FLG and infection: Because both characteristics are important during CDI, we analyzed the virulence of flg RIR mutants in a hamster model of infection, which is particularly sensitive to TcdA and TcdB and manifests acute CDI.19,20,46 Prior work showed that inactivation of genes in the flgB operon, which resulted in reduced toxin production, also attenuated virulence in this model,34,35 so we anticipated that the hamster model would distinguish the virulence of phase-locked flg ON and flg OFF mutants.