CHEMOTHERAPY 153 



sulphoiiamide drugs, but not to drugs of different types 

 such as the dyestuffs of the acridine series or the 

 propamidines. It has been found that sulphonamide 

 resistant organisms have acquired the property of in- 

 creased production of ^^-aminobenzoic acid so that their 

 groAvth is no longer inhibited by the drug. 



Strains of hsemolytic streptococci and of C. diphtherice 

 have been produced which are resistant to the action of 

 pantoyltaurine. Some such strains also occur naturally. 

 These strains are sensitive to the sulphonamides, and 

 sulphonamide resistant strains are sensitive to pantoyl- 

 taurine. The varying resistance of naturally resistant 

 strains of C. diphtherice to pantoyltaurine is associated 

 with their ability to convert p -alanine into pantothenic 

 acid, instead of having to be supplied with the latter, 

 which reverses the effect of pantoyltaurine. Mcllwain 

 has shown that this mechanism cannot apply to Sir. 

 pyogenes since many naturally resistant strains and all 

 experimentally produced resistant strains still need to 

 be supplied with pantothenic acid and cannot utilise 

 [3-alanine instead. Resistant strains of Sir. pyogenes and 

 strains of Proteus morganii, Leuconostoc inesenteroides, 

 Lactobacillus and propionic acid bacteria become sus- 

 ceptible to pantoyltaurine when salicylate is added. This 

 is explained on the assumption that salicylate acts on 

 the same groups as does pantoyltaurine, that is on 

 enzymes involved in pantothenic acid metabolism. It 

 should be pointed out that pantothenic acid antagonises 

 the action of salicylate. If this is true, pantoyltaurine 

 resistant strains of Str. pyogenes differ from susceptible 

 strains in having alternative processes for utilising 

 pantothenic acid which are not blocked by pantoyltaurine, 

 although they may still be inhibited by salicA^late. Re- 

 sistant strains of a normalh^ susceptible organism are 

 found occurring naturally and must have arisen by a 

 means other than " training " in tlio presence of tlio 

 drug. A clue to the mechanism by which this can happen 



