title: Staphylococcus aureus shedding pattern throughout lactation in dairy cows with naturally occurring intramammary infection.
abstract: OBJECTIVE
  To evaluate shedding patterns of Staphylococcus aureus, specifically the association between clonal relatedness and shedding patterns of S aureus for cows with naturally occurring S aureus intramammary infection.
  
  
  METHODS
  Longitudinal field study.
  
  
  METHODS
  Milk samples from 22 lactating cows (29 mammary glands) of varied numbers of lactations on 2 dairies. Procedures-Foremilk samples were collected weekly for 26 to 44 weeks during lactation from individual mammary glands. Milk samples were cultured bacteriologically with a 0.01-mL inoculum. Samples were considered culture positive for S aureus if ≥ 1 colony-forming units were obtained. Milk samples from known S aureus-positive mammary glands that were culture negative for S aureus or culture positive with a single colony of S aureus were cultured bacteriologically a second time with a 0.1-mL inoculum. Longitudinal shedding patterns of S aureus and the effect of strain type on ln(colony forming unit count) were examined.
  
  
  RESULTS
  With the 0.01-mL inoculum, 914 of 1,070 (85%) samples were culture positive. After reculturing of negative samples with a 0.1-mL inoculum, 1,011 (95%) of the samples were culture positive. There was no significant difference in the detection of S aureus between genotypic clusters when either the 0.01- or 0.1-mL inoculum was used. There was no significant difference in the amount of shedding between mammary glands infected with isolates in genotypic cluster 1 or 2. No consistent shedding patterns were identified among or within cows. There was a significant difference in mammary gland linear score and test day (composite) linear score between mammary glands infected with isolates in genotypic clusters 1 and 2.
  
  
  CONCLUSIONS
  S aureus was shed consistently in cows with naturally occurring intramammary infection in cows, and regardless of the pulsotype, variations in the amount of S aureus shedding had no significant effect on the ability to detect S aureus with a 0.1-mL inoculum.
authors: Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA. jennifer_walker@deanfoods.com
authors: Jennifer B
authors: JB
authors: Walker
authors: William L
authors: WL
authors: Walker
authors: Fred J
authors: FJ
authors: DeGraves
authors: Jennifer L
authors: JL
authors: Mathews
authors: Wondwossen A
authors: WA
authors: Gebreyes
authors: Päivi J
authors: PJ
authors: Rajala-Schultz
mesh_terms: D000818:Animals; D057138:Bacterial Shedding; D002417:Cattle; D003612:Dairying; D005260:Female; D007774:Lactation; D008414:Mastitis, Bovine / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*