Determination of MICs of conventional and experimental drugs in liquid medium by the radiometric method against Mycobacterium avium complex

The aim of this study was to search for new drugs active against the Mycobacterium avium complex and to re-examine the activity of some conventional antituberculosis drugs against these species. This progress report describes the protocol and phases of in vitro experiments in a search which included 57 different compounds tested against numerous strains of M. avium clinical isolates. The preliminary screening and MIC determination of these drugs were conducted in 7H12 broth by the radiometric method (BACTEC system). Of the total of 57 drugs, 23 were discarded after preliminary screening and 17 after MIC determination. The remaining 17 drugs were considered sufficiently promising for more detailed in vitro studies. These, now in progress, include MIC determination by two additional methods (in broth by sampling and plating and in 7H11 agar plates), MBC determination and drug combination studies. The following drugs are currently undergoing these detailed studies: isoniazid, rifampin, rifabutine (ansamycin LM427), amikacin, streptomycin, ethambutol, ethionamide, cycloserine, clofazimine (CF), CF derivative B746, CF derivative B1865, ofloxacin, ciprofloxacin, cephalosporin BMY 28142, trimethoprim-sulfamethoxazole, spectinomycin derivative U6633F(B), and dihydromycoplanecin.