Applications and limitations of physical methods of controlling microorganisms

The major physical agents or processes used for the control of microorganisms are temperature (high and low), desiccation, osmotic pressure, radiation, and filtration. Application of few methods and their limitations are as follows:

1. Moist heat:

a. Autoclave:

  • It is used for sterilizing instruments, linens, utensils, and treatment trays, media and other liquids.

Limitations: It is ineffective against organisms in materials impervious to steam. It cannot be used for heat-sensitive articles.

b. Free- flowing steam or boiling water:

  • It is used for the destruction of non- spore forming pathogens and is also used for sanitizing bedding, clothing and dishes.

Limitations: It cannot be guaranteed to produce sterilization on one exposure.

2. Dry heat:

a. Hot air oven:

  • It is used for sterilizing materials impermeable to or damaged by moisture, e.g. oils, glass, sharp instruments and metals.

Limitations: It is destructive to materials which cannot withstand high temperatures for long periods.

b. Incineration:

  • It is the method of burning the materials and is used for the disposal of contaminated objects that cannot be reused.

Limitations: A large incinerator is required to burn large load promptly and completely and with potential risk of air pollution.

3. Radiation:

a. UV light:

  • It is used in the control of airborne infection and the disinfection of surfaces.

Limitations: UV rays must be absorbed to be effective but it doesn’t pass through transparent glass or opaque objects as it has low penetration. It is also irritating to eyes and skin.

b. X-rays, gamma and cathode radiation:

  • They are used for the sterilization of heat-sensitive surgical materials and other medical devices.

Limitations: They are expensive and require special facilities for use.

4. Filtration:

a. Membrane filters: They are used for the sterilization of heat-sensitive biological fluids.

Limitations: Only those fluids which are relatively free of suspended particulate matter can be sterilized.

b. Fiberglass filters or High efficiency particulate air (HEPA) filters:

  • It is used for the disinfection of air.

Limitations: It is expensive.

5. Physical cleaning:

a. Ultrasonics:

  • It is effective in decontaminating delicate cleaning instruments.

Limitations: It is not effective alone but when used as adjunct procedure enhances the effectiveness of other methods.

b. Washing:

  • It is used to clean hands, skin, objects etc.

Limitations: It is only used as a sanitizing process and reduces microbial flora.

Applications and limitations of physical methods of controlling microorganisms