Microbial Control Methods and Principles

Comprehensive vocabulary flashcards covering physical and chemical microbial control methods, biosafety levels, sterilization, radiation, and chemical disinfectant classes.

Fomites

Objects or materials that are likely to carry infection, such as clothes, utensils, and furniture.

BSL-1

Lowest risk biosafety level for microbes that are not known to cause disease in healthy hosts and pose minimal risk to workers and the environment.

BSL-2

Biosafety level for typically indigenous microbes that are associated with diseases of varying severity.

BSL-3

Biosafety level for indigenous or exotic microbes that cause serious or potentially lethal diseases through respiratory transmission.

BSL-4

Highest risk biosafety level for dangerous and exotic microbes that pose a high risk of aerosol-transmitted infections, frequently fatal without treatment or vaccines.

Five Common Microbial Control Protocols

Sterilization, sanitation, disinfection, antisepsis, and degerming.

Bactericide

A chemical that destroys vegetative bacteria but not endospores.

Bacteriostatic

Chemical agents that prevent the growth of bacteria.

High vs. Low Temperature Effects

High temperatures are generally lethal to microbes, whereas low temperatures are generally inhibitory.

Boiling

A simple and cheap moist heat method requiring at least $30\,\text{min}$ that does not kill all vegetative cells.

Pasteurization

A moist heat method applied at about $70\,^\circ\text{C}$ for $15\,\text{seconds}$ that is faster and better at killing than boiling and preserves food integrity, but does not kill endospores or thermodurics.

Autoclave

A true sterilization method that heats steam above $100\,^\circ\text{C}$ under increased pressure (typically $10\text{--}40\,\text{min}$ at $121\,^\circ\text{C}$); good for liquids and many solids, but unsuitable for plastics or styrofoam.

Incineration

A dry heat method reaching 1000s of degrees C that burns everything to ash and applies to a limited range of materials.

Hot Air Oven

A dry heat method running at $150\text{--}180\,^\circ\text{C}$ for $1\text{--}4\,\text{hours}$ that evaporates liquids and is slightly easier to use than an autoclave.

High Pressure (Microbial Control)

Kills vegetative cells by denaturing proteins (though endospores survive); utilized in methods such as hyperbaric oxygen therapy.

Desiccation

Dehydration of vegetative cells at normal room temperature, halting metabolic reactions due to lack of water; kills some species while others survive or are preserved by lyophilization (freeze drying).

Gamma Rays

A form of ionizing radiation that penetrates deeply into cells and shatters the DNA or RNA double helix.

X-rays (Microbial Control)

A form of ionizing radiation using streams of accelerated electrons to inflict severe, irreversible double-strand breaks in microbial DNA and disrupt cellular metabolism.

Ultraviolet (UV) Radiation

A non-ionizing radiation method (most effective at $260\,\text{nm}$ over long exposure times) that forms thymine dimers, blocking proper DNA replication and transcription to cause cell death.

Ionizing Radiation

Radiation effective at destroying all life by causing double-strand DNA breaks; penetrates solid surfaces (requiring thick lead or iron shielding), is dangerous for living human tissue, and does not transfer to food.

Air Filtration

A physical control method that removes airborne particles and contaminants to improve indoor air quality, protect machinery, and support health.

Liquid Filtration

A physical control method that separates suspended solids, impurities, and harmful contaminants from a fluid stream using a porous filter medium.

Aqueous Preparations

Chemical solutions where antimicrobial chemicals are dissolved in pure water as the solvent.

Tinctures

Chemical solutions where antimicrobial chemicals are dissolved in pure alcohol or water-alcohol mixtures.

Heavy Metals (Chemical Class)

Chemical agents that bind to sulfur groups of proteins and disrupt them; not classified as sterilants.

Halogens (Chemical Class)

Potential sterilants that include chlorine (denatures proteins and suspends metabolic reactions) and chloramine (releases chlorine more slowly; used in water purification).

Alkylating Agents

Potential chemical sterilants that disrupt microbial proteins in a variety of ways.

Peroxygens

Potential chemical sterilants that control microbes by introducing reactive oxygen species.

Alcohols (Chemical Class)

Chemical agents that disrupt cell membranes, viral envelopes, and proteins; not classified as sterilants.

Surfactants

Chemical agents that create small bubbles; not classified as sterilants.

Soap Micelle

A spherical cluster of soap molecules formed in water with grease-loving tails inside and water-loving heads facing out; removes or disrupts microbes via membrane disruption and mechanical removal.