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

Arundhathi Venkatasubramaniam,M Javad Aman,Tulasikumari Kanipakala,Rana Mehr,Rajan P Adhikari,Subramaniam Krishnan,Nader Ganjbaksh,Taeok Bae,Ipsita Mukherjee

doi:10.3390/toxins10090377

Arundhathi Venkatasubramaniam, M Javad Aman + Show 7 more

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https://doi.org/10.3390/toxins10090377

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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.

Highlights

Staphylococcus aureus (S. aureus) is an opportunistic human pathogen that can cause a variety of acute and chronic infections [1,2,3,4,5]
We found that supernatant collected from the Newman strain can lyse rabbit and human red blood cells (RBC) in a Hla-independent manner
While evaluating a panel of anti-Hla neutralizing antibodies we noted that hemolytic activity of supernatants from the Newman anti-Hla neutralizing antibodies we noted that hemolytic activity of supernatants from the Newman culture cannot be neutralized by our anti-Hla monoclonal antibodies or even by polyclonal anti-Hla culture cannot be neutralized by our anti-Hla monoclonal antibodies or even by polyclonal anti-Hla

Summary

Introduction

Staphylococcus aureus (S. aureus) is an opportunistic human pathogen that can cause a variety of acute and chronic infections [1,2,3,4,5]. Because of its high adaptability and genomic plasticity, S. aureus has been able to acquire resistance to commonly prescribed antibiotics [6,7,8], and has already emerged as a multi drug resistant “superbug”. In addition to the antibiotic treatments, therapeutic options including active immunization and passive immunotherapy have been applied, but neither of these methods has been successful. Vaccine approaches that target surface antigens of S. aureus, failed in clinical trials, and appear to exacerbate the fatal sequelae of the disease [9]. This concern has been further reinforced in animal studies using cell-associated antigens [10,11].

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