The Effect of Adding Blood on the Virulence Genes Expression of Staphylococcus aureus in Exponential and Stationary Growth Phase

Background Staphylococcus aureus is an opportunistic pathogen that produces many virulence factors, and the most important regulator system of virulence factors expression in these bacteria is the agr system. Expression of virulence factors is not the same under in vitro conditions in standard laboratory medium and in vivo in the host. Objectives This study aimed at evaluating the effects of adding blood on the virulence genes expression of S. aureus. Methods In this study, the expression levels of agrA, RNAIII, hla (encoding alpha-toxin), spa (encoding protein A), and mecA (encoding resistance of methicillin) genes were determined during growth of S. aureus isolates in BHI broth and BHI broth, containing 5% sheep blood during different growth phases. The gyrB gene was used as an internal control. Results The agr system in the BHI broth, containing 5% sheep blood, was active. The expression levels of agrA, RNAIII, hla, and mecA in the stationary phase relative to exponential phase of growth was increased by 2.95, 5.7, 2.7 and 2.08 folds, respectively. However, the expression of spa gene was decreased by 0.78 folds. Conclusions Aside from the growth phase, the expression levels of all of the genes in cultures containing blood relative to BHI broth alone were increased. During encounter with blood cells, the expression profile was similar to that seen in vivo conditions.