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the destruction of all microbial life, Removes all viable microorganisms including viruses, Sterile, for inanimate objects, Sometimes chemicals called sterilants are used


destroys most microbial life, reducing contamination on inanimate surfaces, Physical process or chemical agent to destroy vegetative pathogens,toxins, does not kill endospores, 5% bleach


destroys most microbial life, reducing contamination on a living surface (ex. wash hands) applied directly to exposed body surfaces to destroy or inhibit vegetative pathogens (iodine)


the mechanical removal of most microbes from an animate or inanimate surface (ex. cleaning horse stalls), decreases the risk of infection or spoilage, Sanitation, Sanitizer, Sanitary, Degermation

Microbial Control Methods

physical agents, chemical agents, mechanical removal methods

Types of Physical Agents

heat, radiation

Types of Heat

dry: incineration (sterilization), dry oven (sterilization)

Types of Radiation

steam under pressure (sterilization), Boiling water, hot water, pasteurization (disinfection)

Types of Chemical agents

gases: (sterilization, or disinfection) liquid: animate (antisepsis), inanimate (disinfection or sterilization)

Types of Mechanical removal

filtration: air (decontamination), liquids (decontamination)

Contaminates that need to be controlled

bacterial vegetative cells and endospores, fungal hyphae and spores, yeasts, protozoan trophozoites and cysts , worms, viruses, prions

Primary Targets of Microbial Control

Microorganisms that can cause infection or spoilage that are constantly present in the external environment.


the growth of microorganisms in the blood and other tissues


any practice that prevents the entry of infectious agents into sterile tissues (gloves, mask, wash hands)

The agents Verses the Process

cide=to kill; stasis and static=to stand still


chemical that destroys bacteria (not endospores)


a chemical that can kill fungal spores, hyphae, and yeasts


a chemical that inactivates viruses


can destroy bacterial endospores

Germicide and Microbicide

chemical agents that microorganisms


prevent growth of bacteria


inhibit fungal growth


materials used to control microorganisms in the body, for example


any cleansing technique that mechanically removes microorganisms to reduce contamination to safe levels


compound such as soap or detergent that sanitizes


may not be free from microbes but are safe for normal use


reduces the numbers of microbes on the human skin (alcohol wipes)

Microbial death

when cell structures become dysfunctional and has irreversible damage, call no longer reproduce in good conditions, logarithmic manner

How Antimicrobial Agents work

blocks its synthesis, digest it, break down its surface( by osmotic shock), makes the cell membrane fragile and sled easily

Protein and Nucleic Acid Synthesis

binding to ribosomes to stop translation, bind irreversibly to DNA preventing transcription and transaction, mutagenic agents

Methods of physical control

heat as an agent of microbial control -generally elevated temperature are mi

Thermal Death Time (TDT)

the shortest length of time required to kill all test microbes are a specified temperature

Thermal Death Point (TDP)

the lowest temperature required to kill all microbes in a sample in 10 minutes

Steam Under Pressure

Pressure raises the temperature combination for sterilization: 15 psi which yields 121*C (will not kill prions)

Non-pressurized Steam

intermittent sterilization or tyndallization- expose to free flowing steam fro 30-60 minutes, incubate fro 23-24 hours, treat again; repeat for 3 days in a row


used to disinfect beverages to kill potential agents of infection and spoilage, two methods: flash method, batch method (does not kill endospores or thermoduric microbes)

Flash Method

expose to 71.6*C fro 15 seconds (does not kill endospores or thermoduric microbes)

Batch Method

expose to 63-66*C fro 30 minutes (does not kill endospores or thermoduric microbes)

Boiling Water

for disinfection and not sterilization, expose materials to boiling water for 30 minutes

Dry Heat: Hot Air and Incineration

reduces microbes to ashes and gas- bunsen burner, tabletop in fared incinerators

Dry Oven

exposure to oven at 150-180*C for 2-4 hours- used for resistant items that do not sterilize well with moist heat

