The effect of oral administration of a homologous hilA mutant strain on the long-term colonization and transmission of Salmonella Enteritidis in broiler chickens.

The effect of pre-treatment with a homologous live Salmonella hilA mutant strain on the long-term colonization and transmission of Salmonella Enteritidis in broilers was evaluated. For this purpose, three treatment groups of newly hatched broilers were created. Each group consisted of 4 pens with 25 birds per pen. The first and second groups were orally inoculated with a Salmonella Enteritidis hilA mutant strain (Nal r) whereas the third group was not. In the second and third group, 20% of the birds were challenged 1 day later with a Salmonella Enteritidis wild type strain (Strep r). The Salmonella Enteritidis hilA mutant strain showed no residual virulence in the chicken host and was largely cleared from the chickens at 6 weeks of age. A significant long-term inhibition of faecal shedding and caecal and internal organ colonization of the wild type Salmonella Enteritidis strain was observed in the birds pre-treated with the hilA mutant strain. Although pre-treatment with a hilA mutant strain could not fully prevent the spread of Salmonella Enteritidis amongst the broilers, a significant reduction of transmission was observed in comparison to the non-pre-treated groups. The observed colonization-inhibition (CI) indicates that administration of live attenuated hilA mutant Salmonella strains to newly hatched chicks might, in combination with other protective control measures, contribute to the control of Salmonella infections in broilers.