CHANGE IN COLONY MORPHOLOGY INFLUENCES THE VIRULENCE AS WELL AS THE BIOCHEMICAL-PROPERTIES OF THE MYCOBACTERIUM-AVIUM COMPLEX

Factors that influence colony morphology are of crucial importance for drug development as well as for understanding the virulence of Mycoba cterium avium complex (MAC) strains. The MAC 101 strain used in the pr esent study grows as smooth transparent (SmT) colonies that tend to be come opaque and pigmented when incubated for long periods of time. How ever, when MAC was passaged in animals, two types of colonies were rec overed. The new rough transparent (RgT) colony morphology appeared mor e flat and transparent, having a central spot, irregular edges at time s, and a dry, granular appearance like that of the rough mutants. In a nimal studies, the RgT bacilli multiplied at a much faster rate than t hat of the SmT bacilli, causing 60-80% mortality compared with the 10% mortality observed in mice infected with SmT. in vitro studies indica ted that the SmT MAC did not grow and multiply as well in reside;nt pe ritoneal macrophages as the RgT MAC did. The two morphotypes did not d iffer in their growth rates in vitro but the RgT MAC failed to reduce dimethylthiazol-diphenyltetrazolium bromide (MTT), alamar blue and neu tral red, suggesting that there might be significant changes in the ce ll wall or elsewhere causing changes in cellular permeability. These t wo morphotypes could serve as models for studying the biochemical mark ers or the identification of factors responsible for the virulence of the MAC. (C) 1998 Academic Press.