Comparative secretome analysis of Staphylococcus aureus strains with different within-herd intramammary infection prevalence

Staphylococcus aureus is a major pathogen causing intramammary infection and mastitis in dairy
cows. S. aureus genotypes (GT) can differ significantly in their ability to diffuse and persist in the
herd; while the association of virulence gene carriage with epidemiological behavior remains
unclear, a role for secreted proteins has been postulated. We characterized the secretome of six
S. aureus strains belonging to two genotypes with opposite within-herd prevalence, GTB (high)
and GTS (low), corresponding to sequence types (ST) 8 and 398, by high-resolution tandem mass
spectrometry and differential analysis with Proteome Discoverer. Data are available via
ProteomeXchange with identifier PXD029571. Out of 720 identified proteins, 98 were unique or
more abundant in GTB/ST8 and 68 in GTS/ST398. GTB/ST8 released more immunoglobulinbinding
proteins, complement and antimicrobial peptide inhibitors, enterotoxins, and metabolic
enzymes, while GTS/ST398 released more leukocidins, hemolysins, lipases, and peptidases.
Furthermore, GTB/ST8 released the von Willebrand factor protein, staphylokinase, and clumping
factor B, while GTS released the staphylococcal coagulase and clumping factor A. Hence, GTB/ST8
secretomes indicated a higher propensity for immune evasion and chronicity and GTS/ST398
secretomes for cellular damage and inflammation, consistent with their epidemiological characteristics.
Accordingly, GTS/ST398 secretions were significantly more cytotoxic against bovine
PBMCs in vitro. Our findings confirm the crucial role of extracellular virulence factors in
S. aureus pathogenesis and highlight the need to investigate their differential release adding to
gene carriage for a better understanding of the relationship of S. aureus genotypes with epidemiological
behavior and, possibly, disease severity.