Physical Methods of Filtration

Controlling Microbial Growth in the Environment

• Most environments, including cars, are not sterile, and can harbor a significant number of microbial colony-forming units (CFUs).
• The concept of "clean" is relative, and the level of cleanliness required depends on the intended use of an item.
• Sterilization is not always practical or necessary, as it can be time-consuming, labor-intensive, and may have toxic effects on users or degrade the quality of the item being treated.

Terminology of Microbial Control

• Fomites are inanimate items that can harbor microbes and aid in disease transmission.
• Two factors determine the level of cleanliness needed: the application of the item and the level of resistance to antimicrobial treatment by potential pathogens.
• Aseptic technique is necessary to prevent contamination of sterile surfaces and to prevent the introduction of microbes into a patient's body.
• Sterile fields must be free of all vegetative microbes, endospores, and viruses.

Selecting an Antimicrobial Agent

• Antimicrobial agents can be classified into two categories: -cides (kill targeted microorganisms) and -static (inhibit the growth of microorganisms).
• The choice of antimicrobial agent depends on the type of microorganism, the level of resistance, and the intended use of the item.
• Susceptibility of microorganisms to antimicrobial agents varies, and the effectiveness of an agent can be measured by the decimal reduction time (DRT).

Measuring Microbial Control

• The effectiveness of a disinfecting agent or microbial control protocol depends on several factors, including:
  • The length of time of exposure
  • The concentration of the disinfecting agent
  • The susceptibility of the microorganism to the agent
  • Environmental conditions, such as pH and temperature
  • The presence of bodily fluids, tissue, or biofilms on surfaces

Action of Antimicrobial Agents

• Antimicrobial agents can alter the cell wall, membrane, proteins, or nucleic acids of microorganisms.
• Different agents have different modes of action, and the choice of agent depends on the type of microorganism and the intended use of the item.

Physical Methods of Microbial Control

• Heat-related methods, including:
  • Moist heat: kills microorganisms by denaturing proteins, disrupting cell membranes and cell walls, and disrupting the structure of nucleic acids.
  • Dry heat: used for products that cannot get wet, such as powders, oils, and some metals.
  • Autoclaving: uses pressure to achieve boiling temperatures above 100°C, killing all microorganisms.
  • Pasteurization: used for food products, such as milk, ice cream, and fruit juices, to kill harmful bacteria.
• Other physical methods, including:
  • Refrigeration and freezing: slows down microbial growth and metabolism.
  • Desiccation and lyophilization: removes water, inhibiting microbial growth.
  • Filtration: uses a sieve to remove microorganisms from a liquid or gas.
  • Osmotic pressure: uses salt or sugar to remove water, inhibiting microbial growth.
  • Radiation: uses ionizing or non-ionizing radiation to kill microorganisms.

Chemical Methods of Microbial Control

• Chemical agents can be used to control microbial growth, including:
  • Phenol and phenolics: denature proteins and disrupt cell membranes.
  • Alcohols: denature proteins and disrupt cell membranes.
  • Halogens: denature proteins and disrupt cell membranes.
  • Oxidizing agents: denature proteins through oxidation.
  • Surfactants: decrease the surface tension of water, disrupting cell membranes.
  • Heavy metals: denature proteins.
  • Aldehydes: denature proteins.
  • Gaseous agents: denature proteins.
  • Enzymes: denature proteins.
  • Antimicrobials: have a wide range of actions, including denaturing proteins, disrupting cell membranes, and inhibiting microbial growth.

Selecting an Antimicrobial Agent

• Ideally, antimicrobial agents should be:
  • Readily available
  • Inexpensive
  • Fast-acting and easy to use
  • Stable during storage
  • Non-toxic, non-allergenic, and non-corrosive
  • Capable of controlling microbial growth while being harmless to humans, animals, and objects.