The Importance of Enrichments in the Cultivation of Bacterial Spores Previously Exposed to Lethal Agencies

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Abstract
Bacterial spores which survive drastic killing influences are much more exacting in their nutritive requirements than the less resistant individuals which comprise the bulk of the viable population before treatment. Heat-surviving Escherichia coli show the same reaction. Enrichment substances incorporated in culture media are essential for the accurate enumeration of bacteria previously exposed to highly lethal factors. The enrichment substances to be used will vary with the species of organism and the nature of the destructive action. The effectiveness of enrichments in the determination of viability varies with the extent of the killing action. The favorable influence of growth-promoting substances increases as the percentage mortality increases and may be negligible in the presence of low mortality. Spores which survive destructive influences when seeded in inadequate media lose their viability rather rapidly.