Figure 3. The susceptibility of Y. enterocolitica O:9 strains lacking YadA protein to normal human serum.

Strains Ye9 (wt) and AR4 (ompR) harboring the virulence plasmid pYV (yadA ⁺) and their plasmid-cured derivatives (Ye9c and AR4c, respectively) were grown to exponential phase at 37°C and incubated with 50% NHS at 37°C. Aliquots removed at 0, 15, 30 and 60 min were plated for viability counts (CFU). The numbers of CFU/ml were normalized to the T₀ values as a percentage and then converted to log₁₀ to show the survival rate of the bacteria in NHS. Data are the means ±SD from at least three independent experiments. The Ye9c, pYV⁻ and the AR4c, pYV⁻ asterisks indicate statistically significant difference in comparison with the strains carrying pYV (Ye9 and AR4) (* P<0.001, ** P<0.0001, by one way ANOVA with Tukey's comparison post-test), n.s. not significant.