The colonization, translocation and protective effect of two intestinal bacteria - PR4 (pig commensal strain of Bifidobacterium choerinum) or
EcN (probiotic Escherichia coli strain Nissle 1917) - against subsequent
infection with a virulent LT2 strain of Salmonella enterica serovar Typhimurium were studied in gnotobiotic pigs after oral association. The clinical state of experimental animals correlated with bacterial translocation and levels of inflammatory
cytokines [a
chemokine,
interleukin (IL)-8, a proinflammatory
cytokine, tumour
necrosis factor (TNF)-α and an anti-inflammatory
cytokine, IL-10] in plasma and intestinal lavages. Gnotobiotic pigs orally mono-associated with either PR4 or
EcN thrived, and bacteria were not found in their blood. No significant inflammatory
cytokine response was observed. Mono-association with Salmonella caused devastating septicaemia characterized by high levels of
IL-10 and TNF-α in plasma and TNF-α in the intestine. Di-associated gnotobiotic pigs were given PR4 or
EcN for 24 h. Subsequently, they were infected orally with Salmonella and euthanized 24 h later. Pigs associated with bifidobacteria before
Salmonella infection suffered from severe systemic
infection and mounted similar
cytokine responses as pigs infected with Salmonella alone. In contrast,
EcN interfered with translocation of Salmonella into mesenteric lymph nodes and systemic circulation. Pigs pre-associated with
EcN thrived and their clinical condition correlated with the absence of
IL-10 in their plasma and a decrease of TNF-α in plasma and ileum.