Total caecal load of S . Enteritidis S1400nalR wild-type, Δ fimA :: cat , Δ steA :: cat and Δ safA :: cat mutant strains at 3, 7 and 10 days post-oral inoculation of 18-day-old out-bred Rhode Island Red chickens. Blue lines with diamonds denote the wild-type strain and pink lines with squares denote the fimbrial mutants. The dashed line indicates the theoretical limit of detection by direct plating (2.2 log10 CFU/g). Samples positive only by enrichment culture were given an arbitrary value of 1 log10 CFU/g since at least one viable organism must have been present. The data reflect the mean ± standard error of the mean from five birds at each time interval. F-tests of the difference in recovery of wild-type and mutant strains at each time interval were performed and P values < 0.05 are marked with an asterisk.