Induction of a homologous and heterologous invasion-inhibition effect after administration of Salmonella strains to newly hatched chicks.

Administration of live Salmonella strains to day-old chicks provides protection against infection within hours by intestinal colonisation-inhibition. However, the extent to which the oral application of live Salmonella wild-type or vaccine strains may induce an early invasion-inhibition effect is unknown. Potentially protective pre-treatment strains of Salmonella Enteritidis and Infantis were examined for their ability (i) to colonise the caeca, to invade the liver, to induce an influx of granulocytes in caecal mucosa and, (ii) for their capacity to inhibit the systemic invasion of homologous and heterologous Salmonella challenge organisms. The highly invasive strain Salmonella Enteritidis induced a strong influx of heterophils in the caecal mucosa followed by a complete invasion-inhibition of both homologous and heterologous Salmonella challenge organisms administered 24h later. Pre-treatment with a less invasive Salmonella Infantis resulted in a lower influx of granulocytes in the caecal tissue followed by a complete invasion-inhibition of the homologous serovar Infantis but only an incomplete invasion-inhibition of heterologous serovars. This invasion-inhibition effect has not been described previously in chickens and should be considered in the development of novel live Salmonella vaccines to prevent an early invasion of extra-intestinal organs by Salmonella challenge organisms in young chicks.