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Updated: Aug 18, 2026

Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis
Published on: February 6, 2021
Pathogenesis of Staphylococcus in the rabbit anterior chamber
Dalia O Girgis1, Julian M Reed, Kathryn S Monds
1Department of Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
Purpose:
To investigate the host defense against Staphylococcus in the rabbit anterior chamber.
Methods:
The bactericidal activity of rabbit aqueous humor was investigated in vitro. Rabbit anterior chambers were injected with viable Staphylococcus aureus or Staphylococcus epidermidis (1,000 or 500,000 colony-forming units [CFU]), killed bacteria, culture supernatants of either organism, or purified S. aureus alpha-toxin. CFU as well as phospholipase (PLA(2)) and myeloperoxidase (MPO) activities of aqueous humor were determined up to 25 hours postinfection (PI).
Results:
The number of viable S. aureus or S. epidermidis was significantly reduced when incubated with aqueous humor for 30 minutes (P = 0.0001). Rabbits challenged with either S. aureus or S. epidermidis demonstrated a significant reduction in CFU in aqueous humor by 1 hour PI (P = 0.0044). Eyes infected with either S. aureus or S. epidermidis demonstrated a significant increase in MPO activity beginning at 1 hour PI (P = 0.0455), but only S. aureus caused an increase in PLA(2) activity at 20 and 25 hours PI (P = 0.0002). No significant increases in PLA(2) activity were observed after injection of killed bacteria into the aqueous humor at any time point; however, injection of S. aureus supernatant or alpha-toxin into the anterior chamber significantly increased PLA(2) activity (P = 0.0210). Injection of alpha-toxin also resulted in significant increases in MPO activity beginning at 10 hours after injection (P = 0.001).
Conclusions:
This study demonstrates that aqueous humor has a potent host defense capability and that S. aureus, but not S. epidermidis, triggers a PLA(2) response in the rabbit anterior chamber that appears to be due to alpha-toxin.
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