754 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS infections affecting staff may well lead to localized high levels of atmos- pheric contamination. Apart from the widely varying levels of atmospheric contamination actually present, assay techniques may lead to extremely variable findings depending, for example, on whether they record static or dynamic condi- tions of the air being sampled. For these various reasons, quantitative standards cannot be recommended for general application. It is, however, suggested that atmospheric contamination should be monitored along with other possible sources of contamination, in order to gain a general picture of the microbiological status of a production unit. Suggested methods for use with a slit sampler* are impingement on selective media or membrane filtration after impingement in broth. A suitable range of media would be Nutrient Agar and MacConkey Agar for the isolation of bacteria, Sabouraud and Malt Extract Agar for the isolation of yeasts and fungi. 9,. PRODUCT DEVELOPMENT 9,.11 Assessing preservative capacity Whatever the preliminary methods of evaluating the effectiveness of a preservative, the final test should always be carried out on the complete formulation in the final pack. Most procedures are based on a dynamic or spoilage type of test in which the sample to be tested is challenged by inoculation with a selection of appropriate spoilage organisms. The con- taminated sample is subsequently examined for evidence of microbial activity during a test period usually lasting several weeks or preferably, in the case of moulds, for several months. If micro-organisms fail to grow in such a test, the sample can be re-challenged to provide further information on the stability of the preservative system. 2.12 Challenge organisms The range of micro-organisms examined in preservation tests is logically selected from those usually responsible for spoilage and others associated xvith common infections. Micro-organisms used in preservation studies must be vigorous strains and should include recent isolates from contaminated samples. Along with locally-isolated laboratory and factory contaminants, *A suitable piece of equipment for testing air samples under standard conditions is Airborne Bacteria Sampler Mark II. From: C. F. Casella and Co. Ltd., Regent House, Britannia Walk, London, N. 1.

HYGIENIC MANUFACTURE AND PRESERVATION 755 the following typical spoilage organisms obtainable from Type Culture Collections have been recommended for the testing of preservatives (Appendix E, 2.7, p. 797): Bacteria Staphylococcus aureus, Staph. epidermidis, Micrococcus spp., Streptococcus spp, Corynebacterium pseudodiphtheriticum, Coliform, Coli-Aerogenes group, Proteus, Pseudomonads including Ps. aeruginosa, Bacillus cereus, and B. Subtills. Moulds and yeasts Fungal organisms should include Penicillium, Aspergillus, Mucor, Clado- sporium, Alternaria, Trichoderma viride, Candida and Saccharomyces species. Naturally occurring bacterial contaminants will usually flourish more vigorously in a manufactured product than will the type culture strains of medical importance. It is advisable, therefore, first to inoculate the un- preserved formulation. Only those organisms showing vigorous growth and surviving for more than ten days in the product should be selected for testing preservative effectiveness. The selection of appropriate spoilage organisms and the number of strains to be used in a particular study is obviously important the final choice and method of inoculation is left to the discretion of the microbiologist performing the test. An unpreserved formulation should always be included to serve as control this should be checked for microbial content before commencing preservation studies. Inoculation with bacteria may be carried out with an actively growing broth culture by stirring 0.1 ml of culture into about 30 ml or the equivalent of product. (See also methods 2.121 and 2.122.) A viable count is performed on each suspension to estimate the number of live bacteria which has been mixed into each test sample. Inoculation with moulds and bacteria must be carried out separately. Care must be exercised in the handling of preparations which have been deliberately infected with potentially dangerous micro-organisms. Strains of Pseudomonas aeruginosa recently isolated from clinical infections can be particularly harmful to the eyes and should only be used in preservation studies with great care to avoid disseminating infection. The culture used for test purposes may be grown on solid or in liquid medium a young and actively growing culture is essential. One of the following procedures will normally be applicable.