organisms can be killed by being exposed to a temperature of 80 °C (176 °F) for 

 10 minutes. In the case of spores, anthrax spores will be killed by exposure to a 

 temperature of 100 °C (212 °F) for 10 minutes, but Clostridium hotulinum and C. 

 suhtilis spores can withstand boiling for hours. 



3. Pasteurization: This is one specialized application of moist heat. It is important 

 to note that pasteurization does not kill all of the micro-organisms in milk or 

 other liquids. It is intended to reduce bacterial contamination and, in the case 

 of milk, to kill Mycobacterium bovis, Brucella abortus, and Salmonella without 

 altering the flavor or nutritional quality of the milk any more than necessary. 

 The phosphatase test is used to check for adequate milk pasteurization because 

 phosphatase is destroyed by heat sufficient to kill the listed pathogens. 



4. Autoclaving: The use of autoclaving for disinfection is based on the fact that 

 water boils at higher temperatures when pressure is raised. Water boils at 100 °C 

 (212 °F) at sea level, whereas when atmospheric pressure reaches 15 lb/in-, it boUs 

 at 121 °C (250 °F). The higher temperature and moist heat significantly reduce the 

 time necessary to penetrate any porous materials in the autoclave. 



5. Dry heat (e.g., flame, baking): Dry heat is less effective than moist heat. 

 Vegetative micro-organisms are more resistant to dry heat than they are to moist 

 heat, and spores are even more resistant. Some examples of the application of 

 dry heat include the incineration of carcasses, the heating of a bacterial loop in a 

 Bunsen burner flame, the searing of a surface before sample collection, and the 

 cauterization of a wound. 



6. Radiation: Radiation is classified as nonionizing or ionizing according to its 

 energy level. 



• Nonionizing radiation includes a spectrum of electromagnetic waves on 

 a continuum from radio waves to infrared, visible, and finally ultraviolet 

 (UV) light. 



• Ionizing radiation is radiation in which each particle or photon has 

 high enough energy to cause ionization within material it encounters. 

 Ionization is the stripping off of electrons from an atom in the material 

 encountered. Each atom with the electron stripped off becomes a positive 

 ion; the electron becomes a negative ion. The biologically lethal effects are 

 caused by DNA strand breakage. 



7. Filtration: Filters and ultrafilters can be used to remove micro-organisms from 

 gases and fluids. Filtering is used to produce micro-organism-free solutions when 

 other methods would be detrimental to the product (e.g., in the production of 

 fetal calf serum). Fiigh-efficiency particulate air filters are used to filter air for 

 surgical suites, laboratories, and industrial processes and to ensure the safety of 

 air discharged from biological safety cabinets. 



7-7 



