IN VITRO AND IN VIVO STUDIES OF GRAMICIDIN, TYROTHRICIN AND TYROCIDINE

¹ From the Merck Institute for Therapeutic Research, Rahway, N. J.

1. Tyrocidine and tyrothricin appear to exert a marked bactericidal action on aerobic and anaerobic gram-positive bacteria in the absence of blood or serum. Under similar conditions gramicidin appears to be primarily bacteriostatic.

2. In the presence of blood or serum tyrocidine and tyrothricin lose their bactericidal properties whereas gramicidin retains its bacteriostatic properties. Under these conditions tyrothricin becomes primarily bacteriostatic, apparently by virtue of its gramicidin content.

3. In vivo results indicate that when mice are infected and treated by intraperitoneal injection, gramicidin and tyrothricin are active whereas tyrocidine is not. Gramicidin or tyrothricin are only effective when given in direct contact with the infecting bacteria.

4. No protection was afforded to mice infected by intraperitoneal injection when treatment was given by oral, subcutaneous or intravenous administration. Likewise, mice infected by vein were not protected by intraperitoneal treatment.