ANTIMICROBIAL ACTIVITY 633 



is clear that fungi are more sensitive to dehydroacetate than are bacteria. 

 The means of the concentrations in the table are, of course, not quantita- 

 tively significant, but show well the difference: 26 mM for bacteria and 

 1.1 mM for fungi. The mechanism of growth inhibition is completely un- 

 known. There is no obvious correlation between cycle activity in these organ- 

 isms and susceptibility to dehydroacetate. The fungi behave differently than 

 bacteria with regard to so many drugs that one must assume basic differ- 

 ences in metabolism or permeabilities, and it would be impossible at this time 

 to attribute the greater sensitivity to dehydroacetate to any one factor. 

 Permeability seems to be of importance in the action of dehydroacetate, 

 as indicated by the effects of pH. A decrease in activity with increasing pH 

 has been generally noted (Shibasaki and Terui, 1953; Bandelin, 1958), with 

 the exception of Salmonella and Staphylococcus (Wolf and Westveer, 1950). 

 The results of Bandelin on several fungi are typical (see accompanying ta- 

 bulation). A 100- to 200-fold increase in activity as the pH is raised from 



3 to 9 is observed. The only obvious explanation is that the anionic forms 

 of dehydroacetate do not penetrate well. The major decrease in activity 

 occurs between pH 5 and 7, correlating with the pK^'s near 5.2, 



