Fine-tuned characterization of Staphylococcus aureus Newbould 305, a strain associated with mild and chronic mastitis in bovines

Abstract

S. aureus is a major aetiological agent of ruminant mastitis worldwide. The chronic nature of S. aureus mastitis makes it difficult to cure and prone to resurgence. In order to identify the bacterial factors involved in this chronicity, Newbould 305 (N305), a strain that can reproducibly induce mild and chronic mastitis in an experimental setting, was characterized in depth. We employed genomic and proteomic techniques combined with phenotype characterization, in order to comprehensively analyse N305. The results were compared with data obtained on S. aureus RF122, a strain representative of the major clone involved in severe bovine mastitis worldwide. Five mobile genetic elements were identified in the N305 genome as carrying virulence factors which correlated with phenotypic features such as cytotoxicity, mammary epithelial cell invasion or host-adaptation. In particular, the presence and characteristics of surface exposed proteins correlated well with the greater adhesion and internalization capacities of N305 in bovine mammary epithelial cells. N305 also displayed less diversity of toxin genes but secreted larger quantities of these toxins, associated with a higher cytotoxicity potential. Our data are consistent with the invasiveness and host-adaptation features which contribute to the chronicity of S. aureus mastitis. Mobile genetic elements, exoproteins and surface exposed proteins constitute good targets for further research to explore the underlying mechanisms related to mastitis chronicity.

LukMF′ is the major secreted leukocidin of bovine Staphylococcus aureus and is produced in vivo during bovine mastitis

“…LukMF′-negative strains, such as Newbould, also cause mastitis in cattle, showing that LukMF′ is not a prerequisite for S. aureus to cause an intramammary infection and that other toxins or virulence factors also play a role in the pathogenesis of mastitis. However, whereas the LukMF′-negative strain Newbould causes mostly mild clinical symptoms38, infections with the LukMF′-positive isolates RF122 and Ch122 are characterised by severe forms of mastitis3839. In accordance with our results, Rainard et al 39.…”

Existence of two groups of Staphylococcus aureus strains isolated from bovine mastitis based on biofilm formation, intracellular survival, capsular profile and agr-typing

“…Nevertheless, four genes are specific to one group or the other ("cap5-agrI" or "cap8-agrII"): lukM to "cap8-agrII" and hld, clfA and sdrC to "cap5-agrI". These results are in accordance with the study published by Peton et al (2014) in which they have compared two S. aureus bovine strains, N305 that produces mild and chronic mastitis and RF122 that produces severe mastitis. In their study, lukM is present in RF122 and absent in N305.…”

Draft Genome Sequences of Staphylococcus aureus Strains Isolated from Subclinical Bovine Mastitis in Brazil

“…We also genotyped the strains against the reference genome of S. aureus RF122 (accession no. NC_007622), a strain representative of the major clone involved in severe bovine mastitis worldwide ( 10 ). We identified single-nucleotide polymorphisms (SNPs) that resulted in amino acid changes in the coded protein.…”