Bacteriology Sterilization

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Sterilization

Back 1

- Destruction of all microbes, including endospores.
- Usually done by steam under pressure, or sterilizing gas

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Sanitization

Back 2

- Treatment that lower microbial counts to safe levels for public health purposes
- high temperature washing, or soaking in a chemical disinfectant.

Front 3

Disinfection

Back 3

- Destruction of vegetative pathogens
- physical or chemical methods --> Kills > 3 logs (decrease by 3 orders of magnitude)

Front 4

Decontamination

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- Reduction of pathogenic microbes to a levels where items are safe to handle.
- Elimination of Debris by cleaning.
- Prerequisite before disinfection of sterilization.

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Antisepsis

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- Destruction of vegetative pathogens on living tissue
- Always done with chemical antimicrobials.

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Parameters affecting disinfection/sterilization efficiency (4)

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1) Bacterial strain and form (vegetative -easier to kill vs. spore- harder to kill)
2) temperature (higher temp --> faster & more efficient killing) or disinfectant concentration
3) treatment duration (longer the treatment --> better chance to kill them)
4) initial concentration of cells and spores (easier to kill less)

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Why are vegetative cells more vulnerable?

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Vegetative cells or proliferating cells are doing DNA synthesis --> @ replicating fork there is single stranded DNA --> not protected by proteins --> vulnerable to mutations and breaks

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Why are spores harder to kill?

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Spores have a low H2O content --> high concentration of molecules in the cell and they become like crystals --> harder to denature
They are non-proliferating.

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Rate of microbial death by temperature is ____.

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constant --> logarithmic

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The ____ is important when considering microbial killing.

___ starting [] will end up with 0 cells faster than populations with _____ starting [] but both populations can be killed at the same rate.

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initial concentration of cells

Lower ... higher

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___ surrounded by ____ are most susceptible to disinfectant due to their changing ____.

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viruses ... lipids... fluidity

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____ have low level resistance to disinfectants.

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Vegetative (proliferative, metabolically active) bacteria

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____ have intermediate levels of resistance to disinfectants due to their proteins being ____ and low amounts of ____.

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non-lipid viruses... crystal-like... water

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____ have high level resistance to disinfectants for _____ reasons.

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Mycobacteria .... unknown

Front 15

____ are sterilants due to their ___ metabolic activity.

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Spores... low

Front 16

3 ways to estimate death by heat

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1) Thermal death point (TDP)
2) Thermal death time (TDT)
3) Decimal reduction time (D value)

Front 17

Thermal death point (TDP)

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lowest temperature at which all the microorganisms in a liquid suspension will be killed in 10 minutes

Front 18

Thermal death time (TDT)

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minimal length of time at which all bacteria in a liquid suspension wilol be killed at a given temperature

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Decimal reduction time (D value
MOST IMPORTANT!!

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time in which 90% of population will be killed at a given temperature. Gives accurate means to estimate how long and at what temp need to destroy an microorganism. Used in hospitals.

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T/F - D-value depends on initial concentration

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False

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(4)Physical methods of microbial control

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Filtration
Irradiation
Cold
Heat

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Physical methods of microbial control 1

Irradiation (2 forms)

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1) ionizing (gamma, X)- H2O-->hydroxyl radicals --> react with biological moelcules --> DNA!! High penetration
2) non-ionizing (UV)- absorbed and modifies DNA. Low penetration.

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Physical methods of microbial control 2

Cold

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Bacteriostatic!!!

Note: some bacteria do grow in the cold, but slowly.

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Physical methods of microbial control 3

Dry Heat (2 methods)

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Oxidation of macromolecules
- flaming: heating a metal to red glow--> fastest method
- hot air: heating in oven

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hot air sterilization: heat in oven @ ___ for ___ hours

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170 C ... 2

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Physical methods of microbial control 4

Moist heat (3 types)

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Moist heat: denaturation of macromolecules
-Pasteurization
-Boiling
-autoclave

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Moist Heat 1

Pasteurization

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heating at 63 C for 30 mins or 72 C for 15 secs --> sufficient to kill most microorganisms that cause food spoilage

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Moist heat 2

Boiling

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kills all vegetative forms of pathogenic bacteria and fungi within 10 minutes.

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Moist heat 3

Autoclave

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heating under pressure to temperatures above boiling.
121 C for 15 mins will kill ALL microbial forms.

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T/F- Moist heat is a more efficient sterilization method than dry heat

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True
H2O in the sample can change conformation of molecules

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Destruction of prions

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need high temp to completely denature because they are very stable structures.
133 C for 120-240 mins
180 C (dry heat) for 24 hrs

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____ (3) alter membrane permeability.

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alcohols
anionic detergents
phenols (at low conc.)

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____ (8) damages proteins and nucleic acids.

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aldehydes
biguanides
chlorine compounds
iodophors
oxidizing compounds
phenols (at high conc)
quaternary ammonium compounds
acridines

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Inhibition of membrane potentials / electron transport chain can be caused by _____ (3)

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bis-phenols
heavy metal derivatives
organic salts

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___ is a commonly used ____. It is a potent & broad spectrum microbicidal that targets membrane components, nucelic acids, and proteins. It ____ SH, hydroxyl, carboxyl, & amino groups. It is used to ______.

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Disinfectant
Glutaraldehyde
alkylates.
disinfect medical eqiupment

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____ is a strong oxidizer that attaches to ____ (3). It has ___ levels of toxicity to humans. It acts as a ___

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H2O2
lipids, DNA, and proteins
low
disinfectant

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___ is the most commonly used antiseptic. ___ enhances its activity and helps it denature ____.

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Alcohol
H2O
Proteins

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____ are also commonly used antiseptics. It will release ___. It is less effective in the presence of ____. It is released ___ so it acts for a ___ time.

Back 38

Iodophors
I2
blood
Slowly
longer

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Alcohol & Iodophors are useful against____. They both act pretty ____.

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Bacteria, fungi and viruses
rapidly (alcohol > iodophors)

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___ & ___ are used in hospitals before surgery to wash hands. Both have little effect on fungi.

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Tricloxan (no effect on viruses)
Chlorohexidine