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Controlling Microbial Growth



Control of microbial growth is important to many industries and is vital to public health. Sterilization and disinfection, which prevent the spread of microbial growth, are accomplished through external controls with physical and chemical mechanisms. Antibiotics and medicinal antimicrobials are considered internal controls. Sterilization describes the statistically complete (99.9999%) destruction of all microbes, their spores, and endospores. Disinfection refers to the destruction of 99.99% to 99.999% of all pathogenic microbes and other microorganisms, but not necessarily their spores and endospores. Disinfection refers only to a reduction of the number of microbes below a certain threshold. The main physical agents are heating (including dry heat, moist heat, and pasteurization), freezing, desiccation, osmotic pressure changes, radiation, and filtration. The main chemical agents are phenols, halogens, alcohols, heavy metals, and detergents.

At A Glance

  • Sterilization describes the statistically complete (99.9999%) destruction of all microbes, their spores, and endospores, while disinfection is a less extensive process that destroys 99.99% to 99.999% of pathogenic microbes and other microorganisms.
  • Control of microbial growth via heating is accomplished with dry heat, moist heat, or pasteurization.
  • Freezing controls microbial growth, as does desiccation (removal of water). The two processes are often combined as lyophilization, the desiccation of frozen material.
  • Ultraviolet light, ionizing radiation, and microwave ovens are all used to control microbial growth.
  • Surrounding cells with salt or sugar draws water from the cells to the outside environment.
  • Filtration can be used to remove bacteria, and even viruses, from fluids and air.
  • Chemical agents work by damaging cellular structures, including proteins, cell walls and membranes, and nucleic acids.
  • Phenols, halogens, alcohols, heavy metals, and detergents are the main types of chemical agents used in controlling microbial growth.
  • Phenols are aromatic organic compounds that provide long-lasting disinfection by denaturing microbial proteins.
  • Halogens (group 17 elements) are highly electronegative and disrupt the structure of microbes by reacting with essential biomolecules.
  • Alcohols are hydroxyl-containing organic compounds that are accessible and inexpensive disinfectants.
  • Heavy metals (metallic elements with high atomic weights) covalently bond with microbial proteins and denature them.
  • Detergents are common surfactants such as soaps that remove microbes, dirt, and oils.
  • Viruses are controlled by chemical agents called antivirals that damage virus protein coats or genetic material.