Experimental design, body weight, clinical score and survival rate of C57BL/6J mice after lung infection with C. trachomatis serovar D. (A) Mice were intranasally (i.n.) infected with 4 × 10⁶ IFU of C. trachomatis (Ctr) or mock material and subsequently monitored for up to 20 days. The early tetracycline (Tet) treatment (T_E) was applied once a day on days 1–3 after infection. The late tetracycline treatment (T_L) was applied on days 3–5 after infection. In this experiment 20 mg kg⁻¹ tetracycline i.p. were used. Control groups received buffer solution instead (NaCl). Infected early-treated mice and corresponding control animals were euthanized on days 4, 6, 8 and 20 p.i. Infected late-treated and corresponding infected control mice as well as the mock-treated mice were euthanized on day 6 p.i. (B) Body weight loss of the different groups is depicted as means ± standard errors of the means. (C) Clinical score, composed of parameters such as pilo-erection, body posture, locomotion, breathing, dehydration, attention/curiosity and secretion from nose and eyes. Score values are depicted as medians ± interquartile ranges. (D) Comparison of the survival rate of the CtrD/Buffer (early) and CtrD/Tet (early) groups. Asterisks indicate statistical significances: *P = 0.05; **P = 0.01; ***P = 0.001.