PATHOBIOLOGICAL SIGNIFICANCE OF COLONY MORPHOLOGY IN MYCOBACTERIUM-AVIUM COMPLEX

Mycobacterium avium complex (MAC) strains are known to exhibit variati on in colony morphology. In addition to the smooth transparent (ST), s mooth opaque (SO) and rough opaque (RO), which are the most common mor phological forms, intermediate (IM) and pin point (PP) forms were also occasionally observed. In order to understand the pathobiological sig nificance of these different colony forms, we investigated their virul ence in beige mice, ability to bind to plastic and epithelial cells, d ifferences in the lipids, and modulation of macrophage functions by th e bacillary extracts. ST variants, the most common form seen in AIDS p atients, were more virulent with increased multiplication in lungs, li vers and spleens of beige mice and showed increased adherence to plast ic and epithelial cells. SO, RO, PP colonial forms did not show increa se in growth in any of the organs over a period of 4 weeks. IM colonia l variants showed increased growth in lungs and spleens but not in liv ers. Thin layer chromatographic (TLC) analysis of lipid extracts showe d one specific component in the high polar lipids of the SO variant, w hile ST variant did not show any specific component in any of the thre e families of lipids (high, intermediate and low polarity). The RO var iant either expressed low levels or lost many of the components of lip ids of high and intermediate polarity, however produced increased leve ls of lipids of low polarity. One of the components of low polar lipid s was specific for RO variant and was produced in large quantity. The isogenic variants differed in the total lipid and sugar contents and a lso differed in their ability to modulate macrophage functions. (C) 19 96 Academic Press Limited