The susceptibility of <i>Y. enterocolitica</i> O:9 strains with and without protein Ail to normal human serum.

<p>Strains Ye9 (wt), Ye12 (Ye9 Ail⁻), AR4 (OmpR⁻) and AR7 (AR4 Ail⁻) 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 three independent experiments. The asterisks indicate statistically significant differences between Ye9 and AR4 and their isogenic <i>ail</i> mutant Ye12 (Ail⁻) and AR7 (Ail⁻) (* P<0.001, ** P<0.0001, by one way ANOVA with Tukey's comparison post-test).