Molecular epidemiology and antimicrobial susceptibility of Staphylococcus aureus and Escherichia coli isolated from bovine mastitis

Abstract

Brazil is the third largest milk producer in the world and infectious diseases, like bovine mastitis, are extremally important, since causes several economic losses to dairy industry. Besides that, some pathogens involved in mastitis pathogeny can also cause illness in humans, being a public health issue. Therefore, molecular studies that evaluate the dynamic of evolution of these pathogens, as well as distribution and risk factors, are critical to propose control measures and to monitor the interface between human and animal strains. In other to better understand the epidemiology and evolution of two important and zoonotic pathogens of bovine mastitis (Staphylococcus aureus and Escherichia coli) two studies were conducted with strains isolated from dairy farms in Minas Gerais state, Brazil. The first aimed to evaluate the genetic diversity of S. aureus isolated from dairy cows, using Multi-locus sequence typing (MLST), and the antimicrobial susceptibility profiles of these isolates. The second, in turn, aimed to compare the virulence profile and REP-PCR genotypes of E. coli isolated from subclinical mastitis, clinical mastitis isolates and dairy farm environment, and to access the virulence factors and genotypes potentially associated with the subclinical persistence into udder. Results showed a high diversity among bovine mastitis S. aureus and a great number of new STs were found. Proximity between S. aureus isolates from human and animal origin was also observed, as well as high resistance to penicillin and tetracyclines and isolates resistant to methicillin (MRSA). Regarding E. coli, it was observed that flagella seems to be a determinant virulence factor in subclinical and persistent infections by this pathogen in bovine mammary gland. Results of molecular typing by REP-PCR suggest that subclinical mastitis isolates are less genetically diverse than clinical mastitis and dairy farm environmental isolates, although it was not possible to determine a specific genotype associated with subclinical and persistent E. coli mastitis (MPEC).