Characterization of the Atl-mediated staphylococcal internalization mechanism.

Area of Science:

• Microbiology
• Cell Biology
• Infectious Diseases

Background:

• Staphylococcus aureus internalization by non-professional phagocytes is a key mechanism in chronic infections.
• The established pathway involves fibronectin (Fn)-binding proteins (FnBPs), fibronectin, and host α5β1 integrin.
• An alternative Atl-dependent internalization mechanism involving heat shock cognate protein 70 (Hsc70) was previously identified.

Purpose of the Study:

• To further characterize the Atl-dependent internalization mechanism of Staphylococcus.
• To quantify the adhesive properties of Atl and identify interacting host cell molecules.
• To elucidate the cellular pathways and machinery involved in Atl-mediated bacterial uptake.

Main Methods:

• Biomolecular interaction analysis (BIA) to assess Atl binding affinities.
• Confocal laser scanning microscopy (CLSM) for visualizing bacterial internalization.
• Flow-cytometric internalization assays with pharmacological inhibitors.
• Investigation of signaling pathways (Src, PI3 kinase) and endocytic machinery (clathrin, actin, microtubules).

Main Results:

• Atl exhibits multivalent, high-affinity interactions with fibronectin (Fn) and Hsc70.
• Atl-dependent internalization involves α5β1 integrin, Fn, Hsc70, Src, and PI3 kinases.
• The process utilizes clathrin-dependent endocytosis, actin rearrangements, and microtubules.
• This mechanism is also employed by Staphylococcus epidermidis, potentially as its primary uptake route.

Conclusions:

• The major autolysin (Atl) mediates Staphylococcus internalization via interactions with fibronectin and Hsc70.
• This Atl-dependent pathway is crucial for bacterial uptake, especially in strains lacking FnBPs.
• The mechanism shares features with FnBP-mediated uptake and may contribute to therapy-resistant chronic infections.