Antibiotic Groups 



With the increasing number of antibiotics isolated from cultures of 

 actinomycetes, whether in a crystalline state or as active crude preparations, 

 certain broad groups become recognized. These groupings are based on 

 biological properties, solubility and other physical properties, chemical 

 properties, or utilization as chemotherapeutic agents. Advantage has been 

 taken of these characteristics in the preparation of detailed keys for identi- 

 fication. For purposes of simplification, however, the antibiotics can be 

 divided into twelve presently indicated groups. There is, of course, con- 

 siderable overlapping among these groups, and often a particular substance 

 may be placed with as much justification in one group as in another. There 

 are also a number of preparations known that do not fit readily into any 

 of these major groups but may be said to be closely related. 



1. The actinomycin group. This group comprises substances which are 

 soluble in organic solvents and to only a limited extent in water. They are 

 active largely against gram-positive bacteria and to a much lesser extent 

 against gram-negative bacteria and fungi. Many of them are pigmented, 

 ranging from red and orange to yellow. Most of them are highly toxic to 

 animals. 



2. The acid-base indicator group. These substances change their color 

 depending on reaction of substrate. They are mostly active against gram- 

 positive bacteria. 



3. The streptothricin group. Members of this group are active against 

 bacteria, including certain gram-positive and gram-negative forms, and 

 fungi. They are basic substances, readily soluble in water and insoluble in 

 most organic solvents. They contain amino acids. They are nonpigmented 

 and possess a certain delayed toxicity to animals. 



4. The streptomycin group. Members of this group are active against 

 bacteria and actinomycetes but not against fungi and viruses. They are 

 basic substances, soluble in water and insoluble in most organic solvents. 

 They give maltol or isomaltol on hydrolysis. They are nonpigmented. They 

 are not readily absorbed from the digestive system and possess very limited 

 toxicity to animals. 



5. The neomycin group. Active against gram-positive and gram-negative 

 bacteria but not upon fungi or viruses. They are basic substances soluble 

 in water and not in organic solvents. They are not readily absorbed from 

 the digestive system. They have a toxic auditory effect when given parenter- 

 ally, but are relatively nontoxic orally. They can be differentiated from the 



168 



