In challenge infections using WT UTI89 and UTI89ΔhlyA strains in naïve, resolved and sensitized mice, we observed that ΔhlyA infection, which does not activate caspase-1-mediated pyroptotic cell death, showed significantly increased bacterial burdens in sensitized mice compared with WT mice, whereas no differences were observed in naïve and resolved mice (Fig. 5g). Here, CASP1 is linked to infection.