Microbiology Chapter 7

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95 terms · The Control of Microbial Growth

Aseptic Surgery

--technique to prevent microbial contamination of surgical wounds

--hand washing most important


--the removal or destruction of ALL living microorganisms including endospores

--HEATING is the most common method for killing microbes

--done by steam under pressure, sterilizing gas


--a sterilizing agent

--liquid or gases can be sterilized by filtration

Commercial Sterilization

--limited heat technique used in sterilizing canned food

--not completely sterilized as it would degrade the food
--only heated enough to destroy the endospores of Clostridium botulinum-produces deadly toxin

At what temperature would canned food spoil?

above about 45*C


--used to treat NONLIVING surfaces or substance i.e. tables, counters, etc.----disinfectant

--destroy harmful microorganism usually the destruction of vegetative (non-endospore-forming) pathogens

--by way of chemicals, UV radiation, boiling water, or steam


--the treatment of LIVING tissue---antiseptic

--by way of chemical


--technique used when preparing someone for an injection with the swabbing of the skin with alcohol

--does NOT kill the bacteria just MOVES them out of the way


--technique used in restaurants to clean glassware, china, and tableware

--intended to lower microbial counts to safe public health levels and prevent spread of disease

--high temperature of dish washing and or dip in chemical


--names of treatments that cause the outright death of microbes

--meaning "kill"

A biocide, or germicide

--kills microorganisms (except endospores)

--example: fungicide kills fungi, virucide inactivates viruses

-stat or -stasis

--inhibit the growth and multiplication of bacteria

--meaning "to stop" or "to steady"


--inhibits growth of bacteria

--once a bacteriostatic agent is removed growth might resume


--from the Greek for decay or putrid, indicates bacterial contamination

--septic tanks for sewage treatment


--the absence of significant contamination

--Aseptic--sanitize--means that an object or area is free of pathogens

Antimicrobial Chemicals

--used to heat or treat bacterial populations making then die at a constant rate

The Number of Microbes
*influence of antimicrobial treatment

--the more microbes there are to begin with, the longer it takes to eliminate the entire population

Environmental Influences
*influence of antimicrobial treatment

--presence of organic matter often inhibits the action of chemical antimicrobials (i.e. blood, vomit, feces)

--disinfectants work somewhat better under warm conditions
*heat speeds up reaction

--heat works better in acidity then in alkaline conditions

Time of Exposure
*influence of antimicrobial treatment

--chemical antimicrobials often require extended exposure to have better effectiveness

--more resistant microbes or endospores--have to be in chemicals longer to work

Microbial Characteristics
*influence of antimicrobial treatment

--affect the choice of chemical and physical control methods

What is located just INSIDE the cell wall and is the target of many microbial control agents?

plasma membrane
--regulates the passage of nutrients into the cell and elimination of wastes from the cell

Functional properties of proteins are the result of their __________

--Tertiary Structure
-maintained by chemical bonds linking portions of amino acid chains folded
-some of these bonds are held by hydrogen bonds, which or weak & break by heat or certain chemicals----resulting in the denaturation of the protein

Physical Methods of Microbial Control include the following:

---Heat ---High Pressure
---Moist Heat Sterilization ---Desiccation
---Pasteurization ---Osmotic Pressure
---Dry Heat Sterilization ---Radiation
---Filtration ---Low Temperature


--kills microorganism by denaturing their enzymes

________ is the lowest temperature at which all the microorganisms i a particular liquid suspension

--Thermal Death Point (TDP)

--killed in 10 minutes

________the minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature

Thermal Death Time (TDT)

Decimal Reduction Time (DRT, or D value)

--is the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed

Moist Heat Sterilization

--kills microorganisms primairly by coagulating proteins (denaturation)
-caused by breakage of hydrogen bonds in the protein

Types of Moist Heat Sterilization

1) BOILING-kills vegetative forms of bacterial pathogens, almost viruses, and fungi w/ their spores in < 10 mins

2) STEAM-(unpressurized) same temp as boiling water, doesn't destroy as quickly as boiling
-some hepatitis can survive >30 mins
-some bacterial endospores > 20 hours

What is the preferred method of sterilization?

AUTOCLAVE-steam under pressure
-no used for material that can be damaged by heat or moisture

--large industrial autoclaves are called RETORTS

An autoclave can kill all organisms and their endospores in about 15 mins but not ________


---water is the conductor for heat
---the higher the pressure the higher the temperature


--Louis Pasteur-method of preventing spoilage of beer & wine

----intent is to eliminate pathogenic microbes

--Thermoduric bacteria survive pasteurization but unlike to cause disease or milk to spoil

What is the purpose of the phosphatase Test?

--to determine whether the process of pasteurization was carried out correctly
-phosphatase is an enzyme naturally found in milk

--heating is less efficient in foods that are more viscous and fats in food can have a protective effect on microorganisms

Milk pasteurization today uses termerautres of at least 72*C only for 15 seconds. This is called what?

