Molecular characterization of Staphylococcus aureus and Streptococcus uberis isolates of INTRAMMARY infections of dairy cows

Abstract

Bovine mastitis is one of diseases that most affects dairy herds and has a great impact on the economy of the activity, as it affects the milk production and quality of dairy products. The majority of mastitis cases has bacterial origin and its resolution depends on some factors, such as a bacterial strain involved in the infection, the period of infection, and the susceptibility of the host. The objectives of the present study are: (A) to characterize the genotypic variability of strains with identification of Staphylococcus aureus and Streptococcus uberis isolated from cases of clinical and subclinical mastitis in herds of Brazil and other countries; (B) to evaluate the risk of persistence and new intramammary infections through the evaluation of Staph aureus identified before and after treatment of subclinical mastitis, based on molecular methods of genotyping; (C) to determine virulence factors associated with Staph aureus isolates. The study will be conducted by three experiments: 1 - Genotypic determination of Staph aureus isolates from clinical and subclinical mastitis of Brazilian herds in comparison with isolates from other countries; 2 - Genotypic molecular characterization of Staph aureus isolates for evaluation of risk of persistence and new intramammary infections, antimicrobial susceptibility, and virulence factors; 3 - Determination of the genotypic diversity of Strep uberis identified from intramammary infections in dairy cows from Brazil and Portugal. For the experiment 1, 70 Staph aureus strains (35 of clinical mastitis and 35 of subclinical mastitis) will be isolated from milk samples of cows from different herds and geographic regions of Brazil. For each strain information at the cow- and treatment-level will be collected, such as the date of isolation, mastitis form (clinical or subclinical), parity, individual somatic cell count (SCC), severity (for clinical cases) and treatment history. For experiment 2, Staph. aureus strains will be genotyped by the technique of pulsed field gel electrophoresis (PFGE), and submitted to evaluation of antimicrobial sensitivity analysis. In the experiment 3, approximately 50 strains of Strep. uberis will be genotypically characterized for evaluation of strain diversity, which will be associated with mastitis severity. (AU)