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CITROBACTER RODENTIUM INFECTION IN NEONATAL MICE CAUSES DEATH: PROTECTION BY PROBIOTICS IS MEDIATED BY ADAPTIVE IMMUNITY
M Gareau1, E Wine1, C Reardon2, M Perdue3, P Sherman1
1Hospital for Sick Children, University of Toronto; 2Princess Margaret Hospital, Toronto; 3McMaster University, Hamilton, Ontario
Aims: Citrobacter rodentium is a naturally occurring, non-invasive, murine enteric pathogen that shares many features with pathogenic E. coli species, including enterohemorrhagic E. coli (EHEC), a bacterium linked to food- and waterborne outbreaks. Colonic responses to infection with C. rodentium are similar to those found in patients with chronic inflammatory bowel diseases (IBD). Consequently, C. rodentium is commonly used as a model for both acute, infectious colitis and IBD. Probiotics are live organisms which elicit beneficial effects, but further research is needed to establish their efficacy in newborns and infants. This study employed C. rodentium challenge of mouse pups to determine the effects of infection in neonates and assess whether probiotics could reduce disease burden. We hypothesized that neonatal pups would become ill following infection with C. rodentium and that probiotics would ameliorate disease severity.
Methods: C57BL/6 mouse pups were infected with C. rodentium (108 CFU in 0.05 ml LB broth) or sham-infected (LB broth) by orogastric gavage on post-natal day 14. A subset of pups were pre-treated with a mixture of Lactobacillus helveticus R0052 and L. rhamnosus R0011 (108 CFU orally) once daily one week prior to infection and continued for the duration of the experiment. Maltodextrin served as the vehicle control. To determine if probiotics could act indirectly, the probiotic mixture was provided to the dam directly in drinking water. Neonatal Rag1 deficient (Rag1-KO) pups were used to determine the role of adaptive immunity in mediating the effects of probiotics.
Results: At 10 days post-infection (PI), infected pups exhibited significant weight loss and colonic epithelial cell hyperplasia compared to sham-infected pups. By 12 days PI, death occurred only in infected animals (C. rodentium; 75% mortality versus sham; 0%). Pre-treatment with probiotics significantly reduced mortality (C. rodentium; 75% mortality compared with probiotics; 17%, p<0.05), colonic epithelial cell hyperplasia, and attenuated weight loss. Probiotics did not prevent death in infected pups when administered either to the mother or in Rag1-KO pups.
Conclusions: C. rodentium infection causes severe colonic inflammation resulting in weight loss and death in neonatal mice. Pre- and co-treatment with probiotics to the pups prevents these effects, but only when provided directly and in immune competent animals. Therefore, probiotics could prove an important therapeutic option for use in the management of newborns at high risk for developing intestinal infections and inflammatory disorders, including those cared for in the neonatal intensive care unit.