1Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
2Department of Food Hygiene and Public Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
To determine the prevalence of bacterial mastitis in cattle, milk samples positive for California mastitis test (CMT) were cultured during a period of almost 4 years. The bacterial species isolated from 2904 milk samples studied were coagulase negative Staphylococcus sp. in 879 (30.27%) samples, Streptococcus agalactiae in 642 (22.11%), S. dysgalactiae in 332 (11.43%), E. coli in 295 (10.16%), Staphylococcus aureus in 84 (2.89%), Bacillus cereus in 51 (1.76%), Arcanobacterium pyogenes in 31 (1.07%), Pseudomonas aeruginosa in 6 (0.21%), Klebsiella pneumoniae in 4 (0.14%), Pasteurella multocida in 1 (0.03%) and Mycoplasma sp. in another (0.03%) sample. No growth was found in 578 samples (19.90%). Thirty-one (37%) of 84 animals which were infected with S. aureus, had acute infection. We found that contamination of milk with coagulase negative staphylococci are the most frequent bacterial infection in dairy cattle around Tehran; it mostly causes subacute form of the disease. S. agalactiae, S. dysgalactiae and E. coli are the second, third and the fourth causative agents.