tokens: The bactericidal activity of six new rifamycin derivatives - - rifabutin ( RBU ) , FCE 22250 ( F22 ) , rifapentine ( RPE ) , CGP 29861 ( C29 ) , CGP 7040 ( C70 ) and CGP 27557 ( C27 ) and rifampicin ( RMP ) - - have been measured against log phase and , as a better test of sterilising activity , against stationary phase cultures of Mycobacterium tuberculosis , H37Rv .