Investigation of the effect of heat enhancement on the growth of mycobacteria in radiometric medium.

The enhancement of the growth rate of 11 clinical isolates of mycobacteria, covering six species, were investigated in vials of Middlebrook 7H12 medium which had previously been heated to 60 degrees C, 70 degrees C or 80 degrees C. The optimal temperature which enhanced growth was 70 degrees C. The enhancing effect remained stable for over 3 months. Trypsin treatment of the medium abolished the enhancing effect of heat, but this could be restored by the addition of heated or unheated bovine serum albumin. Protein electrophoresis demonstrated altered electrophoretic mobility of heated bovine serum albumin. It is suggested that this altered bovine serum albumin is the component which promotes enhanced mycobacterial growth.