Polyamine biosynthesis is not required for fitness in serum ex vivo.
50% naive mouse serum was inoculated with 1x106 CFU wild-type P. mirabilis, an isogenic mutant, or a 1:1 mixture of wild-type P. mirabilis and isogenic mutant (co-culture). The following mutants that exhibited significant fitness defects in the liver and/or spleen during bacteremia were included: speA (A), speB (C), and potB (E). Cultures were incubated statically at 37°C with 5% CO2 and sampled at 0, 1, 3, 6, and 24 hours for enumeration of CFUs on LB agar with and without kanamycin. Error bars represent the mean ± standard deviation from three biological replicates. (B, D, F) A competitive index (CI) was calculated for the mutant at each time point from the ratio of mutant to wild-type colonization level at the time indicated divided by the ratio of mutant to wild-type at time zero (see Materials and Methods). Each data point represents the CI from an individual replicate. Solid lines represent the median. Dashed lines indicate a competitive index of 1, or a 1:1 ratio of mutant to wild-type. Error bars represent the mean ± standard deviation from two or three biological replicates.