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complete destruction of all forms of microbial life


destroys most microbial life, reducing contamination on inanimate surfaces. Does not kill spores


destroys most microbial life, reducing contamination on a living surface


the mechanical removal of most microbes from an animate or inanimate surface

Physical Agents

DRY - incineration or dry oven=sterilization or moist-steam under pressure=sterilization or boiling water, hot water and pasteurization-disinfection. RADIATION - Ionizing: x-ray, cathode, and gamma=sterilization or nonionizing: UV=disinfection

Chemical Agents

Gases: sterilization or disinfection
Liquids: Animate-antisepsis or inanimate-disinfection or sterilization

Mecanical Removal Methods

Filtration: Air and liquid both decomination

What are the primary targets od microbial control

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

What are the contaminants that need to be controlled

Bacterial vegetative cells and endospores (so resistant, the goal is sterilization)
Fungal hyphae and spores
Protozoan trophozoites and cysts


to kill

Name some "cides" and their functions

Bactericide: chemical that destroys bacteria (not endospores)
Fungicide: a chemical that can kill fungal spores, hyphae, and yeasts
Virucide: a chemical that inactivates viruses
Sporicide: can destroy bacterial endospores
Germicide and microbicide: chemical agents that kill microorganisms

Stasis and static

To stand still

name and functions of some statics

Bacteristatic: prevent the growth of bacteria
Fungistatic: inhibit fungal growth
Microbistatic: materials used to control microorganisms in the body, for example

what are some concerns with microbial control

*Does the application require sterilization, or is disinfection adequate?
*Is the item to be reused or permanently discarded?
*If it will be reused, can it withstand heat, pressure, radiation, or chemicals?
*Is the control method suitable for a given application?
*Will the agent penetrate to the necessary extent?
*Is the method cost- and labor-efficient, and is it safe?

Microbial death

sustained metobolic or structural damage to the point of losing the ability to reproduce.

Factors that Influence the Action of Antimicrobial Agents

1)The number of microorganisms
2)The nature of the microorganisms in the population
3)The temperature and pH of the environment
4)The concentration of the agent
5)The mode of action of the agent
6)The presence of solvents, interfering organic matter, and inhibitors

How do antimicrobial agents work against the cell wall

blocking synthesis, digesting it, breaking down its surface, or cell becomes fragil and is lysed easily

How do antimicrobial agents work against the cell membrane

surfactants (polar molecules) lower the surface tension of the cell membrane

How do antimicrobial agents work against the cells Protein and Nucleic Acid Synthesis:

Binds to ribosomes to stop translation, binds irreversibly to DNA preventing transcription and translation, or mutagenic agents

How do antimicrobial agents work against the cells Protein function

Some modes affect the binding sites of the substate be denaturation by breaking down some of the secondary or tertiary bonds causing complete unfolding, random bonding or incorrect folding or interfering with binding


elevated temperature (exceeding maximum growth temperature


lower temperatures (below the minimum growth temperature)

2 physical states of heat

Dry and moist

Forms of moist heat and the temps and times to kill

Hot and boiling water or steam. ranging from 60 C and 135 C

121C 15 min
125C 10 min
134C 3 min

Forms of dry heat and the temps and times to kill

flame or electric coil 160C to thousands of degrees
121C 600 min
140C 180 min
160C 120 min
170C 60 min

Thermal death time

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

Thermal death point

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

what are the practical concerns in the use of heat

* Temp and length of exposure
* Higher temps generally shorter ecposure; lower temps generally require longer exposure
* Thermal Death time
* Thermal Death Point

Common Methods of Moist Heat Control

1) Steam under pressue
2) Nonpressurized steam
3) Pasteurization
4) Boiling water