High-Temperature Short-Time Pasteurization (HTST)
--milks flows by a heat exchanger
--lowers total bacterial counts-->so milk keeps well

Sterilized Milk is also called dried milk. How is this done?

Ultra-High-Temperature (UHT) treatment
--stored for several months w/o refrigeration
--milk DOES NOT touch the heat
--sprayed thru a nozzle to a chamber filled with high-temp steam under pressure to convey the heat to the milk

Equivalent Treatments

--occurs as the temperature is increased, much less time is needed to kill the same number of microbes

What is the simplest method of dry heat sterilization?

-kills by oxidation effects

Examples: heating loop till red, incineration

Hot-Air Sterilization

--another form of dry heat sterilization

--done in oven at 170*C for 2 hours


--used to sterilize heat-sensitive materials, such as culture media, enzymes, vaccines, and antibiotic solutions

HEPA Filters

-High-efficiency particulate air (HEPA)
--removes all microorganisms larger than about 0.3um in diameter

--used to filter air like in operating rooms

Membrane Filters

--composed of cellulose esters, plastic polymers, have become popular industrial use--usually 0.1 mm thick

--pores filter 0.22um and 0.45um bacteria sizes

--filters with pores as small as 0.01um will retain viruses and seven some large protein molecules

What is the temperature of ordinary refrigerators?


Low Temperatures that effect microorganisms depend on_____ and _____.

--the specific microbe and the intensity of the application

--the metabolic rate of most microbes is so reduced that they cannot reproduce or synthesize toxins
-thus reason we refrigerate food-stop bacteria growth
--has a bacteriostatic effect

What can grow slowly at refrigerator teomperatures and will alter the appearance and tast of foods over time?


Is fast freeze of slow freeze more harmful to bacteria?


--rapid freezing tender microbes dormant but not killing them

High Pressure does not work on what type of bacteria?


High Pressure Technique

--applied to liquid suspended bacteria
--i.e. fruit juices-advantage is to preserve the flavors, color, and nutrient values

Desiccation is the absence of _______.


True/False: Microorganisms cannot grow or reproduce in the absence of water?


--can remain viable for years however
--once water is available they can resume growth adn division

Viruses are generally resistant to desiccation but not as resistant as ________.

BACTERIAL ENDOSPORES--which have been know to survive for centuries

Osmostic Pressure

--is used to preserve foods with the use of high concentrations of salts and sugars

--hyPERtonic environment-water leaves the cell

What are more capable then bacteria to grow in materials with low moisture or high osmotic pressure?


---molds rather then bacteria causes spoilage of foods and able to form mildew on a damp shower curtain

Ionizing Radiation

--gamma rays, x rays, high energy beams

--have a wavelength SHORTER then that of nonionizing radiation (less then 1nm)

--destroys DNA of cells, thus killing them

Gamma Rays

--emitted by certain radioactive elements such as cobalt

--produced by accelerating electrons to high energies in special machines

--penetrate deeply but may require hours to sterilize large masses


--produced by machines in a manner similar to the producton of electron beams

High-Energy Electron Beams

--have much lower penetrating power

--requires only a few seconds of exposure

Uses of Ionizing Radiation

--processing spices, certain meats and vegetables

--sterilize pharmaceuticals, disposable dental, and medical supplies

--against bioterrorism
-postal service often uses electron beam radiation to sterilize certain classes of mail

Nonionizing Radiation

--has a wavelength LONGER then that of ionizing radiation (greater than 1mn) - has less energy

--best example is UV light

Functions of UV light

--damages the DNA of exposed cells by causing bonds to form usually the thymines in the DNA chains

--most effective for killing microorganisms about 260nm

--used to control microbes in the air
-germicidal lamps used in hospitals

--to disinfect vaccines and other medical products

Disadvantages of UV light as a disinfectant

--the radiation is not very penetrating, so the organisms to be killed must be directly exposed to the rays

--can damage human eyes, and prolonged exposure can cause burns and skin cancer in humans


--do NOT have a DIRECT effect on microorganisms

--bacteria can readily be isolated from the interior of recently operated microwaves

How do microwaves kill bacteria?

Moisture containing foods are heated by microwave action, and the heat will most vegetative pathogens.

Use-Dilution Test

-currant standard to evaluate the effectiveness of disinfectants and antiseptics

Steps for the Use-Dilution Test

**the effectiveness of the disinfectant is determined by the number of cultures that grow

1) metal/glass (8mmx10mm) dipped into standardized cultures of the test bacteria grown in liquid media
2) removed
3) dried at 37*C for a short time
4) place into a solution of the disinfectant at recommended concentration
5) left there for 10 mins at 20*C
6) transfer to a medium that permits the growth of any surviving bacteria

Disk-Diffusion Method

-used in teaching laboratories to evaluate the efficacy of a chemical agent

Steps for the Disk-Diffusion Method

1) a disk of filter paper is soaked with a chemical
2) then placed on an agar plate that has been previously inoculated and incubated with the test organism

