Interrelationship among colonial morphology, susceptibility to antituberculosis drugs, growth rate, and viability in Dubos liquid medium in Mycobacterium avium complex strains

Abstract

Interrelationship among colonial morphology, susceptibility to antituberculosis drugs, growth rate, and viability in Dubos liquid medium were studied in Mycobacterium avium complex strains, which were not exposed to any antituberculosis drugs. All five strains that were relatively susceptible to the majority of antituberculosis drugs formed smooth, opaque, domed colonies (SmD) on 7H10 agar medium, and all five strains that were naturally resistant to those drugs formed smooth, transparent, flat colonies (SmT). The SmD colony-forming strains showed small, domed, smooth colonies (DS-type) on Ogawa egg medium, and the SmT colony-forming strains usually large, flat, wrinkled colonies (FW-type) on Ogawa egg medium. However, there was one exceptional strain (11004) that formed DS-type colonies on Ogawa egg medium and SmT-type on 7H10 agar medium. Accordingly, the SmD morphology correlated with drug susceptibility and the SmT colonial morphology with drug resistance. All six DS-colony-forming strains had slow growth rates on Ogawa egg medium, whereas all four FW-colony-forming strains had rapid growth rates on Ogawa egg medium. However, such correlation was not observed in Dubos liquid medium. When the viability was defined as a ratio of the number of colony-forming units contained in 1 mg wet weight of bacteria, the five drug-susceptible strains usually showed low viability and the five drug-resistant strains showed high viability in the Dubos liquid medium. The above four characteristics, colonial morphology, drug susceptibility, growth rate on Ogawa egg medium, and viability in Dubos liquid medium, usually correlated with each other.(ABSTRACT TRUNCATED AT 250 WORDS)