Development of a Murine Model with Optimal Routes for Bacterial Infection and Treatment, as Determined with Bioluminescent Imaging in C57BL/6 Mice

Mice intragastrically infected with Listeria monocytogenes EGDe and Staphylococcus aureus Xen 36 showed no visible signs of infection over 48 h. However, high numbers (6.2 × 10⁵ cfu/mg feces) of S. aureus Xen 36 were detected 4 h, and 3.3 × 10⁵ cfu/mg feces of L. monocytogenes EGDe 8 h, after administration. Mice intraperitoneally infected with S. aureus Xen 36 (1 × 10⁷ cfu) developed infection immediately after administration and for at least the following 48 h. Injection with higher cell numbers of S. aureus Xen 36 (2 × 10⁸ cfu) resulted in more intense bioluminescence (infection) of the peritoneal cavity. Injection of S. aureus Xen 36 in the tail and penile veins resulted in localized tissue infection for the first 120 h. Injection of S. aureus Xen 36 into the thigh produced a faint bioluminescent signal for 15 min. Nisin F injected into the peritoneal cavity at the same area of infection led to an immediate statistically significant decrease in infection (from 2 × 10⁶ p/s/cm²/sr to 3 × 10⁵ p/s/cm²/sr) within 2 h. Similar results were recorded when nisin F was injected subcutaneously. Intraperitoneal administration is an optimal administration route for bacterial infection and treatment with antimicrobial peptides.