Daniel Price1, Brandi Eason1, and Donald G. Ahearn2. (1) Microbiology, Interface Research Corporation, 1603 Executive Drive, Lagrange, GA 30240, (2) Biology, Georgia State University, 24 Peachtree Center Ave, Atlanta, GA 30303
Skin care formulations were evaluated for their ability to inhibit spoilage moulds over a 28 day period. Uniform amounts of each formulation were placed into the ring indentions in the lid of 12 well microtiter plates. Sterile nylon membranes were placed onto multiple wells with each formulation and inoculated with conidia suspensions of Paecilomyces variotii, Aspergillus niger, and Penicillium chrysogenum. Membranes were examined (gross and microscopic) at least biweekly for the presence of mould growth and representatives of the replicate set transferred to Letheen neutralizing agar. Mould growth status under controlled humidity prior to and after membrane transfer allowed for the discernment of static versus presumed biocidal activity of the formulations. One of three formulations demonstrated biocidal activity for each of the challenge moulds. Another formulation was inhibitory for all of the challenge moulds while they were in contact with the product, but growth occurred when the membranes were transferred to the neutralizing agar. Inoculated membranes in direct contact with the third formulation developed growth of P. variotii by day three and heavy growth by day seven. Penicillium chrysogenum was the most sensitive to the preservative systems in all of the formulations while Paecilomyces variotii was the most resistant. The modified membrane-transfer procedure may be used as a predictive screen to judge the preservative stability of various products during periods of extended use or environmental exposure.
