Bovine Staphylococcus aureus: association of virulence genes, genotypes and clinical outcome

Based on our clinical experience on bovine mastitis, we hypothesized that subtypes of Staphylococcus aureus (S. aureus) exist which differ in their contagious and pathogenic properties. In order to investigate this hypothesis, we analyzed strains of S. aureus isolated from spontaneous intramammary infection (IMI) with their virulence gene patterns and genotypes obtained by PCR amplification of the 16S-23S rRNA intergenic spacer (RS-PCR). The genotypes were then associated with epidemiological and clinical data including 26 herds. The results demonstrated a high association between genotypes and virulence gene patterns as well as between epidemiological and pathogenic properties of S. aureus. In particular, genotype B was related to high contagiosity and increased pathogenicity whereas the other types (C, OG) were found with infection of single cows. Because of the high clinical relevance, our results indicate the need to subtype the IMI-associated strains of S. aureus in the future.