title: Microbiologic investigation of an epizootic of mastitis caused by Serratia marcescens in a dairy herd.
abstract: An epizootic of subclinical and clinical mastitis caused by Serratia marcescens was investigated in a 1,000-cow dairy farm in California. Serratia marcescens was isolated from 13 to 18% of composite milk samples obtained from lactating dairy cows. During monthly milk sampling performed during a 4-month period, S marcescens was isolated from 38.8 to 62.3% of composite milk samples obtained from cows from which S marcescens was previously isolated. Few cows infected with S marcescens had evidence of clinical mastitis. Somatic cell count value was associated with isolation of S marcescens. Cows with somatic cell counts greater than 500,000 were 5.48 times as likely to have intramammary infections with S marcescens, compared with cows with somatic cell count less than or equal to 500,000. Lactation number also was associated with S marcescens intramammary infection. After adjusting for the effect of lactation number, cows with high somatic cell count values were 2.98 times as likely to have intramammary infection with S marcescens, compared with cows with low somatic cell counts. Infection with S marcescens was independent of days in lactation, production string, and daily milk production. Eleven months after the beginning of the epizootic, S marcescens was isolated from organic bedding samples obtained from the dairy. Despite numerous attempts, other sources of S marcescens could not be identified on this dairy.
authors.affiliation: Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Canada.
authors.forename: P L
authors.initials: PL
authors.lastname: Ruegg
authors.forename: W M
authors.initials: WM
authors.lastname: Guterbock
authors.forename: C A
authors.initials: CA
authors.lastname: Holmberg
authors.forename: J M
authors.initials: JM
authors.lastname: Gay
authors.forename: L D
authors.initials: LD
authors.lastname: Weaver
authors.forename: R W
authors.initials: RW
authors.lastname: Walton
mesh_terms: D000818:Animals; D002140:California / Q000453:epidemiology; D002417:Cattle; D002452:Cell Count / Q000662:veterinary; D016009:Chi-Square Distribution; D004196:Disease Outbreaks / Q000662:veterinary*; D005260:Female; D008414:Mastitis, Bovine / Q000453:epidemiology / Q000382:microbiology*; D008892:Milk / Q000166:cytology / Q000382:microbiology*; D016868:Serratia Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D012706:Serratia marcescens / Q000302:isolation & purification*; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013292:Streptococcus agalactiae / Q000302:isolation & purification