Prevalence of bacterial mastitis in cattle from the farms around Tehran

To determine the prevalence of bacterial mastitis in cattle, milk samples positive for California mastitistest (CMT) were cultured during a period of almost 4 years. The bacterial species isolated from 2904 milksamples studied were coagulase negative Staphylococcus sp. in 879 (30.27%) samples, Streptococcusagalactiae in 642 (22.11%), S. dysgalactiae in 332 (11.43%), E. coli in 295 (10.16%), Staphylococcus aureusin 84 (2.89%), Bacillus cereus in 51 (1.76%), Arcanobacterium pyogenes in 31 (1.07%), Pseudomonasaeruginosa in 6 (0.21%), Klebsiella pneumoniae in 4 (0.14%), Pasteurella multocida in 1 (0.03%) andMycoplasma 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 contaminationof milk with coagulase negative staphylococci are the most frequent bacterial infection in dairy cattle aroundTehran; it mostly causes subacute form of the disease. S. agalactiae, S. dysgalactiae and E. coli are thesecond, third and the fourth causative agents.