Steam under pressure

auto clave, pressure cooker, steam under pressure is hotter than free flowing steam or boiling proportional to the amount of pressure. Increased pressure enables temperature to be higher. At normal atmospheric pressure (15 psi) water boils at 100C and stema is the same temp, at higher pressures steam is hotter. 20 psi steam is 109C


intermittent sterilization for substances that cannot withstand autoclaving. Sterilize materials with 100C steam for 30 min.incubate 23-24 hours treat again repeat for 3 consecutive days with incubation periods,


* Used to disinfect beverages
*Heat is applied to liquids to kill potential agents of infection and spoilage, while retaining the liquid's flavor and food value
*Special heat exchangers
-Flash method: expose to 71.6°C -for 15 seconds
*Batch method: expose to 63°C to 66°C for 30 minutes
*Does not kill endospores or thermoduric microbes

boiling water

disinfection. single processing will not kill all resistant cells but will kill most non-spore forming pathogens including resisitant species. Major drawback is that items can be recontaminated after it leaves the water.

dry heat

direct flaming, incineration, hot air sterilization.

Dry Oven

*Usually an electric oven
*Coils radiate heat within an enclosed compartment
*Exposure to 150°C to 180°C for 2 to 4 hours
*Used for heat-resistant items that do not sterilize well with moist heat

Cold and Desiccation

* To slow growth of cultures and microbes in food during processing and storage
* Cold does not kill most microbes; freezing can actually preserve cultures
* 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

Are microbes adeversley affected by cold temps

Some are but most are not, some freezing temps actually preserve cultures.


energy emitted from atomic activities and dispersed at high velocity through matter or space

which forms of radiation are used for microbial control

Gamma rays - most penetrating
X rays - intermediate
Ultraviolet radiation - least penetrating

ionizing radiation

Fast-moving alpha or beta particles or high-energy radiation (gamma rays) emitted by radioisotopes. They have enough energy to dislodge one or more electrons from atoms they hit, forming charged ions in tissue that can react with and damage living tissue. Compare nonionizing radiation.

advantages to Ionizing radiation

speed, high penetrating power, and absence of heat

disadvantages to ionizing radiation

main one is potential dangers to machine operators from exposure to radiation and [ossible damage to some materials

nonionizing radiation

excites electrons and causes them to make new covalent bonds, which affects the 3-D structure of Proteins and Nucleic acids

characteristics of UV rays

*Wavelength approximately 100 nm to 400 nm
*Germicidal lamp: 254 nm
*Not as penetrating as ionizing radiation
*Powerful tool for destroying fungal cells and spores, bacterial vegetative cells, protozoa, and viruses

Applications of UV rays

*Usually disinfection rather than sterilization
*Hospital rooms, operating rooms, schools, food prep areas, dental offices
*Treat drinking water or purify liquids

what are the filters made from

thin membranes of cellulose, acetate, polycarbonate, and a variety of plastics

applications of filtration

*Prepare liquids that can't withstand heat
*Can decontaminate beverages without altering their flavor
*Water purification
*Removing airborne contaminants (HEPA filters)

forms of chemical agents

liquid, gaseous, or solid


solutions dissovled in alcohol or water-alcohol

why choose 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
*Sanitizing and deodorizing properties
*Affordability and ready availability

Factors that Affect the Germicidal Activity of Chemicals

*Nature of microorganisms being treated
*Nature of the material being treated
*Degree of contamination
*Time of exposure
*Strength and chemical action of the germicide

what is the concentration and exposure times for chlorine to kill mycobacterium, entamoeba cysts and Hepatits A?

