Total caecal load of S . Enteritidis P125109 wild-type and major fimbrial subunit 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). 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.