Extracellular hemolytic activity in rapidly growing mycobacteria

Little is known about virulence factors associated with rapidly growing mycobacteria. We evaluated 42 clinical isolates of Mycobacterium fortuitum and Mycobacterium chelonae and 4 reference strains of Mycobacterium smegmatis for the production of hemolysin (or hemolytic substance) as a possible contributor to the pathogenesis of disease caused by these organisms. All the strains tested possessed extracellular hemolytic activity that was stable after heating and proteinase treatment, and the active substance had a molecular weight less than 10,000. The activity accumulated in culture medium during the late exponential to mid stationary phase of growth. Hemolysis in vitro was relatively slow; incubation for 10 h at 35 degrees C was required to obtain maximal activity. Some specificity of the hemolysis with regard to red blood cells from different animals was observed.