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j. Soc. Cosmet, Chem,, 36, 413-423 (November/December 1985) Resistance of Pseudomonas strains to imidazolidinyl urea PATRICIA I. BOWMAN and SUSAN M. LINDSTROM, Avon Products, I.c., Suffer., NY 10901. Received August 21, 1985. Presented at the Annual Scientific Seminar of the Society of Cosmetic Chemists, May 1985, St. Louis, MO. Synopsis Five strains of Pseudomonas, isolated from cosmetic products, demonstrated resistance to high concentrations of imidazolidinyl urea. The resistance of the organisms to various concentrations of the preservative was tested by dissolving the compound in 0.1% nutrient broth. After a 24-hour lag period, all product isolates survived and grew in at least 2.0% imidazolidinyl urea. Two strains grew well in 6% imidazolidinyl urea. Similar growth patterns were demonstrated in simple oil-in-water emulsions, preserved with imidazoli- dinyl urea. The addition of the emulsion only slightly enhanced the growth of the organisms in the presence of imidazolidinyl urea. Pre-incubation of the organisms in broth or the emulsion containing the preservative eliminated the 24-48 hour lag phase before growth occurred. The non-resistant strain, Pseu- domonas aeruginosa ATCC 9027, could not be adapted to grow in the presence of the preservative. After 21 days of incubation, the imidazolidinyl urea content of the broth inoculated with the resistant strains decreased by at least 80%. The decrease of imidazolidinyl urea in inoculated broth was chemically deter- mined through a spectrophotometric assay after degrading the imidazolidinyl urea to formaldehyde and converting the formaldehyde to a UV-absorbing lutidine derivative. It is hypothesized that the resistant organisms are able to metabolize or chemically bind imidazolidinyl urea. INTRODUCTION It has been well documented that Pseudomonas species are able to develop resistance to antimicrobials either by natural selection or mutation. For example, Pseudomonas has demonstrated resistance to quaternary ammonium compounds (1), p-hydroxybenzoic acid esters (2) mercurials (3,4), and iodophors (5). Orth and Lutes (6) and Borovian (7) demonstrated the adaptability of P. aeruginosa and P. cepacia to several commonly used cosmetic preservatives. Pseudomonas species continue to be encountered as contaminants in cosmetic products (8). Therefore, it is imperative that cosmetic preservatives demon- strate activity against these ubiquitous organisms. One cosmetic preservative, ranked by the FDA as the third most frequently used, is imidazolidinyl urea (9). This broad spectrum compound has been shown to be effective against several types of microorga- nisms, including Pseudomonads (10, 11). However, in this laboratory we have encoun- tered strains of Pseudomonas which survive and grow in cosmetic formulations preserved with imidazolidinyl urea. Examination of an isolate resistant to imidazolidinyl urea began in this laboratory during the development cycle of a moisturizer preserved with imidazolidinyl urea (0.3%) and methyl paraben (0.3%). A challenge test organism, Pseudomonas aeruginosa, was recovered from the product after eight weeks of incubation. The organism had not 413