Immunoproteomic analysis of the secretome of bovine-adapted strains of Staphylococcus aureus demonstrates a strain-specific humoral response

Staphylococcus aureus is a common pathogen associated with bovine intramammary infection. A number of distinct S. aureus lineages are associated with such infections although there is a dearth of knowledge regarding the major immunogenic antigens associated with each lineage and whether these antigens provide protection against heterologous strains. Identification of the major immunogenic antigens of the predominant bovine adapted S. aureus lineages would assist in the design of effective vaccines and diagnostic tests to control intramammary infections caused by S. aureus. The aim of this study was to characterise the serum IgG response to S. aureus extracellular proteins in cows infected with strains from different lineages, as well as to identify antigenic proteins produced by these strains. Genotypic characterisation found that strain MOK124 (CC151) encoded more toxins, including the ruminant-specific leukocidin LukMF, compared to strain MOK023 (CC97). In addition, MOK124 secreted more toxins in vitro, compared to MOK023. Immunoproteomic analysis was performed using sera from cows infected with either MOK023 or MOK124. One-dimensional serum blotting revealed that cows infected with MOK023 predominantly generated a humoral response against high molecular weight proteins while cows infected with MOK124 primarily generated a humoral response against low molecular weight proteins. Two-dimensional serum blotting demonstrated that antibodies produced by an MOK023 infected cow could cross react with some of the extracellular proteins produced by MOK124 and vice versa. Mass spectrometry analysis of immunoreactive proteins identified common candidate immunogens produced by both strains, including alpha-hemolysin and beta-hemolysin. In addition, strain-specific candidate immunogens were also identified. This study demonstrates that genes encoding important S. aureus secreted virulence factors, the production of cognate gene products, and the humoral immune response to infection is, to an extent, strain dependent. However, the identification of some common candidate immunogens suggests that there are proteins that can be exploited for further vaccine or diagnostic research that targets S. aureus strains from a variety of lineages.

Automated summary

This study aimed to characterize the serum IgG response to extracellular proteins of different lineages of Staphylococcus aureus in cows infected with these strains, as well as to identify antigenic proteins produced by these strains. The results showed that the humoral immune response in infected cows varied depending on the strain, with some generating a response against high molecular weight proteins and others against low molecular weight proteins. Common candidate immunogens, as well as strain-specific candidate immunogens, were identified.