268 DISEASE CONTROL 



influenza virus (789). The purest preparation of penicillin so far avail- 

 able completely inhibited (275) the growth of S. aureus in a dilution 

 of between i : 24,000,000 and i : 30,000,000. Partial inhibition was ob- 

 tained up to 1:1 60,000,000. Salmonella organisms were also sensitive. 

 Certain strains of Brucella are sensitive to penicillin in vilro, this effect 

 being enhanced by the presence of small amounts of sodium sulfathia- 

 zole (918). The sensitivity of most strains of S. hemolytkus is similar 

 to that of the majority of staphylococci and meningococci j pneumo- 

 coccus and alpha streptococcus strains fall, in sensitivity, between the 

 beta streptococci and the meningococci (628). Similar variations in 

 sensitivity to penicillin of different strains of the same organism have 

 been observed for various other bacteria, such as C. difhtheriae. 



A partial list of the organisms susceptible to penicillin is given in 

 Table 42. 



The antibacterial activity of penicillin is not interfered with by sub- 

 stances that inhibit sulfonamides, namely, bacterial extracts, pus fluids, 

 tissue autolysates, peptones, and ^-amino-benzoic acid. It is nontoxic in 

 concentrations far greater than those required for therapeutic purposes. 

 It is rapidly excreted through the kidneys and frequent administration 

 is essential in order to maintain a proper blood concentration. 



In its biological properties, penicillin has been found, in general, to 

 resemble sulfonamide drugs, with certain significant differences (5): 



The bacteriostatic power of penicillin against streptococci and staphylo- 

 cocci is greater than that of sulfonamides, even when the tests are 

 made under conditions optimum for the action of the latter. Satu- 

 rated solutions of sulfapyridine and sulfathiazole showed no com- 

 plete inhibition of bacteria on the assay plate, whereas peniciUin, even 

 in a dilution of 1 1500,000, gave considerable inhibition. 



The action of penicillin on streptococci and staphylococci, unlike that of 

 the sulfonamides, is influenced very little by the number of bacteria 

 to be inhibited. Bacterial multiplication can be completely prevented 

 by as low a concentration of penicillin as 1 : 1,000,000, even if the 

 inoculum contains several million bacterial cells. In the case of 

 smaller inocula, inhibition occurs in even higher dilutions. This prop- 

 erty of penicillin is believed to be of great importance in the treat- 

 ment of heavily infected wounds, on which the sulfonamide drugs 

 seem to have little beneficial action. 



