42 



NATURE, FORMATION, AND AC'TIVITIlvS 



Table 1(3 



Dirholoiiiir kei/J'nr iileiitijicalion of Slreptonu/rcfi antibiotics (Teilloii, 10.53) 

 + = jiositivp inhibition; = no inhil)ition. 







Streptomycin 



St rp|)toniycin culture 

 Oxytetracj-cliue culture 



( )xvtetracvline 



+ 



Oxytetracyline culture Streptomvcin culture 

 Biotype .S. rimosKS Biotype »S. griseiis 



+ 



Chloramphenicol culture 

 Chlortetracycline culture 

 Streptothricin culture 

 Neomycin culture 

 Antibiotic X culture 



-Chlortetracycline h 



- Chloramphenicol 



Chlortetracycline 

 culture 



i 

 Biotype S. aureo- 

 faciens 



+ 



Chloramphenicol 



culture 

 Streptothricin 



culture 

 Neomycin culture 

 Antibiotic X 



culture 



Chloramphenicol 

 culture 



i 

 Biotype S. venezuelae 



-Streptothricin 1 + 



Streptothricin culture Antibiotic X culture 



i 

 Biotype S. lavendulae 



gram-negative, anaerobic baoteria, myco- 

 bacteria, actinomycetes, and fungi, l)oth 

 filamentous and yeast forms. In such deter- 

 mination of activity, dilution methods are 

 preferable to diffusion methods, since some 

 antibiotics which are very active on a weight 

 basis do not diffuse readily in agar media. If 

 possible, such an antibacterial-antifungal 

 spectrum should l)e complemented with 

 studies of antiprotozoal, antialgal, antirick- 

 ettsial, antiviral, and antitumor activity. 



Two different antibiotics may have very 

 similar antimicrobial spectra. This is true 

 of the antifungal polyenes candidin and 



Streptothricin cultvire 

 Neomycin culture 

 Antibiotic X culture 







Neomvcin- 



Neomvcin culture 



i 

 Biotype <S. fradiae 



+ 



Streptothricin culture 

 Antibiotic X culture 



amphotericin B, which have been differ- 

 entiated biologically only with great care 

 (Lechevalier, 1900). 



Mutants of microorganisms resistant to 

 known antibiotics are usually included 

 among the test organisms used for the deter- 

 mination of antimicrobial spectra. If there 

 is no cross-resistance between two otherwise 

 closely related antibiotics it can be assumed 

 that the antibiotics are different. However, 

 there usually is cross-resistance between 

 closely related compounds and this may even 

 occur between very different substances, as 

 was demonstrated by Pledger and Lecheva- 



