Fig. 1

Effect of pre-inoculation of Y. pestis on survival of rats after challenge with a lethal dose of bacteria. Three groups of F1 rats originating from plague-endemic area were first inoculated with 0, 15 or 150 cfu of Y. pestis (strain 40/09B) and followed over 29 days (Tinit = time of initial inoculations). Survivors were then challenged with 15,000 cfu of the same strain and followed over 29 days. Blood samples were collected on day 0, 8, 13 and 21 after both the first and lethal inoculations of Y. pestis. Male/Female repartition was: 0 cfu (7/8); 15 cfu (8/7); 150 cfu (10/5). a Survival data is represented following Kaplan–Meier representation; b Data related to the curve; c Kinetics of anti-F1 IgM and d Kinetics of anti-F1 IgG antibodies from the three groups of F1 rats first inoculated with 0, 15 or 150 cfu of Y. pestis and challenged with 15,000 cfu are presented separately for rats surviving to the challenge (surv) and those that deceased (dcd)