To Örebro University

Background and Significance: Vaccine studies for Chlamydia trachomatis (Ct) have been hampered by the lack of an ideal murine model. Ct is not ideal for infection and subsequent pathology as it is a human pathogen and C. muridarum (Cm) may not be suitable due to vaccine specificity for Ct. There is currently no standardization of chlamydial infections in murine models concerning mouse strain, infecting agent and dose.

Objectives: To investigate the Ct infection in mice, using different suppliers of mice, doses and the infective agents of Ct serovars D, E and Cm.

Methods: C57BL/6 mice (Taconic; Harlan; in-house breeding mice) were inoculated intravaginally with 10³-10⁵ chlamydia  elementary bodies (EB). Vaginal samples were collected at 7-8 days intervals and analyzed using MicroTrak II Chlamydia EIA kit.

Results: Taconic mice inoculated with Ct D with 10⁵ EB showed the strongest infection with 30% of mice infected at day 21 (d21) as seen in figure 1. The number of infected mice and detected antigen (not shown) decreased rapidly after the first time-point (d8). In figure 2 infective agents were analyzed. Ct E did not infect any mice despite using a tenfold increased dose. Cm infection was detectable in 80% of the mice for up to d21.

Conclusions: Ct D infected the mice for a period of 2-3 weeks. There was only a small difference between the suppliers in favor for Harlan mice. Ct D 10⁵ EB was the infectious dose with the highest number of infected mice over time, however the appropriateness of that high bacterial load must be considered. Ct E did not infect these mice and Cm, a mouse pneumonitis strain, infected all mice and had the longest duration of infection. However, for vaccine studies, Cm may not be suitable due to lack of cross reactivity and Ct may still be used however vaginal sampling must be more frequent early on to show significant differences in bacterial shedding between immunized and non-immunized mice.