Laboratory Outline for General Bacteriology 



THERMAL DEATH POINT 



The thermal death point of an organism is customarily defined 

 as the least temperature that will destroy it in ten minutes under 

 known conditions. Several factors influence the thermal death 

 point. Old cultures are less resistant than younger ones. An acid 

 medium renders heat much more effective. Moist heat is much 

 more efficient than dry heat. For comparative work it is necessary 

 to use media of uniform reaction and composition. The presence 

 of spores indicates that the organism has two thermal death points ; 

 one for the spores and another lower one for the vegetative cells. 

 The medium recommended by the Committee on Identification of 

 Species of the Society of American Bacteriologists, is nutrient 

 broth. Several tubes are inoculated then heated in water baths 

 at different temperatures ranging usually from 50 C to 70 C for 

 10 minutes. They are then incubated to see if growth takes place. 



Fermentation Tube Chart 



PLATE 2. 



