Virulence analysis of a Salmonella gallinarum strain by oral inoculation of 20-day-old chickens

SUMMARY. In order to know the effect of in vitro passages on the pathogenicity of the Salmonella gallinarum strain INTA 91, a lyophilized culture was compared with the same strain recently isolated from a sick bird. The mean lethal dose (LD50) of the orally administered lyophilized culture was determined as 2.04 × 108 colony-forming units (CFU)/chicken. There was no correlation between the LD50 dose and the degree of disease produced; doses 10 or 100 times higher than the calculated LD50 did not produce a more severe disease. In trial 1, chickens were challenged with 1.02 × 109 CFU per chicken (5LD50) of the lyophilized strain and reached 52.2% mortality at the end of the assay. In trial 2, three different groups of chickens were infected with a recent isolate of the same strain: 2.04 × 108 CFU/chicken, 4.1 × 108 CFU/chicken, and 2.1 × 109 CFU/chicken (i.e., 1LD50, 2LD50, and 10LD50 of the dose calculated for the lyophilized strain, respectively). These chicken groups presented higher mortality rates (90%...