ANTIBACTERIAL ACTION 237 



Inhibition by 0.002 O.U./ml. More than 40 per cent of the strains thus 

 Isolated could be called resistant j this was especially true of the strains 

 isolated from patients who received penicillin. 



The oxygen uptake of suspensions of staphylococci was not inhibited 

 to any extent by the action of penicillin for 3 hours. In a concentration 

 of I : ijOOOj after incubation for 24 hours at 37° C, the bacteria gave 

 larger numbers of colonies on plating (5). Although 0.0 1 to o.i mg. of 

 penicillin per milliliter was found (432-437) to be sufficient to inhibit 

 the growth of 2,500,000 hemolytic streptococci (Group A), no con- 

 clusion could be reached as to whether its action is truly bactericidal or 

 merely bacteriostatic. 



Penicillin inhibits fibrinolysis by sensitive strains of S. -pyogenes; this 

 phenomenon is believed to be connected with growth inhibition (183). 



A comparison was made of the amounts of crude penicillin and 

 gramicidin required to bring about total inhibition of growth of bac- 

 teria, on the basis of micrograms per milliliter of culture medium 

 (rabbit's plasma and a serum extract of chick embryo) . The results were 

 as follows: 



The two substances appeared to be as effective against bacteria in cul- 

 tures containing growth tissue as in cultures in which no tissue was 

 present (394,395). 



Inhibition of growth of 2 to 4 million hemolytic streptococci was ob- 

 tained by the use of 0.03 \\g penicillin with an activity of 240 to 250 

 O.U./mg. (432, 437). No inhibition was obtained with peptone, 

 /)-amino-benzoic acid, blood, or serum. The fact that both penicillin and 

 sulfonamides act upon some bacteria and are ineffective upon others 

 suggests a similarity In their mode of action (648). A marked differ- 

 ence was found, however, in the action of penicillin and sulfonamides, 



