Binding of a Staphylococcus aureus bone pathogen to type I collagen

Area of Science:

• Microbiology
• Biochemistry
• Orthopedics

Background:

• Staphylococcus aureus is a common cause of osteomyelitis, a bone infection.
• The interaction between S. aureus and bone extracellular matrix components is crucial for pathogenesis.
• Collagen is a major protein in the bone extracellular matrix.

Purpose of the Study:

• To investigate the collagen-binding potential of Staphylococcus aureus strain SMH, an experimental osteomyelitis pathogen.
• To compare the collagen-binding ability of strain SMH with other S. aureus strains, including capsular variants.
• To identify factors influencing collagen binding, such as bacterial surface components and specific inhibitors.

Main Methods:

• Utilized an iodine-125 (125I)-collagen binding assay to quantify binding.
• Tested formalin-killed S. aureus SMH and various other strains, including capsular variants.
• Assessed the effect of different sugars and amino acids on collagen binding, and the impact of trypsinization and encapsulation.

Main Results:

• S. aureus strain SMH exhibited strong binding to type I collagen (Kd = 2 x 10(-9) M), comparable to the known binder Cowan 1.
• Binding was saturable and not significantly inhibited by most tested sugars and amino acids, except for moderate inhibition by D-lactose and strong inhibition by L-fucose.
• Encapsulated strains showed reduced or no avid collagen binding, while capsule-negative variants (e.g., Smith compact) displayed extensive binding, suggesting capsules interfere with collagen interaction.

Conclusions:

• The prototype bone pathogen S. aureus binds to type I collagen, a key component of the bone extracellular matrix.
• Collagen binding is primarily mediated by protein adhesins on the bacterial surface, not the capsule.
• Bacterial encapsulation appears to hinder, rather than promote, collagen binding in S. aureus.