The comparison of susceptibility to endogenous pseudomonas aeruginosa septicemia between endotoxin responder and non-responder mice

Pseudomonas free specific pathogen free (SPF) mice were orally inoculated with Pseudomonas aeruginosa D-4m strain via drinking a 0.45% NaCl solution containing P. aeruginosa. The animals also received ampicillin (ABPC) to promote indigenous colonization. The Pseudomonas colonized mice, rendered neutropenic by cyclophosphamide injection, developed fatal P. aeruginosa bacteremia. Using this model, a comparison of mortality due to P. aeruginosa endogenous septicemia was made between C3H/HeN (endotoxin-sensitive) and C3H/HeJ (endotoxin-resistant) mice. C3H/HeJ mice were hypersusceptible to P. aeruginosa endogenous septicemia, while C3H/HeN mice were resistant. P. aeruginosa levels in the livers were high enough to cause death in C3H/HeJ mice, while the bacteria were eliminated from the livers of C3H/HeN mice. When both strains of mice were also inoculated with P. aeruginosa intravenously, the 50% lethal doses (LD₅₀) of P. aeruginosa D-4m strain were 10^2.4 and 10^2.8 CPU/mouse in C3H/HeJ and C3H/HeN mice, respectively. The clearance rate of P. aeruginosa from blood was similar in the two groups of mice. These results suggest an important difference between endotoxin-sensitive and -resistant mice in endogenous infection.