Comparison of Staphylococcus aureus Surface Protein ExtractionMethods

Staphylococcus aureus is the major contagious bovine mastitis pathogen and has no effective vaccine. Strainvariation and limited knowledge of common immunogenic antigen/s are among major constraints for developingeffective vaccines. S. aureus cell surface proteins that are exposed to the host immune system constitute goodvaccine candidates. The objective of this study was to compare S. aureus surface protein extraction methods andevaluate immune-reactivity of extracted proteins. Surface proteins were extracted from nine genetically distinct S.aureus strains from cases of bovine mastitis. After extraction, bacterial cell integrity was examined by Gram stainingand electron microscopy to determine if extraction methods caused damage to cells that may release non-surfaceproteins. The extracted proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE) and evaluated for immune-reactivity using western blot. Results showed that all three extractionmethods provided multiple protein bands on SDS-PAGE. Western blot result showed several immuno-reactivesurface proteins, in which some proteins strongly (well-resolved, thick, dark and intense band) reacted across thenine strains tested. The three methods are valid for the extraction of surface proteins and hexadecane and cholicacid methods are more feasible than biotinylation since both are easier, cheaper and have minor effects on thebacterial cell. Strongly immune-reactive surface proteins may serve as potential candidates for a vaccine to controlS. aureus mastitis in dairy cows.