cdGMP inhibits F. novicida intramacrophage replication. F. novicida strains U112 (WT), KKF457 [ΔFTN(0451–0456)], and KKF539 (cdgA cdgB), either without a plasmid or carrying plasmid pKEK1524 (cdgB) or pKEK1525 (VCA0956), were inoculated at an MOI of ∼10:1 into J774 cells, and intracellular bacteria were enumerated at 1, 24, and 48 h (see Materials and Methods for further details). The assay was performed in triplicate. *, P < 0.0005.