Effect of calcium chloride on experimental infection of mice with Pseudomonas aeruginosa.

Concomitant administration of Pseudomonas aeruginosa and calcium chloride to mice enhanced the virulence of some strains. The 50% lethal dose of P. aeruginosa 5 decreased by more than three orders of magnitude, regardless of the challenge route (intramuscular, subcutaneous, and intraperitoneal injection), while the 50% lethal dose of strain N10 did not decrease. When challenged intramuscularly with 10(4) organisms of strain 5 or strain N10 mixed with calcium chloride, both strains multiplied at the local site of injection. Strain 5 subsequently caused systemic infection, while strain N10 did not. The virulence-enhancing effect of calcium chloride can be successfully applied in protection assays for immunized mice challenged with strain 5.