Novel sequence types (STs) ofStaphylococcus aureusisolates causing clinical and subclinical mastitis in flocks of sheep in the northeast of Brazil

Abstract

Staphylococcus aureusis one of the most important infectious mastitis causative agents in small ruminants. In order to know the distribution ofStaph. aureusstrains associated with infectious mastitis in flocks of sheep in the northeast of Brazil and establish whether these clones are related to the strains distributed internationally, this study analysed the genetic diversity ofStaph. aureusisolates from cases of clinical and subclinical mastitis in ewes by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). In this research, 135 ewes with mastitis from 31 sheep flocks distributed in 15 districts were examined.Staph. aureuswas isolated from sheep milk in 9 (29%) out of 31 herds located in 47% of the districts surveyed. MLST analysis allowed the identification of four STs (ST750, ST1728, ST1729 and ST1730). The last three with their respective novel alleles (glp-220;pta-182 andyqil-180) were recently reported in theStaph. aureusMLST database (http://www.mlst.net). Each novel allele showed only a nucleotide different from those already described. The occurrence of CC133 (ST750 and ST1729) in this study is in agreement with other reports that only a few clones ofStaph. aureusseem to be responsible for most cases of mastitis in dairy farms and that some of these clones may have broad geographic distribution. However, the prevalence of CC5 (ST1728 and ST1730)—an important group related to cases of colonization or infection in humans—differs from previous studies by its widespread occurrence and may suggest human contamination followed by selective pressures of the allelic diversifications presented for these STs.