FIG 2.

The periplasmic nitrate reductase NapABC provides a fitness advantage during competitive infection. (A) Mice were infected with mixtures of the indicated S. Typhimurium strains in equal amounts. Four days after infection, mice were euthanized, and the competitive index (output ratio over input ratio) was determined in colon contents. *, P < 0.05; **, P < 0.01; ns, not statistically significantly different; wt, the wild-type strain CAL128; napA, the napA mutant CAL277; narG, the narG mutant CAL65; narZ, the narZ mutant CAL315. (B) Nos2 mRNA levels in colonic tissues from the animals used in the experiment for which results are shown in panel A and in control animals treated with streptomycin and inoculated 1 day later with a sterile medium. (C) Mice were infected with a mixture of a napA mutant and a narG mutant in equal amounts. Four days after infection, mice were euthanized, and the CFU counts of both strains in colon contents were determined.