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Exam 2


the killing or removal of ALL microorganisms in a material or on an object


the reduction of the number of pathogenic microorganisms to the point where they pose no danger of disease


a chemical agent that can safely be used externally on living tissue to destroy microorganisms or to inhibit their growth


a chemical agent used on inanimate objects to destroy microorganisms. Most disinfectants do not kill spores.


a chemical agent typically used on food-handling equipment and eating utensils to reduce bacterial numbers so as to meet public health standards. Sanitization may simply refer to thorough washing with only soap or detergent

Bacteriostatic Agent

an agent that inhibits the growth of bacteria


an agent that kills bacteria. Most such agents do not kill spores


an agent that inactivates viruses


an agent that kills fungi


an agent that kills bacterial endospores or fungal spores


free from infection or pathogens; the actions practiced to make and maintain an object free from infection or pathogens.


removal of microbes from a limited area, such as the skin around an injection site


inhibition of fungi


inhibiting the growth of fungi without destroying them




(suicide, homicide)

General conditions influencing control of microorganisms

temperature, type of MO, environment, physiological state of MO

How does temperature influence control of microorganisms?

When heat is applied to a material, the death rate of the organisms in or on it remains logarithmic but is greatly accelerated. Slow freeze and cell walls burst.

How does the type of microorganism influence control?

Different antimicrobial agents affect various species of bacteria and their endospores differently.

How does the environment influence control of microorganisms?

Things like pH, soaps and detergents, surfactants, acids, alkalis, presence of heavy metals, alcohols, halogens, phenols, oxidizing agents, alkylating agents, dyes, etc can affect the environment.

How does the physiological state of microorganisms influence control?

Any given species may be more susceptible to an antimicrobial agent at one phase of growth than at another. The most susceptible phase for most is the logarithmic phase, because that is when many enzymes are actively carrying out synthetic reactions and interfering with even a single enzyme might kill the organism.


Most effective and economical method of control

Thermal Death Point

the temperature that kills all the bacteria in a 24-hour-old broth culture at neutral pH in 10 minutes

Thermal Death Time

the time required to kill all the bacteria in a particular culture at a specified temperature.

Decimal Reduction Time

also known as DRT or D Value - the length of time needed to kill 90% of the organisms in a given population at a specified temperature

Name three types of moist heat

boiling water, steam under pressure and pasteurization

Boiling water

destroys vegetative cells and most bacteria and fungi and inactivates some viruses. It cannot be used on items that are moisture or heat sensitive

Steam Under Pressure

kills spores, as well as vegetative organisms, and disrupts the structure of nucleic acids in viruses. It cannot be used for items that are moisture or heat sensitive.


kills pathogens, especially Salmonella and Mycobacterium, that might be present in milk, other dairy products and beer. Some pathogens have still been found in pasteurized milk and cheeses

What are the conditions for the autoclave?

120*C and 15 psi for 15-20 minutes

What are precautions for the autoclave?

Must remove all of the air
Steam must come into direct contact with whatever you are sterilizing.
Wrap items in cloth or paper
Caps on bottle must be loose

Dry Heat

like oven - high heat long time; not good for liquids, plastic, can add incineration; it is the only suitable means of sterilizing oils and powders


will remove things - essentially is going to catch small stuff
Excellent way to sterilize liquids and gases, especially those sensitive to heat

Why is a refrigerator bacteriostatic?

extends life of food by slowing growth -STATIC technique = inhibits growth

Slow Freeze

kills MO (water freezes expands and bursts cell well)

Flash Freeze/Quick Freeze

preserves MO

Which is more effective in controlling growth, fast freeze or slow freeze? Why?

Slow freeze is more effective in controlling MO because it kills the MO opposed to flash or fast freeze preserving it.


drying can be used to preserve foods because the absence of water inhibits the action of enzymes

Osmotic Pressure

High concentrations of sugar or salt to preserve foods - draws water out of the organism and dehydrates/kills

Ionizing Radiation

Gamma rays and/or Xrays
- can dislodge electrons from atoms, creating ions
- kill MO and viruses; Used to sterilize foods
- referred to as a high energy particles

Nonionizing Radiation

UVA, UV, Lasers, Microwave
- damages DNA {thymine dimers}
- low energy particles

How are Thymine Dimers formed?

Radiation damages DNA
Damages two adjacent T strands
Thymine dimer - distorts the thymine base pair

Unless this damage is repaired - cell dies very quickly

What factors must be considered when choosing a disinfectant?

Short or long time to work
How long it takes to penetrate an organism to kill it/ how long to penetrate an object
Most chemicals have to be prepared in a very precise manner/ too dilute or too much is not necessarily a good thing - too concentrated can adversely affect - Preparation - temperature
Odor - phenol can be very irritating, lysol, formaldehyde.
Microbe range - types of MOS and their sensitivity - not all chemicals affect all MOs in the same way - some more effective than others etc
Specific application - type of object or surface to treat/environment - living vs inanimate
Presence of biological/organic material - plant material, food, body fluids - blood, urine, sputum, vomit, feces, semen, vaginal secretions
How active is the MO - dormant spore, etc. Less active is harder to destroy

What are the 3 ways that disinfectants harm or kill microorganisms?

Damage membranes
Inhibit enzymes
Inhibit metabolic processes

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