Although ultraviolet light has been used to sterilize air, water, and a variety of other
materials, it has a disadvantage in these applications in that solid particles, even though
microscopic in size, may shield microorganisms from the radiation. Ultraviolet lights are
used in many meat-hanging rooms to reduce bacterial and mold contamination.
b. Other Radiation Sources. Ionizing atomic radiations such as alpha particles
and x-rays are also harmful to microorganisms. In general, these types of radiation
require more energy to kill bacteria than does ultraviolet light.
1-26. INHIBITION OR DESTRUCTION
Microorganisms are inhibited and destroyed by a wide variety of chemical agents
and physical processes. Some of the terms used in relation to inhibiting or destroying
microorganisms are: antiseptic, disinfectant, germicide, and sterilization. An antiseptic
is an agent that inhibits the growth of microorganisms. A disinfectant or germicide is an
agent that kills microorganisms. Sterilization is the process of freeing a substance of all
living microorganisms.
a. Factors. There are a number of factors that have a direct influence on
antiseptics, disinfectants, and sterilization. Concentration of the chemical agent is
important. A high concentration will sterilize or disinfect in a shorter period of time. A
50 percent reduction in the concentration of a disinfectant will decrease its efficiency by
a ratio of 1 to 4. Time of exposure to the agent is important. In no case is death to all
organisms instantaneous, so the agent must be given enough time to complete its
action. The number of organisms present is important. As a rule, it is more difficult to
inhibit or kill large numbers of microorganisms than small numbers. This is particularly
true if there is a wide variety of organisms present in large numbers. The kind of
microorganisms present will determine the efficiency with which they are inhibited or
destroyed. Spores are more resistant than vegetative cells. Encapsulated varieties of a
species are more difficult to kill or inhabit than nonencapsulated varieties. The medium
surrounding the microorganisms is an important consideration. Heat in the presence of
moisture and dry chemicals in solution will kill more rapidly. Some substances in
solution tend to protect microorganism, while other increase their susceptibility to
antiseptics or disinfectants. Generally, microorganisms will be more resistant when the
pH is one that is satisfactory for their growth. The efficiency of disinfectants increases
as the temperature is raised.
b. Physical Processes. There are several physical processes that will inhibit or
destroy bacteria. Desiccation is an important physical process. Dried substances often
contain large numbers of microorganisms, but they do not deteriorate because the
microorganisms cannot grow without moisture. An increase in osmotic pressure will
adversely affect many microorganisms. The use of salt and sugar aid in preserving food
products by exerting an elevated osmotic pressure on the microorganisms that is
present. Low temperatures inhibit microorganisms by the physical effects of the
temperature and by
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