Effects of challenge dose on crop colonization of Salmonella Enteritidis in experimentally infected chickens

Salmonella enterica, subspecies enterica serovar Enteritidis (S. Enteritidis), is Currently the main serovar causing frequent human illness associated with egg contamination. This study was conducted to determine the effects of a challenge dose of S. Enteritidis on crop colonization in experimentally infected chickens. Twenty-four specific-pathogen-free hens were divided into three groups of eight. The first and second groups were orally challenged with a dose of 1.3 x 10(8) and 1.3 x 10(4) colony forming units (cfu) of S. Enteritidis per hen respectively. The third group comprised uninfected controls. Crop lavage samples were collected weekly for 5 weeks and cultured for the presence of S. Enteritidis. Salmonella Enteritidis was isolated from the samples for 5 weeks and one week post-infection, from hens infected with 10(8) cfu/mL and 10(4) cfu/mL of S. Enteritidis respectively. Levels of S. Enteritidis recovered from the crops of hens infected with a dose of 10(8) cfu/mL were significantly higher (P<0.05) than from those infected with 101 cfu/mL. At week I post-infection, organisms recovered from the 10(8) cfu/mL group were greater than 4 logs and significantly higher (P<0.05) than in the 101 cfu/mL group. The rate of crop colonization of hens infected with 10(8) cfu/mL, S. Enteritidis dropped from 100.0% to 62.5% and 25.0% at weeks 1, 3 and 5 post-infection respectively. Since the amount of organism colonizing a tissue is proportional to the level of antibodies produced, to ensure the protection of vaccinated chickens, Salmonella vaccines should contain an adequate vaccine dose.