GZMB and infection: A comparison of the level of mortality associated with all strains at 1 and 2 dpi showed a hierarchical trend of WT > ΔcspAD (cspB) > ΔcspAB (cspD) > ΔcspBD (cspA) > ΔcspABD; P < 0.05), which was similar to the survival and growth efficiency trends observed using the THP-1 human macrophage cell infection model (Figure 2A).