine gluconate if Serratia spp. mastitis is suspected in a herd. Regardless of the teat antiseptic product used in a herd, thoroughly wash and air dry teat dip cups between milkings to reduce exposure to these pathogens.

Miscellaneous information
Serratia spp. often cause chronic infections lasting several lactations. Infection rates are higher during the dry period than during lactation. Serratia spp. infections respond poorly to antibiotic therapy.

Source: NMC publication "Laboratory Handbook on Bovine Mastitis" pg. 99 (1999)