Regulation of Cell Growth and Virulence Gene Expression in Staphylococcus aureus by the Iron-Binding Proteins Lactoferrin and Hemin

Staphylococcus aureus is a leading cause of nosocomial infections in the United States, particularly in immune-suppressed patients and preterm infants. S. aureus requires free iron in its environment to thrive and reproduce. In mammals, free iron is sequestered away from pathogens by iron-binding proteins, including hemoglobin and lactoferrin. Lactoferrin has bacteriostatic properties and was shown in randomized controlled clinical trials and subsequent meta-analysis to reduced S. aureus septicemia in preterm infants. Herein, we tested the hypothesis that lactoferrin would reduce the growth of S. aureus in vitro and modulate the expression of iron-regulated surface determinate (Isd) proteins, which are used by S. aureus to cleave heme from the host’s hemoglobin, and gyrA, a marker of cell oxidative stress. S. aureus S54F9 cells were cultured in sow serum in the absence (control; Ctrl) or presence of subphysiological (1 μM), physiological (3 μM), or superphysiological (6 μM) serum concentrations of hemin (HM), lactoferrin (LF), and both proteins (Cmb). Cell growth was assessed every 12 hr. by optical density and cells were harvested after 96 hr. to assess mRNA expression of IsdG, IsdC, and gyrA. LF at both 3 μM and 6 μM and Cmb at 6 μM inhibited cell growth compared to Ctrl. LF and Cmb at 6 μM increased mRNA expression of IsdG and gyrA supporting bacterial adaptations in response to iron sequestration. These findings suggest potential mechanisms whereby lactoferrin prevents S. aureus infection in clinical settings.Ope