Age-related changes in the persistence and pathogenicity of Salmonella typhimurium in chicks.

Effects of age at exposure on the persistence of Salmonella in various tissues of chicks were assessed in two experiments. Broiler chicks, housed on wire floors in isolation cabinets, were orally inoculated with S. typhimurium at various ages (1 to 8 days after hatching). The postinoculation mortality of chicks declined significantly (P less than .05) as the age at inoculation increased. One experiment investigated the effect of age at inoculation on the persistence of S. typhimurium in the cecum. Salmonella persisted for 7 wk after inoculation in 81.3% of the chicks inoculated at 1 day of age and in 62.5% of the chicks inoculated at 8 days of age. The mean number of cecal Salmonella at 7 wk postinoculation was also greater for chicks inoculated on Day 1 than for those inoculated on Day 8. The second experiment examined the effect of age at inoculation on the adherence of S. typhimurium to and penetration through the cecal epithelium. The ceca of chicks inoculated at 1 day of age were colonized by significantly more adhering Salmonella at 2 days postinoculation (1.4 x 10(8)/g) than were those of chicks inoculated at 3, 5, or 7 days of age (8.0 x 16(6)/g or less), but age did not affect the recovery of S. typhimurium from livers or spleens.