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Staphylococcus aureus shedding pattern throughout lactation in dairy cows with naturally occurring intramammary infection

Jennifer B. WalkerDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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William L. WalkerDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Fred J. DeGravesDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Jennifer L. MathewsDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Wondwossen A. GebreyesDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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Päivi J. Rajala-SchultzDepartment of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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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.

Design—Longitudinal field study.

Sample—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 and Clinical RelevanceS 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.

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.

Design—Longitudinal field study.

Sample—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 and Clinical RelevanceS 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.

Contributor Notes

Dr. Jennifer Walker's present address is Dean Foods Co, 2711 N Haskell Ave, Ste 3400, Dallas, TX 75204.

Dr. DeGraves’ present address is Department of Agriculture, Ogden College of Science and Engineering, Western Kentucky University, Bowling Green, KY 42101.

Supported by USDA Animal Health Formula Funds through the Council for Research at the College of Veterinary Medicine, The Ohio State University, and grants provided by COBA/Select Sires, the Ohio Dairy Producers Association, and the Helwig Foundation.

Presented in part at the 43rd Annual American Association of Bovine Practitioners Conference, Albuquerque, August 2010.

Address correspondence to Dr. Jennifer Walker (jennifer_walker@deanfoods.com).