FIG. 1.

Systemic virulence of serovar Choleraesuis (SCS) A50, relative to that of serovar Typhimurium (STm) 4/74, in pigs is not associated with enhanced intestinal invasion or enteritis. Panel A shows the magnitude of intestinal invasion by strains of S. enterica serovars Choleraesuis and Typhimurium 3 h after inoculation of porcine distal ileal loops, with the data representing the mean of triplicate determinations in two pigs ± the standard error of the mean (SEM). The dotted line represents the limit of accurate bacterial quantification. The magnitudes of secretory and inflammatory responses induced by the strains 12 h after inoculation of porcine mid-ileal loops are shown in panels B and C, respectively. Data in panels B and C represent the means of triplicate determinations in two pigs ± the standard errors of the means. The secretory response is reported as the ratio of the volume of fluid accumulated (V, ml) to the loop length (L, cm). Neutrophil influx is the ratio of the total gamma radiation emitted from ¹¹¹In-labeled neutrophils from test loops to that emitted from control loops. *, P < 0.05.