Establishing an experimental Pseudomonas aeruginosa keratitis model in mice - Challenges and solutions.

Background: With the ongoing increase in antimicrobial resistances seen in bacterial isolates causing a keratitis in humans, animal models have become an important tool to study new antimicrobial therapies. Nevertheless, the establishment of experimental keratitis is difficult. Here, we discuss the impact of different arrangements, including animal age, bacterial strain and dose as well as epithelium removal on the outcome of experimental keratitis. We therefore present the methods and results of our establishing experiments.

Methods: Bacterial load determination and flow cytometry were performed using eye homogenate gained from a 72 h lasting murine Pseudomonas aeruginosa keratitis model. Additionally, the intensity of the infection was scored from 0 to 5, the mice weighed, and blood immune cells counted.

Results: We found that older C57BL/6 N mice (8-11 months) are more susceptible to develop a keratitis than younger mice (5-6 weeks). Epithelium removal has no major impact on infectivity and disease progression in aged mice. P. aeruginosa exoU strains, such as PA54, should preferentially be used and highly concentrated (∼ 5 ×10 colony forming units CFU). Establishing an infection with the exoU PAO1 derivative DSM 19880 was not possible.

Conclusions: We present a replicable method to achieve a successful experimental P. aeruginosa keratitis in C57BL/6 N mice that is sustained or aggravated over the observation period of 3 days in 80 % of all animals tested. Our work is of particular interest to all researchers planning the establishment of such experimental models. We show some key aspects that can simplify and quicken the procedure, ultimately saving costs and animal life.