EFFECTS ON THE GROWTH OF MICROORGANISMS 975 



p-MB giving a much higher accumulation. It is more difficult to determine 

 the distribution of Hg++ within the cells. Siipfle (1923) treated anthrax 

 bacilli with Hg++ and then with HgS, and showed black granules within the 

 cells. However, the Hg++ enters much more slowly than the antibacterial 

 action develops, which might be used as evidence for a primary membrane 

 site. Ruska (1947) examined Hg++-treated streptococci and E. coli with 

 the electron microscope and observed mercury in the membrane and dif- 

 fusely distributed in the cytoplasm, but most in small globular masses be- 

 tween the membrane and the cytoplasm. By a similar technique, Harris 

 et al. (1954) found no mercury in the membrane or cell wall of E. coli — 

 confirming the absence of electrophoretic change in cells treated with Hg++ 

 — and most deposited as granules within the cytoplasm. Troger (1959) 

 localized mercury by the diphenylcarbazone method and found accumula- 

 tion in certain areas. It should be noted that visualization either electron 

 microscopically or histochemically is difficult in bacteria and, furthermore, 

 that generally quite high concentrations have been used so that the pattern 

 of distribution cannot apply directly to the bacteriostatic situation. 



The possible mechanisms for the bacteriostatic action of the mercurials 

 have been debated for years and many theories have been proposed without 

 benefit of experimental evidence. The amount of valuable work on the mer- 

 curials from the standpoint of basic actions is almost negligible, due prob- 

 ably to the fact that when bacterial metabolism and proliferation began 

 to be investigated seriously, attention was turned to the sulfonamides and 

 antibiotics. From Tables 7-13 and 7-17 one might conclude that metabolism 

 must certainly be depressed in some manner during the action of the mer- 

 curials on bacteria, and this may well be in many cases, but Yamada and 

 Yanagita (1957) showed quite conclusively that the growth of staphylococci 

 is 140 times and 57 times more sensitive than respiration to thimerosal and 

 Hg++, respectively. Indeed, it is possible to stop growth essentially com- 

 pletely without affecting respiration significantly. Despite the lack of critical 

 experiments in other organisms, it is safe to say that the mercurials do not 

 inhibit the growth of microorganisms by simply suppressing oxidative proc- 

 esses and the supply of energy for growth and division. Fildes (1940) on 

 the basis of irrelevant evidence concluded that the antibacterial mechanism 

 is based on reaction with SH groups, and the impression is gained that he 

 was thinking of the smaller thiols rather than proteins and enzymes. Lou- 

 reiro and Lito (1946) put this theory on a better basis by demonstrating 

 some correlation between the fraction of bacterial SH groups reacted and 

 the bactericidal activity. However, even here all one can do is to increase 

 the mercurial concentration so that more and more SH groups are reacted, 

 and it is not surprising that more and more cells are inhibited or killed; 

 one cannot say what fraction of SH groups should be reacted before an 

 effect on the bacteria is observed, and indeed it is very unlikely that it 



