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SUMMARY: The use of mechanical air filtration combined with ultra-violet irradiation of the filtered air has aided markedly in avoiding contamination by undesirable micro-organisms during pilot-plant scale work on penicillin production. By maintaining master cultures of Penicillium strains in sterile soil it has been found possible to eliminate strain variation and to maintain the penicillin-producing capacity of the strains. This procedure, followed by transfer of the organism to a rye grain substrate, gives a convenient method of securing large numbers of spores for large-scale work.
It has been found to be desirable to check the purity of the strains, their penicillin-producing capacity and the viability of the spores at various stages of the production sequence; methods have been developed for each of these requirements. Improvements in the cup assay method of estimating penicillin have eliminated certain difficulties encountered in this assay and have enabled the overall error of the method to be reduced to 5%. A colorimetric method of assay has been developed which gives results agreeing with those of the cup assay. With this new method the penicillin content of a sample can be estimated in 5 hr.