Factors affecting survival of Pseudomonas cepacia in decongestant nasal sprays containing thimerosal as preservative

Strains of Pseudomonas cepacia, isolated from packages of nasal spray preserved with thimerosal, showed a high degree of resistance to the organomercurial, as compared to low and moderate resistance of standard laboratory strains or isolates from water. The product isolates were shown to degrade the thimerosal to metallic mercury which volatilized from the product or assay medium. The addition of organic nutrient was essential for survival of unadapted cells in the product. However, when cells were first grown in diluted product containing added nutrient and then inoculated into the full-strength product, survival and growth occurred even in the absence of added nutrient. The time required for growth to occur was inversely related to the amount of added nutrient. At low nutrient concentrations, approximately 99.9% of the inoculated cells were killed rapidly, but after a lag time of 7-12 days, the few survivors began to increase in numbers and eventually attained high cell concentrations. These findings should be useful in planning production and testing programs with thimerosal-preserved products.