Microbiology Chapter 09: Physical and Chemical Control of Microbes

Comprehensive vocabulary flashcards covering microbial control definitions, resistance hierarchies, physical and chemical control methods, cellular targets, and clinical decontamination categories from Chapter 09.

Sterilization

A process that destroys or removes all viable microorganisms, including viruses and bacterial endospores; strictly reserved for inanimate objects.

Disinfection

A physical process or chemical agent that destroys vegetative pathogens and removes microbial toxins from materials, but does not destroy bacterial endospores; normally used on inanimate objects.

Decontamination (Sanitization)

A cleansing technique that mechanically removes microorganisms and other debris to reduce contamination to safe public health levels, commonly applied to eating and cooking utensils.

Antisepsis (Degermation)

The application of chemical agents directly to exposed body surfaces, wounds, and surgical incisions to destroy or inhibit vegetative pathogens.

Relative Resistance Hierarchy

The spectrum of microbial resistance to control agents, ranging from the most resistant forms (prions and bacterial endospores) down to the least resistant forms (enveloped viruses such as SARS-CoV-2).

Bacterial Endospores

Microbial survival structures traditionally considered the most resistant microbial entities; destroying them is the primary goal and benchmark of sterilization.

Bactericide

A chemical agent that destroys vegetative bacteria, but is not effective against bacterial endospores.

Sporicide

A chemical agent capable of destroying bacterial endospores, effectively acting as a sterilant.

Sepsis

The growth and proliferation of microorganisms in the blood and other normally sterile body tissues.

Asepsis

Any practice that prevents the entry of infectious agents into sterile tissues, thereby preventing infection.

Bacteristatic Agent

A chemical agent that inhibits the growth and multiplication of bacteria on tissues or environmental objects without directly killing them.

Microbial Death

The permanent loss of reproductive capability in microorganisms, even under optimum growth conditions.

Surfactants

Polar molecules, such as detergents, that bind to and disrupt the lipid layer of cytoplasmic membranes, allowing vital ions to leak out and damaging chemicals to enter.

Moist Heat

Heat delivered via hot water, boiling water, or steam at temperatures between $60^\circ\text{C}$ and $135^\circ\text{C}$, which operates by coagulating and denaturing cellular proteins.

Dry Heat

Heat delivered via hot air or an open flame at temperatures ranging from $160^\circ\text{C}$ to several thousand degrees Celsius, which dehydrates cells, denatures proteins, and oxidizes cell components into ashes.

Thermal Death Time (TDT)

The shortest length of time required to kill all test microbes in a sample at a specified temperature.

Thermal Death Point (TDP)

The lowest temperature required to kill all microbes in a sample in exactly $10\,\text{min}$.

Autoclaving

A moist heat sterilization method utilizing steam under pressure (typically $121^\circ\text{C}$ for $15\,\text{min}$) to elevate temperature above boiling and kill endospores.

Pasteurization

A moist heat disinfection technique that applies heat to liquids to reduce microbial load and destroy pathogens while preserving flavor and nutritional value.

Incineration

A dry heat sterilization method using an intense open flame or furnace to ignite and reduce microbes and contaminated materials to ashes and gas.

Hot-Air Oven

A dry heat sterilization chamber that circulates heated air at $150^\circ\text{C}$ to $180^\circ\text{C}$ for $2$ to $4\,\text{hours}$ to destroy endospores and sterilize glassware and metallic instruments.

Desiccation

The gradual dehydration of vegetative cells exposed to room temperature air, which kills some microbes but merely preserves many others.

Lyophilization

A preservation method combining instantaneous freezing and vacuum drying that removes water to prevent ice crystal formation, keeping cultures viable for many years.

Ionizing Radiation

Highly penetrating radiation (gamma rays, X rays, cathode rays) that sterilizes heat-sensitive materials by causing deep atomic ionization and DNA breakage.

Nonionizing Radiation

Low-penetration ultraviolet (UV) radiation that acts as a surface disinfectant by exciting atoms and inducing abnormal bonding in DNA.

Thymine Dimer

An abnormal cross-link formed between adjacent thymine bases in DNA caused by ultraviolet (UV) radiation, which disrupts replication and transcription.

Membrane Filtration

A mechanical physical control method that strains fluids through microscopic pore openings too small for microbes to pass, enabling true sterilization of heat-labile liquids.

HEPA Filters

High-efficiency particulate air filters used to mechanically decontaminate air by trapping microbes in hospital rooms and sterile enclosures.

Osmotic Pressure Control

A preservation and disinfection technique that uses high concentrations of salt or sugar to create a hypertonic environment, causing bacterial plasmolysis.

High-Level Germicides

Chemical sterilants capable of destroying all vegetative microbes, fungal spores, viruses, and resistant bacterial endospores.

Intermediate-Level Germicides

Chemical disinfectants that destroy vegetative fungal spores, viruses, and all bacteria—including Mycobacterium tuberculosis—but do not kill bacterial endospores.

Low-Level Germicides

Chemical disinfectants that eliminate vegetative bacteria, fungi, and some viruses, but cannot destroy Mycobacterium tuberculosis or bacterial endospores.

Critical Medical Equipment

Medical devices expected to come into contact with sterile body tissues or the vascular system, requiring complete sterilization.

Semicritical Medical Equipment

Medical devices that come into contact with mucous membranes or non-intact skin, requiring high-level disinfection to eliminate vegetative pathogens.

Noncritical Medical Equipment

Medical devices that contact only intact skin (e.g., blood pressure cuffs), requiring only low-level disinfection.

Halogens

Chemical antimicrobial agents (such as chlorine and iodine) that oxidize proteins and nucleic acids, acting as sterilants at high concentrations but being rapidly inactivated by organic matter.

Phenolics

Intermediate-level antimicrobial agents that disrupt lipid membranes and denature proteins; they remain active in organic matter and hard water but can irritate tissue.

Aldehydes

Potent high-level chemical sterilants (such as glutaraldehyde and formaldehyde) that inactivate microorganisms by alkylating and cross-linking protein and nucleic acid molecules.

Ethylene Oxide

A toxic and flammable chemical gas that alkylates proteins and nucleic acids, used to sterilize temperature- and moisture-sensitive medical equipment.

Colonization

The persistent establishment and multiplication of microorganisms on or in body tissues such that they become part of the resident normal flora.

Contamination

The temporary presence of transient microbes picked up from the environment that do not establish permanent residency on or in host tissues.