Microbiology

Created by rajivrajkumar1 

Upgrade to
remove ads

Chapter 5 1. Understand the differences between the following: a. Sterilization, Disinfection, Pasteurization, Decontamination, Degerming, Sanitized, Preservation 2. What are the five situational considerations discussed in class? What are the approaches to control discussed for each? 3. What are the six requirements of a good disinfectant? 4. What five factors should be considered when choosing and antimicrobial procedure? 5. What are the five physical methods of control discussed in class? How…

Sterilization

-Removal of all microorganisms
▪Sterile item is absolutely free of microbes, endospores and viruses
-Can be achieved through filtration, heat, chemicals and irradiation

Disinfection

-Eliminates most pathogens
▪Some viable microbes may exist
▪Disinfectants = used on inanimate objects and surfaces
▪Antiseptics = used on living tissues

Pasteurization

▪Eliminates most pathogens
▪Some viable microbes may exist
▪Disinfectants = used on inanimate objects and surfaces
▪Antiseptics = used on living tissues

Decontamination

▪Treatment to reduce pathogens to level considered safe to handle

Degerming

▪Mechanism used to decrease number of microbes in an area, particularly the skin.

Sanitized

▪Implies a substantially reduced microbial population that meets accepted health standards
-Does not denote a specific level of control

Preservation

▪Process used to delay spoilage of perishable items
-Often includes the addition of growth-inhibiting ingredients or adjusting storage conditions

What are the five situational considerations discussed in class

Depends on situation and degree of control required
1. Daily life
2. Hospital
3. Microbiology laboratories
4. Food and food production facilities
5. Water treatment

What are the approaches to control discussed for each?

▪It is likely NO disinfectant meets all of these criteria!
▪Selection of Antimicrobial Procedure
▪Selection of effective procedure is complicated
▪Ideal method does not exist
▪Each has drawbacks and procedural parameters

What are the six requirements of a good disinfectant?

▪Be fast acting even in the presence of organic substances
▪Be effective against all types of infectious agents without destroying tissues or acting as a poison if ingested
▪Easily penetrate material to be disinfected without damaging or discoloring the material
▪Be easy to prepare and stable even when exposed to light, heat or other environmental factors
▪Be inexpensive and easy to obtain and use
▪Not have an unpleasant odor

What five factors should be considered when choosing and antimicrobial procedure?

1. Type of microbe
2. Extent of contamination
▪Number of organisms
3. Environment
4. Risk of infection
5. Composition of infected item

Type of Microorganism

-Most critical consideration
▪Is organism resistant or susceptible to generally accepted methods?
▪Resistant microbes include
Bacterial endospores
>>Resistant to heat, drying and numerous chemicals
-Protozoan cysts and oocysts
>>Generally excreted in feces and cause diarrheal disease
-Mycobacterium species
Cell wall structure initiates resistance
▪Pseudomonas species
>>Can grow in presence of many chemical disinfectants
-Naked viruses
>>Lack envelope and are more resistant to chemical killing

Number of Organisms Initially Present

-Time it takes to kill it directly affected by population size
▪Large population = more time

-Commercial effectiveness is gauged by decimal reduction time (D value)
▪Time required to kill 90% of population under specific conditions
-Washing reduces time required to reach disinfection or sterilization

Environmental Conditions

▪pH
-Most chemicals are more effective at lower pH

▪Temperature
-Most chemicals are more effective at higher temperature

▪Presence of organic materials
-Effectiveness can be hampered by the presence of organic molecules
>>Can interfere with penetration of antimicrobial agent
>>Vomit, Diarrhea, Blood...

Potential Risk of Infection

Medical items are categorized according to potential risk of disease transmission
▪Critical items = come in contact with body tissues
▪Semicritical instruments = contact mucous membranes but do not penetrate body tissues
▪Non-critical instruments = contact unbroken skin only
-Show little risk of transmission

Composition of the Item

-Some sterilization and disinfection methods are inappropriate for certain items

▪Heat is inappropriate for plastics and other heat sensitive items
▪Moist heat corrodes metals
▪Irradiation may damage plastics but works well on metals
▪Bleach should not be used on colorfast materials
▪Bleach should not be used on colorfast materials

What are the five physical methods of control discussed in class? How is each performed, and what is each used for?

1.Moist Heat
Boiling
Pasteruization
Autoclaving
2. Dry Heat
Incineration
Dry heat ovens
3. Filtration
Fluids vs. Air
4. Radiation
Ionizing vs. Ultraviolet
5. High Pressure

What are the five physical methods of control discussed in class? How is each performed, and what is each used for?

