Factors That Encourage and Limit the Growth of Microorganisms

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Factors That Encourage and Limit the Growth of Microorganisms


        In the laboratory, bacteria are normally grown (cultured) in either liquid medium in flasks, bottles or fermenters, or solid medium in Petri dishes.  Introduction of microbes into or on to these media is called inoculation.  The nature of the medium depends on the microorganism’s natural environment and on the reason why it is being grown.  Normally, to isolate large numbers of microbes, liquid culture is used but solid medium is used for the isolation of individual bacteria and for storage.  

        As bacteria are a very differing group of microbes that can exist in a wide range of environments, the ingredients in the medium will depends on the individual species.  


        Most bacteria have characteristic temperature ranges of growth with a maximum, minimum and optimum growth temperature.  Certain bacteria have become adapted to living at temperatures as low as -10OC, while having an optimum growth temperature of around 20OC.

Oxygen Concentration

Bacteria vary in their requirements for oxygen, depending on the nature of their metabolism.  Aerobes are bacteria that are capable of growing in the presence of oxygen; anaerobes are bacteria that do no require oxygen for growth.  Within this, are obligate anaerobes that die in the presence of O2; facultative anaerobes such as E. coli which grow much better in the presence of O2 but can grow anaerobically; aerotolerant anaerobes that ignore the presence of O2 and grow equally well with or without; and microaerophilic bacteria that are damaged by normal atmospheric conditions, and only survive in areas of very low concentrations of O2.

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        Bacteria can grow at high pH (8.5-11.5) are called alkaliphiles.  Acidophiles are those that grow at low pH (0.5-5).  However, most microbes need near neutral conditions for optimum growth.  Keeping pH constant can be difficult, so to check it, a pH meter or pH probe may be used to regulate it.  

Water Activity

        Like all organisms, microbes are sensitive to the osmolarity of the surrounding medium; at low osmolarity, water will be accumulated in the cell and at high osmolarity water will be lost.  Lysis of the cell at low osmolarity is prevented by ...

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