SUBSTANCES PRODUCED BY BACTERIA 161 



Quinones and ketones, namely, fumi'gatin, citrinin, spinulosin, clavacin, 



and penfcillic acid 

 Organic bases, including streptothricin, streptomycin, and proactinomycin 



On the basis of their biological activity, the antibiotic substances also 

 vary considerably. They may be divided into three groups: 



Primarily bacteriostatic agents, such as penicillin, actinomycin, and pro- 

 actinomycin 



Substances which are bactericidal but not bacteriolytic, including pyocya- 

 nase, gliotoxin, fumigacin, clavacin, and pyocyanin 



Bacteriolytic substances, namely, gramicidin, actinomycetin, and lysozyme 



On the basis of their toxicity to animals, antibiotic substances may 

 also be divided into three groups: 



Compounds that are nontoxic or but slightly toxic; here belong penicillin, 

 streptomycin, flavicin, pyocyanase, and actinomycetin 



Compounds of limited toxicity, including gramicidin, tyrocidine, citrinin, 

 streptothricin, and fumigacin 



Highly toxic compounds, such as actinomycin, gliotoxin, aspergillic acid, 

 and clavacin 



Many of the antibiotic substances are thermostable, others are ther- 

 molabile ; some pass readily through Seitz and other filters, others are 

 adsorbed. The various methods of isolation of these substances are based 

 upon their chemical nature, solubility, and properties of adsorption. 



SUBSTANCES PRODUCED BY BACTERIA 



Lipoids and Pigments. Ps. aeruginosa, discovered by Gessard in 

 1882 (320) and formerly known under the names of Bacterium fyo- 

 cyaneuni and Bacillus fyocyaneus, was the first organism found to pro- 

 duce two antibiotic agents, the colorless pyocyanase and the pigment 

 pyocyanin. Pyocyanase, believed to be of the nature of an enzyme, is 

 now recognized as a lipoid containing unsaturated fatty acids {SS^ 4^9? 

 410). Recently this organism was shown to form (809) three com- 

 pounds that possess antibacterial properties, namely, pyocyanin, 



