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Updated: Jan 6, 2026
Invasion of Human Cells by a Bacterial Pathogen
Published on: March 21, 2011
MgrA Negatively Impacts Staphylococcus aureus Invasion by Regulating Capsule and FnbA
Mei G Lei1, Dereje D Gudeta1, Thanh T Luong1
1Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Abstract:
Virulence genes are regulated by a complex regulatory network in Staphylococcus aureus Some of the regulators are global in nature and affect many downstream genes. MgrA is a multiple-gene regulator that has been shown to activate genes involved in capsule biosynthesis and repress surface protein genes. The goal of this study was to demonstrate the biological significance of MgrA regulation of capsule and surface proteins. We found that strain Becker possessed one fibronectin-binding protein, FnbA, and that FnbA was the predominant protein involved in invasion of nonphagocytic HeLa cells. By genetic analysis of strains with different amounts of capsule, we demonstrated that capsule impeded invasion of HeLa cells by masking the bacterial cell wall-anchored protein FnbA. Using variants with different levels of mgrA transcription, we further demonstrated that MgrA negatively impacted invasion by activating the cap genes involved in capsule biosynthesis and repressing the fnbA gene. Thus, we conclude that MgrA negatively impacts cell invasion of S. aureus Becker by promoting capsule and repressing FnbA.
Insights
Staphylococcus aureus MgrA regulator negatively impacts invasion by increasing capsule production and decreasing fibronectin-binding protein A. This highlights MgrA
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- Virulence gene regulation in *Staphylococcus aureus* involves complex networks with global regulators like MgrA.
- MgrA is known to influence capsule biosynthesis and surface protein expression.
- Understanding MgrA's role is crucial for deciphering *S. aureus* pathogenicity.
Purpose of the Study:
- To elucidate the biological significance of MgrA's regulation on capsule and surface protein expression.
- To determine MgrA's impact on *Staphylococcus aureus* invasion of nonphagocytic cells.
Main Methods:
- Genetic analysis of *Staphylococcus aureus* strains with varying *mgrA* transcript levels and capsule amounts.
- Assessment of bacterial invasion into HeLa cells.
- Identification and characterization of fibronectin-binding protein A (FnbA) and its role in invasion.
Main Results:
- Capsule production was found to impede *S. aureus* invasion by masking the FnbA protein.
- MgrA activation of *cap* genes (capsule biosynthesis) and repression of *fnbA* gene were demonstrated.
- Increased capsule and decreased FnbA, mediated by MgrA, negatively impacted bacterial cell invasion.
Conclusions:
- MgrA negatively regulates *S. aureus* Becker cell invasion.
- This negative impact is achieved through MgrA-mediated promotion of capsule synthesis and repression of FnbA.
- MgrA acts as a key virulence regulator controlling bacterial adherence and host cell interaction.
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