ANTIBIOTICS 153 



KNAPWEED 



It is of interest to note the variety of sources from which antibiotics are being 

 obtained. The synthetic activities of moulds and mould-like bacteria are so diverse 

 that they have constituted a prolific source of new compounds, but plants are also 

 contributing to the store. Cavalhto and Bailey (1949) have obtained from the leaves 

 of the spotted knapweed an unsaturated lactone with antibacterial activity which is 

 rapidly destroyed by cysteine and thioglycollic acid. It is concluded that lipophilic 

 antibiotics are more active against Gram-positive organisms. 



POLYMYXIN 



This group of polj^eptides investigated by Stansly, Shepherd and White (1947), 

 and Ainsworth, Brown and Brownlee (1947) contains the amino acids 1-threonine, 

 1-ay-diaminobutyric acid, d-leucine, phenylalanine, d-serine and an unidentified 

 fatty acid. Chromatographic absorption has facilitated characterisation of this group. 



STREPTOTHRICIN 



Streptothricin is a basic substance obtained from Streptomyces lavendulce 

 (Waksman, 1943). 



AUREOMYCIN 



Described by Duggar (1948) this antibiotic with the trade name, Duomycin, is 

 obtained from Streptomyces aureofaciens. Its chief advantages are that resistant 

 strains are not readily developed and it has proved of value in urinary infections and 

 some virus diseases (psittacosis-lymphogranuloma group and rickettsiae). 



NEOMYCIN 



Waksman and LechevaUer (1949) obtained neomycin from a soil organism 

 Actinomyces (or Strejptomyces) fradii {ov fradice). It inhibits the growth of strepto- 

 mycin-resistant tubercle bacilli and salmonellse, and hence its potential value. It 

 is basic in nature and thermostable, and organisms appear not to develop neomycin- 

 resistance readily. 



Summary of Chapter VII 



The mode of action of chemotherapeutic agents and antibiotics, their relation to 

 metaboHc processes and enzyme systems, and problems of bacterial resistance and 

 drug fastness, are discussed. 



