Microbial Resistance & Control: Key Concepts

Microbial Resistance Levels

Understanding the varying levels of microbial resistance is crucial for effective control strategies.

Categories of Microbial Resistance

• Highest Resistance: Prions and bacterial endospores.
• Moderate Resistance: Protozoan cysts, some fungal spores, and some non-enveloped viruses.
• Least Resistance: Bacterial vegetative cells, other fungal spores and hyphae, enveloped viruses, yeast, and trophozoites.

Terminology of Microbial Control

Precise terminology is essential when discussing methods for controlling microbial growth and survival.

Sterilization

The process of destroying all forms of microbial life, including endospores, on an object or in a material.

Absolute Sterilization

Sterilization is an absolute process; there are no degrees of sterilization.

Main Methods of Sterilization

1. Moist Heat: Typically 121°C for 15 minutes at 15 PSI.
2. Dry Heat: Commonly 170°C for 120 minutes.
3. Ionizing Radiation: Effective for heat-sensitive materials.
4. Gases: Such as ethylene oxide, used for sterilizing medical devices.

Disinfection

The process of destroying vegetative pathogens but not necessarily endospores or viruses.

Disinfectant

A chemical agent applied to an object or a material to:

• Reduce or inhibit microbial growth.
• Usually a liquid applied to a surface.
• Can be a solution added to eliminate pathogens in water (e.g., chlorination).

Antisepsis

Chemical disinfection applied to the skin, mucous membranes, or other living tissues.

• Often used for the treatment of wounds.
• A specific kind of disinfection tailored for living tissue.

Germicide

A chemical agent that rapidly kills microbes but not necessarily endospores.

• Bactericide: Kills bacteria.
• Sporicide: Kills endospores.
• Fungicide: Kills fungi.
• Virucide: Kills viruses.
• Amoebicide: Kills amoebas.

Suppression of Organisms

Methods that inhibit microbial growth without necessarily killing the organisms.

Bacteriostasis

A condition in which bacterial growth and cell division are inhibited.

• Bacteria are not killed.
• Removal of the bacteriostatic agent results in renewed bacterial growth and cell division.

Examples of Bacteriostasis

• Refrigeration: Typically 4°C.
• Chemicals: Many chemicals, such as certain dyes, exhibit bacteriostatic properties.

Fungistasis

The inhibition of fungal growth.

Asepsis

The absence of pathogens from an object or area.

• Aseptic Techniques: Designed to prevent the entry of pathogens into the body.
• Surgical Asepsis: Designed to exclude all microbes from a surgical field.
• Medical Asepsis: Designed to exclude microbes associated with communicable diseases.

Techniques in Asepsis

1. Air filtration.
2. Ultraviolet light.
3. Personnel masks, gloves, and gowns.
4. Instrument sterilization.

Degerming

The removal of transient microbes from the skin by mechanical cleansing or by the use of an antiseptic.

• Alcohol swabs on skin before injection.
• Iodine-containing products used before surgery.

Sanitization

The reduction of pathogens to safe public health levels on eating utensils by mechanical cleansing or chemicals.