50 RUSSELL J. BEERS 



The limiting moisture levels for growth of these organisms was also 

 investigated for comparison. The highest concentrations of sucrose which 

 would support growth (increase in optical density in 48 hours) were 45% 

 (94.7% moisture activity) for B. cereus var. terminalis, 46% (94.4% mois- 

 ture activity) for B. subtilis, and 49% (93.7% moisture activity) for B. 

 megatherium. For CI. botulinum, using a trypticase-glucose medium, no 

 growth could be demonstrated above 30% sucrose (97.6% moisture activity) 

 (see Table III). 



Table III 



Moisture Limits for Growth 



Moisture 

 Organism Limit 



B. cereus var. terminalis 94.7 



B. subtilis 94.4 



B. megatherium 93.7 



CI. botulinum 97.6 



Thus, for aerobic species of spore formers at least, higher moisture activi- 

 ties are required for germination than for growth. There appear to be 

 slight species differences in the moisture requirements for germination among 

 the aeobic species, but this is affected by their method of preparation and 

 storage history, and if our idea of multiple stages of germination is correct, 

 this can be verified only when we know for certain that we are dealing with 

 fully dormant spores. 



References 



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Fabian, F. W. 1951. Food Preservation by Use of Microorganisms. In 

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