Chondrocyte Invasion May Be a Mechanism for Persistent Staphylococcus Aureus Infection In Vitro

Area of Science:

• Microbiology
• Cell Biology
• Infectious Diseases

Background:

• Recurrent Staphylococcus aureus bone and joint infections are common.
• S. aureus is known to invade osteoblasts and fibroblasts, but its interaction with chondrocytes is less understood.
• Intracellular persistence within chondrocytes could present a therapeutic challenge.

Purpose of the Study:

• To investigate whether Staphylococcus aureus can infiltrate and persist intracellularly within human chondrocytes in vitro.
• To compare the invasion and persistence capabilities of S. aureus in chondrocytes against osteoblasts and fibroblasts.

Main Methods:

• Human chondrocytes (C20A4), osteoblasts (MG63), and mouse fibroblasts (NIH3T3) were cultured in vitro and infected with S. aureus.
• Cells were treated with antibiotics to eliminate extracellular bacteria.
• Intracellular S. aureus levels were quantified using colony-forming units (CFUs) at various time points post-infection (up to 6 days).

Main Results:

• S. aureus demonstrated significantly higher invasion levels in human chondrocytes compared to osteoblasts and fibroblasts.
• Intracellular S. aureus persisted in chondrocytes for up to 6 days, at levels greater than those observed in osteoblasts and fibroblasts.
• Extracellular antibiotic treatment effectively eliminated S. aureus from the cell media, confirming intracellular persistence.

Conclusions:

• Staphylococcus aureus readily invades and persists intracellularly within human chondrocytes in vitro, evading extracellular antibiotics.
• Chondrocytes exhibit a greater capacity for S. aureus invasion and intracellular persistence than osteoblasts and fibroblasts.
• This chondrocyte-specific mechanism may play a role in recurrent bone and joint infections, warranting further in vivo investigation.