TF and susceptibility to pneumonia measurement: Indeed, when either i) the 37-CE is deleted (Δ37-CE), ii) one TF’s ability to bind the 37/21-CE is abolished, increasing the affinity of the other (SpxR-only and CpsR-only), or iii) the two TFs are independently deleted (ΔspxR and ΔcpsR), orders of magnitude reductions in CFUs and/or a concomitant increase in host survival were observed during pneumonia.