The Effects of Cold and Desiccation

slows growth of cultures and microbes in food, does not kill most microbes; freezing can actually preserve cultures- two types: Desiccation, Lyophilization


dehydration of vegetative cells when directly exposed to normal room air


a combination of freezing and drying; used to preserve microorganisms and other cells in a viable state for many years


energy emitted from atomic activities and dispersed at high velocity. gamma rays, x rays, ultraviolet radiation

Ultraviolet Radiation

damages DNA and kills it, disinfection rather than sterilization, used for hospital rooms , schools, drinking water

Decontamination by Filtration: Techniques for Removing Microbes

removes microbes from air and liquid , fluid strained through a filter with openings large enough for fluid but too small fro microorganisms, filters are thin membranes of cellulose acetate, polycarbonate , and a variety of plastic materials

Applications of Filtration

liquids that cant withstand heat, can decontaminate beverages without altering their flavor, water purification, removing airborne contaminants (HEPA filters)


solutions dissolves in pure alcohol or water- alcohol mixtures

Choosing a Microbicidal Chemical

rapid action even in low concentrations, solubility in water or alcohol and long-term stability, broad-spectrum microbicidal action without being toxic to human and animal tissues, penetration of inanimate surfaces to sustain a cumulative or persistent action, resistance to becoming inactivated by organic matter, noncorrosive or nonstaining properties

Halogen Antimicrobial Chemicals

fluorine, bromine, chlorine, and iodine

Chlorine Compounds

liquid and gaseous chlorine, hypochlorites, chloramines: kills bacteria, endospores, fungi, and viruses (ex. household bleach)

Iodine Compounds

free iodine and iodophors: topical antiseptic, disinfectant

Phenol Coefficient

compares a chemical;s anti-microbic properties to those of phenol: high concentrations-cellular poisons, lower concentrations- inactivate certain critical enzyme and systems (denatures proteins)

Alcohols as Antimicrobial Agents

ethyl and isopropyl are suitable fro microbial control, does not destroy bacteria and spores at room temperature but can destroy resistant vegetative forms- more effective in inactivating enveloped viruses

Alcohol concentration 50-70%

dissolve membrane lipids, disrupt cell surface tension, and compromise membrane integrity

Alcohol concentration 50-90%

denatures proteins through coagulation; but higher concentration does not increase microbial activity

100% Absolute Alcohol

dehydrates cells and inhibits their growth

Hydrogen Peroxide and Related Germicides

germicidal effects are due to the direct and indirect actions of oxygen, oxygen forms hydroxyl free radicals which are highly toxic and reactive to the cells, bactericidal, virucidal, and fungicidal, in higher concentrations it is sporicidal


act as surfactants, anionic detergents have limited microbicidal power, cationic detergents are more effective because the positively charged end binds well with the predominantly negatively charged bacterial surface proteins (destroys membrane)

Heavy Metal Compounds

Hg, Ag,Au, Cu, As, Zn, only Hg and Ag still have significance as germicides, Oligodynamic action, bind onto functional groups of proteins and inactivating them, Drawbacks: can be very toxic to humans, can cause allergic reaction, large quantities of biological fluids and wastes neutralize their actions (pus), microbes develop resistance to them

Oligodynamic Action

having antimicrobial effects in exceedingly small amounts

Aldehydes as Germicides

-CHO functional group on the terminal carbon (gas), Glutaraldehyde and formaldehyde (formalin- aqueous solution)- most often used for microbial control

Dyes as Antimicrobial Agents

certain drugs used in chemotherapy, Two types: Anukube dyes, Yellow acridine dyes (limited applications because they stain and have a narrow spectrum of activity)

Aniline Dyes

crystal violet and malachite green- are very active against gram-positive species of bacteria and various fungi

Yellow Acridine Dyes

acriflavine and proflavine- sometimes used for antisepsis and wound treatment

Acids and Alkalis

very low or high pH can destroy or inhibit microbial cells, limited in applications due to their corrosive, caustic, and hazardous nature (preservatives ex. vinegar)

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