Transcriptional profiles of regulatory and virulence factors of Staphylococcus aureus of bovine origin: oxygen impact and strain-to-strain variations.

Staphylococcus aureus is responsible for a large panel of infections in humans and animals. In cows, S. aureus provokes chronic intramammary infections. Little information is available about the regulation of virulence factors in bovine isolates. Moreover, oxygenation, which is low in an inflamed mammary gland, could play an important role during the infectious process. We investigated the impact of oxygen on regulatory and virulence factors transcription for three S. aureus bovine isolates cultivated in CYPG medium into a fermentor under moderate oxygenation or low oxygenation. A selective panel of regulatory factors and virulence factors was studied through their mRNA profiles by real-time PCR according to growth phases and oxygenation. RNAIII, rot and sarR genes, for the regulatory factors, and asp23 and cflA genes, for the virulence factors, were strongly expressed, whatever the oxygenation and the strains. Under low oxygenation, whatever the strain, an enhanced expression of srr, clfA and spa genes was detected. Some regulators such as sae, sarA and sigB were differentially transcribed according to the strain and the oxygenation condition. This study sustains the complexity of S. aureus genes global regulation and suggests the coexistence of different pathways that can be activated depending on the strain and the oxygen availability.