micro #11

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micro #1

primary targets of microbial control

MO capable of causing infection or spoilage that are constantly present in the environment & on humans

Contaminants that need to be controlled

1. Bacterial vegetative cells and _endospores_ (so resistant, the goal is sterilization - b/c so resistant spores)
2. Fungal hyphae and spores
3. Yeasts
4. Protozoan trophozoites and cysts
5. Worms
6. Viruses
7. Prions - just protein w/ability to fold, influence other proteins & can return to functioning form

Prions

protein w/ability to fold, influence other proteins & can return to functioning form

Sterilization

1. Removes all _viable__ microorganisms including viruses
2. Material is said to be sterile
3. Usually reserved for inanimate objects
4. Mostly performed with heat (moist heat)
5. Sometimes chemicals called _sterilants_ are used

Disinfection

step down from sterilization
1. The use of a physical process or chemical agent (_disinfectant_) to destroy vegetative pathogens
2. Does not destroy bacterial endospores
3. Usually used only on inanimate objects
4. Also removes toxins (toxins are proteins - physically removed or denatured)
5. 5% bleach solution

Decontamination

1. Used when actual sterilization isn't needed but need to decrease the risk of infection or spoilage (ex. food industry)
2. _Sanitization_: any cleansing technique that mechanically removes microorganisms to reduce contamination to safe levels
3. Sanitizer: compound such as soap or detergent that sanitizes
4. Sanitary: may not be free from microbes but are safe for normal use
5. _degermation_: reduces the numbers of microbes on the human skin (ex. alcohol wipes)

what is microbial death?

1. When various cell structures become _dysfunctional__ and the entire cell sustains irreversible damage
2. If a cell can no longer function under ideal environmental conditions
3. Death begins when a certain threshold of microbicidal agent is met, and continues in a _logarithmic_ manner (exponential death - usually 90% killed in 1st treatment, then keep going)

Factors that Influence the Action of Antimicrobial Agents

1. The _number_ of microorganisms
2. The _nature_ of the microorganisms in the population (what can they withstand)
3. The temperature and pH of the environment
4. The _concentration_ of the agent (usually an increase of agent then more antimicrobial)
5. The mode of action of the agent
6. The presence of solvents, interfering organic matter, and inhibitors
7. Biofilms - communities of MO. have to remove the biofilm

How Antimicrobial Agents Work: Their Modes of Action

1. The Cell Wall = good target for bacteria
a. The cell becomes fragile and is lysed easily
b. Damage the can be done: (21)
1. blocking its synthesis
2. digesting it (lysozyme, penicillin)
3. breaking down its surface
2. The Cell Membrane - loosen membrane. bad can get in and good can get out. surfactant molecules disrupt lipid bilayer. cell membrane makes up the envelope. if you take away envelope then you can't get into the cell

Protein and Nucleic Acid Synthesis

1. Binding to _ribosomes_ to stop translation
2. Bind irreversibly to _DNA_ preventing transcription and in turn translation
3. Mutagenic agents
☼ Examples: (Table 9.3) gamma rays, UV (cause thymine dimers) or X-ray

Methods of Physical Control

1. Heat as an Agent of Microbial Control
a. Generally, elevated temperatures are microbicidal and lower temperatures are microbiostatic
b. Can use moist heat or dry heat
☼ Think about:
☼ Florida in the summer
☼ Humidifier on your furnace
☼ What do these have in common? Moist makes heat penetrate. helps drive heat in

Thermal Death Measurements

1. Temperature and length of exposure must be considered
2. Higher temperatures generally allow shorter exposure times; lower temperatures generally require longer exposure times
3. _Thermal death rate_ (TDT): the shortest length of time required to kill all test microbes at a specified temperature
4. _thermal death point_ (TDP): the lowest temperature required to kill all microbes in a sample in 10 minutes

Moist Heat: Steam under pressure

1. Pressure raises the temperature of steam
2. _autoclave_ is used
3. Most efficient pressure-temperature combination for sterilization: 15 psi which yields 121°C
-increase loads then increase time

Moist Heat: Pasteurization

1. Used to disinfect beverages
2. Heat is applied to liquids to kill potential agents of infection and spoilage, while retaining the liquid's flavor and food value
3. Special heat exchangers (_equivalent_ treatments)
A. Batch method/Classic pasteurization is 63°C to 66°C for 30 min
B. Flash method/High temp, short time (HTST): expose to 71.6°C for 15 seconds
C. Ultra high temperature (UHT): 140°C for <1 sec
4. Does not kill endospores or _thermoduric_ microbes

Moist Heat: Boiling water

1. For disinfection and not _sterilization__
2. Expose materials to boiling water for 30 minutes

Dry Heat: Hot Air and Incineration

1. Incineration
a. Ignites and reduces microbes to ashes and gas
b. Common practice in microbiology lab: inoculating loop
Can also use tabletop infrared incinerators

Dry Heat: Dry oven

1. Usually an electric oven
2. Coils radiate heat within an enclosed compartment
3. Exposure to 150°C to 180°C for 2 to 4 hours (longer exposure)
4. Used for heat-resistant items that do not sterilize well with moist heat

The Effects of Cold and Desiccation

1. To _slow_ growth of cultures and microbes in food during processing and storage
2. Cold does not kill most microbes; freezing can actually preserve cultures
3. Desiccation: _dehydrate/dessicate_ of vegetative cells when directly exposed to normal room air
4. Lycophilization: a combination of _freezing_ & _drying_; used to preserve microorganisms and other cells in a viable state for many years

Radiation as a Microbial Control Agent

1. Radiation: energy emitted from atomic activities and dispersed at high velocity through matter or space
2. For microbial control:
a. Gamma rays
b. X rays
c. Ultraviolet radiation
-inanimate surfaces
-short wave length more penetration & damage

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