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Infection and Immunity, June 2006, p. 3507-3512, Vol. 74, No. 6
0019-9567/06/$08.00+0     doi:10.1128/IAI.01726-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Staphylococcus aureus Enterotoxin D Is Secreted in Milk and Stimulates Specific Antibody Responses in Cows in the Course of Experimental Intramammary Infection

Tore Tollersrud,^1* Annette H. Kampen,¹ and Kevin Kenny^2,

Department of Animal Health, National Veterinary Institute, Oslo, Norway,¹ Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New Yok 14853²

Received 21 October 2005/ Returned for modification 19 January 2006/ Accepted 29 March 2006

An enterotoxin D (SED)-producing strain of Staphylococcus aureus was used to infect one mammary gland of each of 17 lactating dairy cows. All glands became infected and shed bacteria over a sampling period of 3 weeks. Serum and milk antibodies specific for SED were monitored by an enzyme-linked immunosorbent assay for 12 weeks. Elevated anti-SED antibodies were detected in all cows after infection, and immunoglobulin of the G2 subclass comprised most of the specific serum response. SED was detected in mastitic milk samples from two cows at levels of 5 to 10 ng/ml. An in vitro lymphocyte proliferation assay showed that SED at levels below 10 pg/ml induced proliferation of bovine lymphocytes and that sheep antiserum specific for SED neutralized this proliferative response. Sera obtained from the cows pre- and postinfection inhibited lymphocyte proliferation at SED concentrations of 10 and 50 ng/ml, respectively. The addition of SED to whole blood or to isolated neutrophils had no significant effect on neutrophil function in vitro. The results show that SED is secreted during mammary gland infection, is mitogenic for bovine lymphocytes, and stimulates the production of specific antibodies.

Editor: F. C. Fang

Present address: Department of Agriculture and Food, Abbotstown, Dublin 15, Ireland.