In vivo competition between ∆T6SS
deletion mutant and the wild type Salmonella Dublin strain CT_02021853 in orally infected chicks. Five four-day-old White Leghorn chicks were infected intragastrically by gavage with 109 CFU of a mixture at a 1:1 ratio of the ∆T6SSSPI-6 mutant strain and the wild type Salmonella Dublin CT_02021853. At day 9 post-infection chicks were sacrificed and organs were excised, homogenized, and serially diluted to determine bacterial loads. Bars represent the geometric mean of the log ratio of the mutant CFU/wild type CFU, normalized to the inoculum ratio. Error bars denote standard error. Statistical significance was determined using a two-tailed Student’s t test, and asterisks indicate that normalized output ratios were significantly statistically different from the equivalent ratio in the inoculum (* P < 0.05; ** P < 0.001).