242 NATURE OF ANTIBIOTIC ACTION 



rapidly removed from the blood and excreted. It has no effect upon 

 bacteriophage or staphylococci, although o. i milligram per cent inhibits 

 growth as well as blood coagulation by these organisms (675). 



A comparison of the effect of actinomycin with that of tyrothricin 

 and its constituents, tyrocidine and gramicidin, upon the growth of 

 rhizobia (917) showed that, whereas gramicidin inhibited all strains 

 alike, the other three substances inhibited the slow-growing rhizobia 

 much more than the fast-growing ones. Effective and ineffective strains 

 behaved alike. Of the four antibiotic substances, tyrocidine was usually 

 bactericidal, actinomycin was bacteriostatic, and the other two pos- 

 sessed both properties. Some strains of rhizobia were stimulated by lim- 

 ited concentrations of actinomycin. 



Proactinomycin 



Proactinomycin, in low concentrations, lengthens the lag phase of 

 staphylococci, this increase in lag becoming greater in certain media 

 as the size of the inoculum is reduced. One of the primary effects of 

 this antibiotic is believed to be the interference with the synthesis or use 

 of diffusible substances produced by the cells and concerned with the 

 ending of the lag. When the concentration of proactinomycin is in- 

 creased above a certain value, the effect is different: after a period of 

 incipient growth, the cells begin to die. There is thus a qualitative 

 similarity between the effect of proactinomycin and of penicillin (3). 



Clavacin 



Clavacin not only is bacteriostatic on gram-negative bacteria but also 

 possesses marked bactericidal properties, as is brought out in Figure 

 24. Clavacin has an inhibiting effect upon the following respiratory 

 enzyme systems: glucose dehydrogenase, succinoxidase, malic acid 

 dehydrogenase, glycerophosphate dehydrogenase, and tryptophanase 

 (379). Various animal fluids and organs (serum, liver) contain an 

 enzyme which converts clavacin into an acid, due to the hydrolysis of 

 the lactose ringj a marked reduction in its antibiotic action results 

 {S?>S)' Clavacin is also active against fungi, including species of 

 Pythium (24) and C. ulmi (949). 



