Diversidade genética e caracterização da virulência em Staphylococcus aureus isolados de mastite em rebanhos bovinos brasileiros

Abstract

The bovine mastitis is the disease of greatest economic impact for dairy herds worldwide and Staphylococcus aureus is one of its main etiological agents. This pathogen has a variety of virulence factors that lead to clinical or subclinical mastitis, and chronic intramammaryinfections of difficult treatment. In addition to mastitis, this agent is responsible for other diseases in animals and man, such as endocarditis, osteomyelitis and septicemia, being quite important for public health. The objectives of this work were to accomplish the phenotypic characterization, using the experimental model of Galleria mellonella larvae and genotypic using the Pulsed-field Gel Electrophoresis (PFGE), Multiple Locus VNTR fingerprinting (MLVF) and prospect of virulence genes encoding adhesins and toxins in two populations of S. aureus from bovine mastitis, isolated between 1994 and 2014, being one restricted to the State of Minas Gerais, containing isolates of clinical and subclinical origin and one containing subclinical mastitis isolates from herds of seven Brazilian states. The results of the phenotypic analyzes showed that G. mellonella larvae constitute a practical and efficient model to evaluate virulence phenotypes in S. aureus isolates from bovine mastitis, allowing the distinction of more and less virulent isolates. The experimental infection in G. mellonellashowed the predominance of more virulent strains among those coming from subclinical mastitis. The genotyping techniques used were effective for the characterization of S. aureus and indicated the existence of predominant genetic types widely disseminated among different herds. Although PFGE was slightly more discriminatory, MLVF also was confirmed as a good typing technique, allowing a clustering that partially reflected the clustering demonstrated by PFGE. The MLVF, with a level of similarity of 80%, showed a cluster with predominance of clinical strains and another with predominance of subclinical strains. The set of virulence genes encoding agglutination factors (ClfA and ClfB), fibronectin binding protein (FnBPA), toxins (Hla, Hlb and Luk-ED), elastin binding protein (Ebps), and the collagen binding protein (Cna) was widely present in the population of subclinical mastitis isolates from seven Brazilian states and the frequency of these genes ranged from 58 to 97.7%. The results show that this set of proteins should be better evaluated and may be promising as a set of antigens to constitute news vaccines for prevention of mastitis caused by S. aureus in Brazilian dairy herds. In conclusion, this work contributed to the understanding of the epidemiology of bovine mastitis in Brazil, showing the great genetic diversity of the isolates that cause mastitis in the country, but with a predominance of specialized strains that should be better studied for the development of new forms of control and prevention of this disease.