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Journal of Dairy Science Vol. 85 No. 5 1133-1140
© 2002 by American Dairy Science Association ®
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Influence of Staphylococcus aureus Strain-type on Mammary Quarter Milk Somatic Cell Count and N-acetyl-ß-D-glucosaminidase Activity in Cattle from Eight Dairies

J. R. Middleton 1, L. K. Fox 2, J. M. Gay 2, J. W. Tyler 1, and T. E. Besser 3

1 Department of Veterinary Medicine and Surgery, University of Missouri, Columbia 65211
2 Department of Veterinary Clinical Sciences, Washington State University, Pullman 99164
3 Department of Veterinary Microbiology and Pathology, Washington State University, Pullman 99164

The hypothesis tested was that there are differences in pathogenicity between strains of Staphylococcus aureus that cause bovine mastitis. Mammary quarter milk somatic cell count (SCC) and N-acetyl-ß-D-glucosaminidase (NAGase) activity were used as indicators of the pathogenicity of different strains of S. aureus that infect the bovine udder. Eight commercial dairy herds with a history of S. aureus in bulk tank milk cultures were studied. Initially, composite foremilk samples were collected from all lactating cattle in each herd and cultured for staphylococci. Subsequently, all cows with a coagulase-positive staphylococcal intramammary infection (IMI) at the initial sampling that were still present in the herd of origin had individual mammary quarter foremilk samples collected. Coagulase-positive staphylococcal isolates were confirmed as S. aureus using a commercial biotyping system. Staphylococcus aureus isolates were strain-typed using pulsedfield gel electrophoresis. Mammary quarter milk SCC and N-acetyl-ß-D-glucosaminidase activity were determined for each cow. The difference in mean somatic cell count and mean NAGase activity for mammary quarters infected with the same strain of S. aureus and for uninfected quarters on the same cow was calculated. One-way analysis of variance was used to assess differences between strains within a herd. Overall, no significant differences were found between strains, suggesting that the degree of udder parenchymal injury induced by S. aureus IMI is in general significantly affected by factors other than strain type.

Key Words: Staphylococcus aureus • mastitis • bovine • pathogenicity

Submitted on July 30, 2001
Accepted on December 13, 2001




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Bacterial Genotype Affects the Manifestation and Persistence of Bovine Staphylococcus aureus Intramammary Infection
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[Abstract] [Full Text] [PDF]


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