Dose response curve for the ELA. The ELA was performed with Y. enterocolitica 8081v and 8081c strains and E. coli A4 and V1 strains as controls. Undiluted Y. enterocolitica cultures contained 2 × 109 CFU/ml and serial dilutions were performed in steps of 1:10. Bacterial cultures (100 μl) were administered to the chicken embryos into the allantoic fluid and lethality of the embryos was determined for five consecutive days (Panel A). The experiment was done twice, the mean of the average is presented. Standard deviations varied between 5 and 30%. Panel C is the dose response curve for the two Y. enterocolitica strains between inocula of 1 × 105 and 1 × 109 CFU after five days. Data are expressed as the mean over the two experiments and error bars indicate 1 s.