In vivo internalization of Staphylococcus aureus by embryonic chick osteoblasts

Area of Science:

• Microbiology
• Cell Biology
• Bone Biology

Background:

• Staphylococcus aureus is a primary cause of osteomyelitis, a bone infection.
• Previous studies showed S. aureus can enter osteoblasts in vitro.
• Osteomyelitis is an acute and recurrent bone disease.

Purpose of the Study:

• To demonstrate in vivo the internalization of S. aureus by embryonic chick osteoblasts.
• To investigate the effect of bacterial internalization on osteoblast and osteocyte morphology and differentiation.
• To support the hypothesis that S. aureus internalization contributes to osteomyelitis etiology.

Main Methods:

• Injection of S. aureus (strains UAMS-1 or Cowan 1) into 17-day-old chick embryos via subcutaneous or intraallantoic routes.
• Harvesting of calvariae and tibiae for transmission electron microscopy (TEM) analysis at different time points (45 min and 48 h).
• Quantification of bacterial internalization in osteoblasts and osteocytes and assessment of cellular changes.

Main Results:

• S. aureus was found in approximately 14% of calvarial osteoblasts after subcutaneous injection and 11% after intraallantoic injection.
• Bacteria were observed within endosomes and free in the cytoplasm of osteoblasts; osteocytes also showed intracellular bacteria.
• Osteoblasts with internalized S. aureus exhibited cytoplasmic integrity loss and nuclear changes, yet continued differentiation.

Conclusions:

• Bacterial internalization by osteoblasts and osteocytes occurs in vivo, supporting in vitro observations.
• Internalization of S. aureus by bone cells may play a significant role in the pathogenesis of osteomyelitis.
• Further research is warranted to understand the mechanisms and implications of bacterial invasion in bone infections.