Staphylococcus aureus associated with mammary glands of cows: genotyping to distinguish different strains among herds

The hypothesis that strains of Staphylococcus aureus are more likely to be unique to a herd than common to several herds was tested. Herds (n = 28) fr om nine geographic areas of Korea, with elevated milk somatic cell counts ( >500 000 cells/ml) were enrolled in this study. Mammary quarter milk sample s were aseptically collected from all lactating cows (n = 616) with at leas t three functional quarters. Milk was cultured and S. aureus isolates were typed using pulse field gel electrophoresis of DNA SmaI digests. A total of 181 cows were identified as having S. aureus intramammary infections. A to tal of 52 different types of S. aureus were identified and 34 (65.4%) were associated with a single herd. A total of 18 types of S. aureus were found in multiple herds; 14 types were found in two herds, and four types were fo und in three herds. Herds with 1, 2, 3, and more than 3 types, were: four ( 14.3%); eight (28.6%): nine (32.1%); and seven (25.0%). The data indicate t hat the majority of strains were found in one herd only, and more than 90% were found in two or less herds, suggesting that strains of S, aureus are m ore likely to be restricted to a single herd, than found in multiple herds. (C) 2001 Elsevier Science B.V. All rights reserved.