The dynamics of Staphylococcus aureus intramammary infection in nine Danish dairy herds

The aim of the present study was to examine the diversity of Smphylococcns auveus isolates from bovine intramammary infections (IMI) in nine dairy her ds, and compare these with isolates from other sites on the cows by phage- and ribotyping. Whether colonisation of milkers with S. aureus could be a s ource of infection for bovine IMI was investigated. In addition, 100 epidem iologically unrelated S. aureus isolates from asymptomatic human carriers w ere also phage- and ribotyped to compare the human and bovine reservoir of S. aureus in Denmark. A total of 625 S. aureus isolates from bovine IMI, bo vine skin lesions, milking personnel, and non-farm-related human carriers w ere included in the study. Certain types predominated in one or several her ds during the study period of one-and-a-half to two years, whereas the pres ence of other types was of a more sporadic nature. Within the individual he rds, there was a close correspondence between ribo- and phage types of S. a ureus isolated from bovine intramammmary infections and skin lesions. Isola tes from milking personnel, however, were not identical to any of the predo minant intramammary strains. Furthermore, several of the isolates from milk ing personnel showed ribo- and phage patterns identical to S. aureus isolat es from human carriers. The findings of the present study underline the imp ortance of strict milking hygiene and improvement of current mastitis thera py. The results support the hypothesis that some S. aureus mastitis strains are more contagious, virulent or persistent than others, The human reservo ir of S, aureus does not play a major role as a source of bovine intramamma ry infections. (C) 2000 Elsevier Science B.V. All rights reserved.