Epidemiological characteristics of bovine clinical mastitis caused by Staphylococcus aureus and Escherichia coli studied by DNA fingerprinting

Abstract

Objective - To study the epidemiology of clinical mastitis caused by Escherichia coli and Staphylococcus aureus by differentiating isolates with DNA fingerprinting techniques, using polymerase chain reaction. Design - Milk samples were collected from cases of clinical mastitis in dairy cows. Escherichia coli and S aureus isolates from these cases were compared within and between cows and herds. Sample Population - Seven dairy herds with an average bulk milk somatic cell count < 150,000/ml, and incidence of cows with clinical mastitis of > 25%/y. Procedure - Chromosomal DNA was isolated from E coli and S aureus strains isolated from cases of clinical mastitis, and amplified by polymerase chain reaction, using enterobacterial repetitive intergenic consensus primers for E coli and a random amplified polymorphic DNA primer for S aureus Escherichia coli and S aureus strains were identified and differentiated, using their DNA polymorphism pattern Results - Multiple E coli genotypes were found in each of the herds. Persistent infections with E coli were sporadic. Only a limited number of different S aureus genotypes was found in each of the herds studied. Recurrent cases of S aureus mastitis were found in 25% of quarters with clinical S aureus mastitis. Comparing S aureus isolates from different herds indicated that 1 S aureus genotype was most prevalent. Conclusions - Because different quarters were infected with different genotypes, it was concluded that E coli is an environmental pathogen, and does not generally spread from quarter to quarter The hypothesis that S aureus mastitis is a contagious disease, spreading from infected to uninfected quarters, could not be rejected.