*after incubation, if the chemical is effective, a clear zone representing inhibition of growth can be seen around the disk


--disrupt plasma membrane, denaturation of enzymes

--rarely used, except as a standard of comparison

--seldom used as a disinfectant or antiseptic because it irritates the skin and has a bad odor


--disrupt plasma membrane, denaturation of enzymes

--used for environmental surfaces, instruments, skin surfaces, and mucous membrane

--derivatives of phenol that are reactive even in the presence of organic material; )-phenylphenol is an example


--probably disruption of plasma membrane

--used as disinfect in hand soaps and skin lotions

--Triclosan is an especially common example of a bisphenol, broad spectrum, but most effective against gram-poistive

The removal or destruction of all forms of microbial life are called
A. sterilization
B. disinfection
C. pasteurization
D. sanitization

A. Sterilization

The destruction of vegetative pathogens is called
A. sanitization
B. commercial sterilization
C. disinfection
D. antisepsis

C. Disinfection

Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels
A. Sanitization
B. Sterilization
C. pasteurization

A. Sanitization

The Absence of significant contamination is called
A. Sepsis
B. bacteriostatsis
C. asepsis
D. antisepsis

C. Asepsis

Commercial sterilization is a limited heat treatment to destroy
A. Streptococcus pyogenes
B. Clostridium tetani
C. Staphylococcus aureus
D. Clostridium dotulinum endospores

D. Clostridium botulinum endospores

Which of the following BEST describes the pattern of microbial death?
A. the cells in a population die at a constant rate
B. all the cells in a culture die at one time
C. not all of the cells in a culture are killed
D. the pattern varies, depending on the species

A. the cells in a population die at a constant rate

The time it takes to kill a microbial population is
A. dependent on heat
B. proportional to the number of microbes
C. dependent on life cycle phases
D. dependent on chemicals

B. proportional to the number of microbes

The lowest temperature at which all of the microorganisms in a particular liquid suspension will be killed in 10 minutes is called
A. Thermal death point
B. Thermal death time
C. Decimal reduction time
D. Decimal reduction point

A. Thermal Death Point

Which of the following is the MOST resistant to chemical biocides?
A. prions
B. gram-positive bacteria
C. viruses without envelopes
D. vegetative protozoa

A. Prions

Which of the following is the BEST advertisement for a disinfectant?
A. kills E. coli
B. kills Staphylococcus aureus
C. kills Pseudomonas
D. kills lipophilic viruses

C. kills Pseudomonas

To sterilize heat-labile solutions, one should use
A. dry heat
B. autoclave
C. membrane filtration
D. pasteurization

C. membrane filtration

Which method kills microorganisms primarily by the coagulation of proteins (denaturation)?
A. filtration
B. radiation
C. desiccation
D. moist heat

D. moist heat

The phosphatase test is used to determine whether which of the following processes was carried out correctly by?
A. radiation
B. filtration
C. desiccation
D. pasteurization

D. Pasteurization

Flaming is one of the simplest methods of
A. pasteurization
B. dry heat sterilization
C. moist heat
D. desiccation

B. Dry Heat Sterilization

Which of the following methods causes destruction of DNA?
A. radiation
B. osmotic pressure
C. heat
D. desiccation

A. Radiation

Sterilization can be achieved by using
A. Alcohol
B. soap
C. cholrine
D. ethylene oxide

D. Ethylene Oxide

Which of the following substances is the LEAST effective antimicrobial agent?
A. Soap
B. phenolics
C. iodine
D. alcohol

A. Soap

The eradication of non enveloped viruses CANNOT be achieved by
A. chlorine
B. ozone
C. alcohol
D. ethylene oxide

C. Alcohol

Ethanol can be used as an effective bactericide when used at a concentration of
A. 70%
B. 50%
C. 40%
D. 100%

A. 70%

Which of the following is not used to preserve foods?
A. nisin
B. sodium nitrite
C. potassium sorbate
d. biguanides

D. Biguanides

Which of the following is the MOST useful for disinfecting medical instruments?
A. Quats
B. chlorine
C. phenol
D. benzoic acid

A. Quats

This was first used by Lister to control surgical infections in the operating room
A. alcohol
B. chlorhexidine
C. carbolic acid
D. mercuric chloride

C. Carbolic Acid

These chemical agents cause a disruption of the plasma membrane and denaturation of enzymes
A. Phenolics
B. biguanides
C. alcohols
D. halogens

A. Phenolics

These agents cause denaturation of enzymes and other essential proteins
A. aldehydes
B. heavy metals
C. peroxygens
D. nitrates

B. Heavy Metals

What Chemical is used to prevent molds from growing in cheese and soft drinks?
A. sorbic acid
B. calcium propionate
C. sulfur dioxide
D. sodium nitrate

A. Sorbic Acid

What chemical selectively inhibits certain iron-containing enzymes of Clostridium botulinum?
A. sodium benzoate
B. sodium nitrate
C. sodium nitrite
D. calcium propionate

C. Sodium Nitrite

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