Characterization of Virulence Factors and Antimicrobial Resistance in Staphylococcus aureus Isolated from Bulk Tank Milk of Dairy Farms.

• Grant number: 25/00138-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2025
• End date: December 31, 2025
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
• Principal Investigator: Marcos Veiga dos Santos
• Grantee: Inara Araújo Mota
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 21/05400-3 - Responsible use of antimicrobials and bacterial resistance in dairy herds, AP.TEM

Abstract

Staphylococcus aureus (S.aureus) is one of the primary pathogens associated with bovine mastitis, a disease with significant economic and health impacts on the dairy industry. This microorganism exhibits various virulence factors, including enterotoxins, intracellular adhesion proteins, fibronectin, aggregation proteins, and hemolysins. Additionally, S. aureus can form biofilms, three-dimensional structures composed of polysaccharides, proteins, and lipids that confer resistance to antimicrobial agents and protection from external environments. These biofilms are crucial for bacterial persistence on food industry equipment surfaces, increasing the risk of cross-contamination. Moreover, antimicrobial resistance to ¿-lactams, tetracyclines, and aminoglycosides compromises the efficacy of conventional treatments and contributes to the severity of infections. Antimicrobial resistance in S. aureus is strongly associated with the inappropriate use of antibiotics in the dairy sector, particularly for treating clinical mastitis and during drying-off periods, posing a challenge to public and animal health. Given this context, this study aims to evaluate the frequency of genes associated with virulence and antimicrobial resistance and the ability to form biofilms in S. aureus isolates from dairy farm tanks. The analyzed genes include those related to enterotoxin production (sea, seb, sec, sed, see, seg, seh, sei, sej), intracellular adhesion (icaA, icaD), fibronectin (fnbA, fnbB), aggregation (clfA, clfB), and antimicrobial resistance to ¿-lactams (mecA, blaZ, mecC), tetracyclines (tetK, tetL, tetM), and aminoglycosides (aacA-aphD, aadD, aphA3). To achieve these objectives, 60 S. aureus strains will be analyzed from farms' 83 bulk tank milk samples. The investigation will use conventional PCR techniques, with amplicons detected by agarose gel electrophoresis. Biofilm production will be assessed through microplate cultivation, and results will be analyzed using an ELISA reader. All results will be processed and analyzed using Python (v.3.12.7).