Prevalence and antibiotic resistance of Staphylococcus aureus and Streptococcus agalactiae in family-owned dairy herds in the state of Minas Gerais, Brazil

Abstract

Bovine mastitis is the most frequent disease in dairy herds worldwide, causing great economic losses to both producers and the industry. This disease has direct implications in public health due to the zoonotic potential of some agents involved in its etiology and the presence of antimicrobial residues in milk. Knowledge of the agents involved in its etiology and the susceptibility profiles to antimicrobials is of paramount importance, give the multifactorial aspect of the disease and the importance of milk production in family farming. This study evaluated the prevalence of Staphylococcus aureus and Streptococcus agalactiae in family-owned herds in the Campo das Vertentes region, State of Minas Gerais, and the resistance of these pathogens to the most commonly used antibiotics in the treatment of mastitis in dairy herds. The study involved 200 properties, covering an area of approximately 12,564 km2 . The prevalence of pathogens was carried out through microbiological analyses of milk samples from each farm’s milk tank. Modified Baird-Parker Agar medium was used to detect S. aureus, and modified Edwards Agar medium, enriched with 5% defibrinated sheep blood, was used to detect S. agalactiae. Disc diffusion method was used to evaluate resistance to antibiotics. The results showed high prevalence of S. aureus pathogens (71.0%) and S. agalactiae (68.0%) as well as high levels of multidrug resistance. The results show that the control of contagious mastitis in the herds is flawed, which indicates the need for more effective control of these pathogens and more judicious use of antibiotics to minimize resistance.