A Critical Role for HlgA in Staphylococcus aureus Pathogenesis Revealed by A Switch in the SaeRS Two-Component Regulatory System

Abstract

Cytolytic pore-forming toxins including alpha hemolysin (Hla) and bicomponent leukotoxins play an important role in the pathogenesis of Staphylococcus aureus. These toxins kill the polymorphonuclear phagocytes (PMNs), disrupt epithelial and endothelial barriers, and lyse erythrocytes to provide iron for bacterial growth. The expression of these toxins is regulated by the two-component sensing systems Sae and Agr. Here, we report that a point mutation (L18P) in SaeS, the histidine kinase sensor of the Sae system, renders the S. aureus Newman hemolytic activity fully independent of Hla and drastically increases the PMN lytic activity. Furthermore, this Hla-independent activity, unlike Hla itself, can lyse human erythrocytes. The Hla-independent activity towards human erythrocytes was also evident in USA300, however, under strict agr control. Gene knockout studies revealed that this Hla-independent Sae-regulated activity was entirely dependent on gamma hemolysin A subunit (HlgA). In contrast, hemolytic activity of Newman towards human erythrocytes from HlgAB resistant donors was completely dependent on agr. The culture supernatant from Newman S. aureus could be neutralized by antisera against two vaccine candidates based on LukS and LukF subunits of Panton-Valentine leukocidin but not by an anti-Hla neutralizing antibody. These findings display the complex involvement of Sae and Agr systems in regulating the virulence of S. aureus and have important implications for vaccine and immunotherapeutics development for S. aureus disease in humans.

Bacterial outer membrane vesicles engineered with lipidated antigens as a platform for Staphylococcus aureus vaccine

“…injection of 2 × 10 8 colony-forming units (CFUs) of S. aureus Newman strain, a strain expressing all 5 antigens (see refs. 31, 33, and 34), and the health status of the animals was followed every day over a period of 7 d using a 1-to-4 pain scale (see Material and Methods ). Animals that reached the pain value of 4 were killed since they reached the “near mortality point” and would have died within 24 h. On the other hand, those animals that maintained a score lower than 4, fully recovered within 7 d. Fig.…”

IBT-V02: A Multicomponent Toxoid Vaccine Protects Against Primary and Secondary Skin Infections Caused by Staphylococcus aureus

“…Prominent among these toxins is Hla, which is the main driver of the skin dermonecrotic lesions caused by SA in mouse and rabbit models ( 35 , 58 ). Hla is highly hemolytic for rabbit red blood cells but not for human erythrocytes ( 59 ), and its main pathogenic activity in humans is likely due to its ability to damage the skin and mucosal barriers by targeting epithelial cells ( 60 – 63 ), endothelium ( 64 , 65 ), and keratinocytes ( 66 ), as well as pro-inflammatory properties through inflammasome activation ( 35 ). Hla also contributes to biofilm formation by SA wound isolates ( 67 ).…”

Differences in virulence between the two more prevalent Staphylococcus aureus clonal complexes in rabbitries (CC121 and CC96) using an experimental model of mammary gland infection

“…Haemolytic assays were carried out as previously described [30]. Briefly, whole blood was washed twice with phosphate-buffered saline (PBS) and resuspended in PBS to obtain 8% (wt/vol.).…”