title: Diurnal differences in milk composition and its influence on in vitro growth of Staphylococcus aureus and Escherichia coli in bovine quarter milk.
abstract: In experimental intramammary inoculation studies, it has been observed that mastitis susceptibility is influenced, among others, by cow factors. To identify milk characteristics leading to these differences, quarter milk samples of morning and evening milk were collected and analyzed for their composition (protein, fat, lactose, urea, lactoferrin, lactoperoxidase, and β-lactoglobulin concentrations), somatic cell count, and antibodies against Staphylococcus aureus. Furthermore, in vitro growth of S. aureus and Escherichia coli in fresh quarter milk samples was determined. All measured parameters differed significantly between quarters and also between morning and evening milk with the exception of lactose levels. In addition, quantitative growth of S. aureus and E. coli was significantly different in morning milk compared with evening milk. Mixed model analysis revealed that replication of S. aureus was negatively associated with the presence of fat, S. aureus-specific IgG1 antibodies, contamination of the milk sample and morning milk. Replication of E. coli was negatively associated with fat concentrations, and positively associated with morning milk. The significant difference between morning and evening milk supports the theory that changes in milk composition influence bacterial growth. Although all determined milk components differed significantly between quarters and in time no significant association with bacterial growth could be identified with the exception of fat for both studied species and IgG1 titers for S. aureus. The negative association of fat with bacterial growth was assumed to occur due to activation of lipolysis by milk handling and can most likely be neglected for in vivo relevance. The fact that S. aureus-specific IgG1 titers were negatively associated with S. aureus growth in vitro encourages the ongoing effort to develop a vaccine against S. aureus-induced mastitis.
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, the Netherlands. Electronic address: s.w.f.eisenberg@gmx.de.
authors.forename: S W F
authors.initials: SWF
authors.lastname: Eisenberg
authors.affiliation: Ruminant Research and Development, MSD Animal Health, Wim de Körverstraat 35, 5830 AA Boxmeer, the Netherlands; Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, the Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: Boerhout
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, the Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Ravesloot
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, the Netherlands.
authors.forename: A J J M
authors.initials: AJJM
authors.lastname: Daemen
authors.affiliation: Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, the Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Benedictus
authors.affiliation: Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, the Netherlands; Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa.
authors.forename: V P M G
authors.initials: VPMG
authors.lastname: Rutten
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, the Netherlands; Department of Bacteriology and Epidemiology, Central Veterinary Institute part of Wageningen UR, Edelhertweg 15, PO Box 65, 8200 AB Lelystad, the Netherlands.
authors.forename: A P
authors.initials: AP
authors.lastname: Koets
mesh_terms: D000818:Animals; D002417:Cattle; D004926:Escherichia coli; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology; D008892:Milk / Q000737:chemistry* / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000276:immunology*
keywords: Escherichia coli; Staphylococcus aureus; bovine; milk composition