1.Moist Heat
Boiling
Pasteruization
Autoclaving
2. Dry Heat
Incineration
Dry heat ovens
3. Filtration
Fluids vs. Air
4. Radiation
Ionizing vs. Ultraviolet
5. High Pressure

Heat as Control

▪Heat treatment most useful for microbial control
-Relatively fast, reliable, safe and inexpensive
▪Heat can be used to sterilize or disinfect
▪Methods include
-Moist heat
-Dry heat

1.Moist Heat

▪Boiling
▪Pasteruization
▪Autoclaving

Boiling

▪(100° C)
-Destroys most microorganisms and viruses
-Not effective means of sterilization
▪Does not destroy endospores

Pasteruization

Pasteur developed to avoid spoilage of wine
Does not sterilize but significantly reduces organisms
Used to increase shelf life of food
Most protocols employ HTST method
Heated to 72°C and held for 15 seconds
Other protocol UHT
Heated to 140°C - 150°C, held for several seconds then rapidly cooled
Commercial Canning of Food
Moist Heat
Pressurized steam

Autoclaving

used to sterilize using pressurized steam
Heated water  steam  increased pressure
Preferred method of sterilization
Achieves sterilization at 121°C and 15psi in 15 minutes
Effective against endospores
Flash autoclaving sterilizes at 135°C and 15psi in 3 minutes
Prions destroyed at 132°C and 15psi for 4.5 hours

2. Dry Heat

...

Dry heat

Not as effective as moist heat
Sterilization requires longer times and higher temperatures
200°C for 1.5 hours vs. 121°C for 15 minutes

Incineration

method of dry heat sterilization
Oxidizes cell to ashes
Used to destroy medical waste and animal carcasses
Sterilizing inoculation loop
Glass petri dishes and pipets

Filtration

Membrane filtration are employed to remove microbes from fluids and air

Filtration
Fluids

Used for heat-sensitive fluids
Membrane filters allow liquids to flow through
Depth filters trap microbes using electrical charge

Filtartion of Air

Used for heat-sensitive fluids
Membrane filters allow liquids to flow through
Depth filters trap microbes using electrical charge

Radiation

Electromagnetic radiation
Range of wavelength is electromagnetic spectrum

Radiation can be ionizing or non-ionizing

Ionizing radiation

Radiation able to strip electrons from atoms
Three sources
Gamma radiation
X-rays
Electron accelerators
Causes damage to DNA and potentially to plasma membrane
Used to sterilize heat resistant materials
Medical equipment, surgical supplies, medications
Some endospores can be resistant

Ultraviolet

Non-ionizing radiation
Only type to destroy microbes directly
Damages DNA
Causes thymine dimers
Used to destroy microbes in air, drinking water and surfaces
Limitation
Poor penetrating power
Thin films or coverings can limit effect

High pressure

processing
Used in pasteurization of commercial foods
Does not use high temperatures
Employs high pressure
Up to 130,000 psi
Destroys microbes by denaturing proteins and altering cell membrane permeability

What are the three sites of chemical action discussed in class? Understand how each of these actions kill the bacterial cell. What is the most susceptible phase of growth?

...

What are the three sites of chemical action discussed in class?

...

What are the chemical methods of microbial control discussed in class? What points are important to consider when choosing a chemical agent?

...

How are the following used when preserving perishable products?

▪Preservation extends shelf life of many products
-chemicals are often added to prevent or slow growth of microbes
▪Other methods include
-Low temperature storage
-Freezing
-Reducing available water

Chemical preservatives

▪Formaldehyde, Quats and phenols
-Weak organic acids often used as food preservatives
▪Benzoic, ascorbic and propionic acids
▪Used in bread, cheese and juice
-Nitrates and nitrites used in processed meats
▪Inhibits germination of endospores and growth of vegetative cells
▪Have been shown to be potent carcinogen

Temperature control

▪Low temperature storage
-Microbial growth is temperature dependent
▪Low temperatures slow down or stop enzymatic reactions of mesophiles and thermophiles
-Some psychrophiles still able to grow
-Freezing as means of food preservation
▪Essentially stops microbial growth
▪Irreversibly damages cell
-Kills up to 50% of microbes
>>Remaining cells still pose potential threat

Reducing water availability

▪Reducing water availability
-Decreasing water availability accomplished by salting or drying food
▪Addition of salt increases environmental solutes
-Causes cellular plasmolysis
▪Numerous bacteria can continue to grow in high salt environments
-Staphylococcus aureus can survive in high salt concentrations
▪Desiccation or drying is often supplemented by other methods
Salting
▪Lyophilization (freeze drying)
Widely used to preserve foods like coffee, milk and meats

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set