Abstract The purpose of our study was to investigate the changes of plasma protein from the cows infected with Staphylococcus aureus. Dairy cows shown to be S. aureus-positive on bacteriological culture of milk from all 4 quarters, were classified as S. aureus subclinical mastitis. Two-dimensional gel electrophoresis was used to separate plasma protein from S. aureus subclinical mastitis and healthy dairy cows, and stained with Coomassie Blue G-250 solution. Differential expression proteins were detected by PDQuest 8.0 software and identified by ion trap mass spectrometer. The results showed that the ten protein spots were changed in cows subclinically infected with S. aureus mastitis, and six spots were identified as four proteins including haptoglobin, alpha 1 acid glycoprotein, transthyretin and serum amyloid protein A. Haptoglobin, alpha 1 acid glycoprotein, and serum amyloid protein A were up-regulated in plasma from S. aureus infected cows. ELISA detection of plasma haptoglobin showed that expression of haptoglobin was significantly higher in S. aureus infected cows than that in healthy controls (P<0.01). Dairy cows infected with S. aureus mastitis altered the protein level in plasma suggested that these differential proteins may be useful to clarify the host defense mechanisms and the response to invasion of mammary tissues by S. aureus mastitis.
