Physical Methods of Microbial Control

Fomite

Inanimate object that can harbor microbes

Biological Safety Level (BSL)

Level of cleanliness and control required in working with organisms

Sepsis

Refers to microbial contamination. In medical setting, refers to toxic inflammation associated with septic shock

Asepsis

The absence of significant contamination

Disinfection

Reduces or destroys microbial load of an inanimate item through application of heat or antimicrobial chemicals

Sanitization

Reduces microbial load of an inanimate item to safe public health levels through application of heat or antimicrobial chemicals

Sterilization

Completely eliminates all vegetative cells, endospores, and viruses from an inanimate item

Fomite

Disinfection (Used on Fomite of Living Tissue)

Fomite

Sanitization (Used on Fomite or Living Tissue)

Fomite

Sterilization (Used on Fomite of Living Tissue)

Antisepsis

Reduces microbial load on skin or tissue through application of an antimicrobial chemical

Degerming

Reduces microbial load on skin or tissue through gentle to firm scrubbing and the use of mild chemicals

Living Tissue

Antisepsis (Used on Fomite of Living Tissue)

Living Tissue

Degerming (Used on Fomite of Living Tissue)

To kill

Suffix -cidal meaning

Prevents growth

Suffix -static meaning

Boiling, Autoclave, Pasteurization

Three types of heat treatments that denatures proteins and alters membranes

Dry-heat oven

Heat treatment that denatures proteins and alters membrane, dehydration, desiccation

Incineration

Heat treatment that destroys by burning

Thermal Death Point (TDP)

Lowest temperature at which all cells in a culture are killed in 10 min

Thermal Death Time (TDT)

Time during which all cells in a culture are killed

Refrigeration

Inhibits metabolism (slows or arrests cell division)

Freezing

Stops metabolism, may kill microbes

High Pressure processing

Denatures proteins and can cause cell lysis

Hyberbaric oxygen therapy

Inhibits metabolism and growth of anaerobic microbes

High pressure processing and hyberbaric oxygen therapy

Two types of pressure treatments

Simple desiccation and Lyophilization

Desiccation that inhibits metabolism (2)

Reduce water activity

Inhibits metabolism and can cause lysis

Simple Desiccation

Drying

Reduce water activity

Addition of salt or water

Lyophilization

Rapid freezing under vacuum

Simple desiccation, reduce water activity, lyophilization

Three types of desiccation treatments

Sonication

Cavitation (formation of empty space) disrupts cells, lysing them

HEPA Filtration

Physically removes microbes from air

Membrane filtration

Physically removes microbes from liquid solutions

Ionizing radiation

Exposure to X-Rays or gamma rays

Ionizing radiation

Alters molecular structures, introduces double-strand breaks into DNA

Nonionizing radiation

Exposure to ultraviolet light

Nonionizing radiation

Introduces thymine dimers, leading to mutations

Photoreactivation

The “light” repair mechanism- thymine dimer covalent bonds cut photolyases

Excision repair

The “dark” repair mechanism- Damage nucleotides removed and repaired by multiple enzymes