808 XIV. NT'TRTTTONAL VALTTE OF FATS 



bacterial effect of saturated fatty acids was most pronounced in the case 

 of myristic (Ch) and palmitic (Cie), while stearic acid (Cig) had a some- 

 what less notable action, and lauric acid (C12) was less inhibitory. The 

 acids with one to five carbon atoms had little or no growth-inhibitory 

 effects. Chaulmoogric acid, which is an unsaturated, straight-chain C13 

 acid, had the same effect as did myristic acid. In a later report, 

 Drea^-* stated that octyl, decyl, undecyl, dodecyl, and tetradecyl-chain 

 resorcinols inhibited the growth of human tubercle bacilli (strain H 37) 

 to a greater extent than did the corresponding fatty acids or resorcinol 

 itself. Tetradecyl resorcinol had the same effect as did myristic acid in 

 inhibiting growth. 



Dubos^-^ confirmed the fact that long-chain fatty acids exert a toxic 

 effect upon a number of microorganisms, especially the Gram-positive and 

 acid-fast species, and that their toxicity for the bacteria is directly related 

 to the number of unsaturated bonds in the molecule. All the fatty acids 

 tested (capric, lauric, myristic, palmitic, stearic, oleic, ricinoleic, linoleic, 

 linolenic, arachidonic) exerted a bacteriostatic and bactericidal effect on 

 micrococci and on tubercle bacilli in protein-free media. Stearic acid 

 was the least toxic, whereas the unsaturated oleic, ricinoleic, linoleic, 

 linolenic, and arachidonic acids had the greatest bacteriostatic and bac- 

 tericidal action. Human tubercle bacilli were the most sensitive of the 

 organisms tested. Inhibition of growth of small inocula of these organisms 

 in synthetic media could be detected in concentrations of 0.00001 to 

 0.0001% of the fatty acids. Avian tubercle bacilli were ten times less 

 sensitive, and the Micrococcus spp. culture was much more resistant. 

 None of the esters was significantly toxic for Micrococcus cultures. The 

 water-soluble esters of lauric acid and of palmitic acid (Tween 20 (poh^- 

 oxyethylene sorbitan monolaurate) , G 2144, and Tween 40 (poly oxye thy 1- 

 ene sorbitan monopalmitate)) exhibited appreciable bacteriostatic and 

 bactericidal activity against tubercle bacilli in concentrations of 0.01 to 

 0.001%, but esters of stearic and oleic acid (Tween 60 (polyoxyethylene 

 sorbitan monostearate) and Tween 80 (PSM, polyoxyethylene sorbitan 

 monooleate)) were inhibitory only m higher concentrations. In all cases 

 the toxicity was decreased or abolished by the addition of crystalline serum 

 albumin (0.1 to 0.5%), blood plasma, or glucose. Oleic acid acted as a 

 growth factor for Corynebacterium diphtheriae and for Clostridium tetani 

 in concentrations of 1 to 50 A«g. 'ml. of medium. Metabolic studies showed 



"4 W. F. Drea, /. BacterioL, 61, 507-511 (1946). 

 '« R. J. Dubos, J. Exptl. Med., 85, 9-22 (1947). 