Myco: 50 ppm in 50 secs
Enta: 0.1 ppm in 150 min
Hepatits 3ppm in 30 mins

what is the concentration and exposure times for Ethyl Alcohol to kill S. aureus, E coli and polio

S. Aureus: 70% 10 min
E.coli: 70% 2 min
polio 70% 10 min

what is the concentration and exposure times for Hydrogen Peroxide to kill S. Aureus, Gonorrhoeae and herpes

S. aureaus: 3% at 12.5 secs
Gonorrhoeae: 3% at 0.3 secs
Herpes: 3% at 12.8 secs

what is the concentration and exposure times for Quantery ammonium compound to kill S. Aureus and Salmonella

s. aureus: 450 ppm at 10 min
salmonella 300 ppm at 10 min

what is the concentration and exposure times for Ethylene Oxide Gas to kill Strep and Influenza

Strep: 500 mg/1 for 2.4 min
Flu: 10,000 mg/1 for 25 h

Halogen Antimicrobial Chemicals

*Fluorine, bromine, chlorine, and iodine group VII on periodic table
*Microbicidal and sporicidal with longer exposure
*1/3 of anitmicrobial agents are halgoens

Chlorine compounds:

liquid and gaseous chlorine, hypochlorites, chloramines
*Kills bacteria and endospores
*Also kills fungi and viruses
*Example: Household bleach

Iodine compounds

free iodine and iodophors
*Topical antiseptic

Phenol coefficient

compares a chemical's antimicrobic properties to those of phenol

what do low and hig concentrations of phenol do to a microbe

Low: inactivate certain critical enzyme systems
High: cellular poisons

most widely used phenolic



*Complex organic base containing chlorine and two phenolic rings
*Targets cell membranes and protein structure
*At moderate to high concentrations, it is bactericidal for both gram-positive and gram-negative bacteria but inactive against spores
*Mild, low toxicity, rapid action

what are the only alochol anitmicrobial agents sutible for microbial control?

isopropyl and ethyl alochols

What does an alcohol antimicrobial agent depend on?

concentration (50-95% typically)

What can and can't alcohol antimicrobial agents destroy

cannot destyor spores but can destroy resistant vegetative forms

What are alcohol anitmicrobial agents most effective on inactivating: Enveloped or non-enveloped viruses


What are dermicdal effects due to?

direct and indirect actions of oxygen

What does oxygen form that is toxic?

Hydroxl free radicals

What does hydogen peroide kill

bacteria, viruses and fungus

Can hydrogen peroxide kill spores?

in high concentrations yes

What do detergents act as?


Which is more powerful anionic or cationic detergents?

Cationics are genrally more effective, anionics are limited

What are detergents

polar molecules with a positively charged head and at least one long uncharged hydrocarbon chain. the head contains a central nitrogen nucleus with various alkyl

What are the heavy metal compounds used?

Hg, Ag, Au, Cu, As, and Zn

which heavy metals are still used?

Hg and Ag

oligodynamic action

the ability of very small amounts of heavy metals to exert antimicrobial activity

How do heavy metals work?

inds to functional groups of proteins and inactivates them

What are the drawbacks to using metals in microbial control

*Can be very toxic to humans
*Often cause allergic reactions
*Large quantities of biological fluids and wastes neutralize their actions
*Microbes can develop resistance to them

What are the 2 more common aldehydes

Glutaraldehyde and formaldehyde

What are aldehydes

-CHO functional group on the terminal carbon (strong reducing group)


* Yellow acidic liquid with an odor
* cross linking protein molecules on the cells surface
* amino acids are alkylated
* irreversibly disrupt the activity of enzymes within the cell


an irritating, acidic, gas used in laboratory disinfectants and preservatives

Gaseous Sterilants and Disinfectants

*Ethylene oxide (ETO)
*Propylene oxide
*Chlorine dioxide

Ethylene oxide

gas used to sterilize heat sensitive ingredients

Propylene oxide

alkylates proteins; sterilize heat sensitive items

Chlorine dioxide

effective, rapid-acting environmental surface disinfectant or chemical sterilant.

what is the primary source used in certain drugs for chemotherapy


what are some aniline dyes and what are they used for

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

What are some yellow acridine dyes and what are they used for

acriflavine and proflavine sometimes used for antisepsis and wound treatment

Why aren't dyes used very often

they have limited applications because they stain and have a narrow spectrum of activity

why are acids and alkalis limited in applications

they are corrosive, caustic and hazardous in nature

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