166 ANTISEPTICS 



ruff (1942) concerning the concentrations required for 

 inhibition of growth of four different organisms. 



Staphylococci and streptococci can be adapted to very 

 high doses of penicillin, 30 times the originally inhibiting 

 concentration for the streptococci, 1000 to 6000 times for 

 the staphylococci (Abraham et al., 1941; McKee and 

 Houck, 1943). In this process of adaptation, increase in 

 tolerance was combined with an almost complete loss 

 of virulence. These projDerties were retained after trans- 

 fer to normal broth, which is contrary to the usual prompt 

 loss of acquired tolerance. The same retention of peni- 

 cillin-resistance has been reported by Schmidt and Sesler 

 (1943) for Pneumococcus Type III. There is no relation 

 between resistance to penicillin and to sulfonamides. 



The disinfectant action of penicillin has been studied 

 by Hobby, Meyer and Chaffee (1942). The order of 

 death of pneumococci, streptococci and staphylococci by 

 50 ppm. of penicillin was logarithmic, at least during the 

 destruction of the first 99% of the cells (Figure 34). The 

 death rate decreased when the size of the inoculum in- 

 creased, w^hicli may be due to the protective action of large 

 numbers of cells. The penicillin concentration was not 

 noticeably decreased as a result of its bactericidal action. 

 Death was not due to Ij^sis. In a full grown, 18-hour- 

 old culture of Streptococcus hemolyticus, 100 ppm. peni- 

 cillin did not decrease the number of viable cells; but 

 with small inocula, after the bacteria w^ere given a chance 

 to multiply, ths same concentration killed almost all the 

 cells at 37°, a smaller number died at 18°, and none at 

 4°. The deathrate constants were 0.100 and 0.027, re- 

 sulting in the very low temperature coefficient Qio = 1-9. 



Remarkable morphological changes are brought about 

 by penicillin, which give a clue in regard to the mode 

 of attack of this drug. Gardner (1940) observed that 

 Clostridium welchii, which is completely inhibited by 17 

 ppm. penicillin, showed, when treated w^ith as little as 1 

 ppm. ''an extreme elongation of the majority of the cells. 



