Physical Methods Of Microbial Control

Front 1

Methods of Physical Control

Back 1

Physical methods to control microbial growth

- heat

- cold (not much in hospital, more food related)

- radiation

- drying/desiccation (food related)

- filtration

Front 2

Heat

Back 2

Most widely used method of microbial control

Temperatures that exceed a microbe’s max. growth temperature are microbicidal (kill)

Temperatures below the min. growth temperature are microbistatic (inhibit)

Front 3

Heat

Back 3

2 forms of heat are used:

- moist heat

- dry heat

Front 4

Heat

Microbial Resistance

Back 4

Low resistance

- bacterial vegitative cells

- fungi

Front 5

Heat

Microbial Resistance

Back 5

High resistance:
◦ Bacterial endospores (and prions)

– usually require temperatures above boiling
◦ Thermal death times vary

archaea - can tolerate extremely high

◦ archaea - can tolerate extremely high temperatures

Front 6

Heat

Microbial Resistance

Back 6

**need to consider optimal growth temps in organisms in order to determine resistance

Front 7

Heat

Thermal Death Measurements

Back 7

Thermal Death Times (TDT)

- shortest time required to kill a population of microorganisms at a specific temperature

(take culture, apply specific heat, keep checking what time was required to kill cells - they can no longer replicate underideal conditions)

Front 8

Heat

Thermal Death Measurements

Back 8

Thermal Death Point (TDP)
- lowest temperature required to kill all microbes in a liquid suspension in 10 minutes

- not used as often

Front 9

Moist Heat

Back 9

Temperature range 60°C to 135°C

Requires lower temperatures and shorter
exposure times

Causes denaturation of proteins

- impairs cellular metabolism

- interferes with DNA/RNA transcription

Front 10

Moist Heat

Back 10

Denaturation:

1. unravel of proteins

2. change binding sites

3. protein therefore wont be able to operate as normal

Front 11

Moist Heat

Methods of Control

Back 11

- steam under pressure **love in hospital

- non-pressurized steam (delicate equipment)

- boiling water (no application in hospital)

- pasteurization (food industry; also hospital)

Front 12

Moist Heat

Methods of Control: Steam Under Pressure

Back 12

Normal atmospheric pressure ~15 psi (raise pressure 2atm or to 30psi)

Steam must be pressurized to elevate
temperature above 100°C in order to sterilize

Increase pressure = increase boiling temp and increase temp of steam produced

Front 13

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 13

Sterilization chamber which allows the use of steam under pressure to sterilize

Increases in pressure beyond the “common combination” yields no significant decrease in exposure time and can damage the materials being processed

Front 14

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 14

***- most commom combination - 15psi above normal (2atm) and 121°C for 15-20 minutes ***

Front 15

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 15

Considerations:

Steam must reach surface of item being sterilized

Item must not be heat or moisture sensitive

Front 16

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 16

Considerations:

Mode of action denaturation of proteins, destruction of membranes and DNA

Load to allow evacuation of air and circulation of steam

Front 17

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 17

Sterilization achieved when steam condenses against objects in chamber and raises their temperature

Processing times depend on:

- bulk of load

-fullness of the chamber

*think of washing machine

Front 18

Moist Heat

Methods of Control: Steam Under Pressure

Autoclave

Back 18

Used to clean:

- glassware

- cloth (surgical dressings)

- metallic instruments (stainless steal only - rust)

- liquids

- paper (never seen)

- some media (culturing - medium to grow)

- some heat-resistant plastics

Front 19

Moist Heat

Methods of Control: Non-Pressurized Steam

Back 19

Used for substances that cannot withstand
the high temperatures of the autoclave

Front 20

Moist Heat

Methods of Control: Non-Pressurized Steam

Tyndallization

Back 20

Tyndallization: fractional (intermittent) sterilization designed to destroy spores indirectly

Front 21

Moist Heat

Methods of Control: Non-Pressurized Steam

Tyndallization

Back 21

Preparation exposed to flowing steam for 30 to 60 minutes, then a mineral is introduced to permit spore germination (max 100°C)

- germination makes endospore turn back into vegetative state

Resultant vegetative cells then destroyed by repeated steaming (strong ones can survive)

Front 22

Moist Heat

Methods of Control: Boiling Water

Back 22

Used for disinfection only as temperature does not exceed 100°C

30 minute exposure will kill most non-spore forming pathogens (e.g., staph, TB)

Front 23

Moist Heat

Methods of Control: Boiling Water

Back 23

Disadvantage

- items easily re-contaminated when removed from water bath

Not used for sterilization in hospital

Front 24

Moist Heat

Methods of Control: Pasteurization

Back 24

Heat treatment of perishable fluids destroys sensitive vegetative cells

Does NOT kill endospores or thermoduric microbes

Front 25

Moist Heat

Methods of Control: Pasteurization

Back 25

Followed by rapid chilling

- inhibits growth of survivors

- prevents germinationof spores

Used for anesthesia masks, endotracheal blades in hospital; also for milk, apple juice

Front 26

Moist Heat

Methods of Control: Pasteurization

Back 26

Ultrahigh temperature (UHT) – liquid exposed to 138°C for a fraction of a second

- less likely to change taste/nutrients

Batch method / high temperature short time (HTST)

- liquid exposed to 63°C for 30 minutes, then cooled to 4°C

Front 27

Dry Heat

Back 27

Air with a low moisture content, heated by
flame or an electric heating coil (basic oven)

Temperature ranges from 160 to 170°C for 2
to 4 hours

Front 28

Dry Heat

Back 28

Mode of action:

- dehydrates the cell

- impairs cellular metabolic reactions

- alters protein structure (inactivates)

◦ NB: lack of water can stabilize some protein
configurations ∴ higher temperatures will be
needed for microbial control

Front 29

Dry Heat

Hot Air Oven

Back 29

Incineration most rigorous of all heat treatments

Kills by:

- oxidation of cellular components

- increased concentration of toxic constituents

- denaturation of enzymes and other proteins

Front 30

Dry Heat

Hot Air Oven

Back 30

Process
- Preheat oven

- Load to allow circulation of air

- Cycle times vary 12 minutes to 4 hours at temperatures between 160-170°C +

Front 31

Dry Heat

Hot Air Oven

Back 31

Used for heat-resistant items that do not sterilize well with moist heat

ex: non stainless steal

- glassware (closed)

- powders

- glycerol

Front 32

Cold

Back 32

Microbiostatic: slows/inhibits growth of microbes but does not kill so not used in hospital often

Refrigeration 0-15°C and freezing <0°C

Used to preserve food, media and cultures

Front 33

Desiccation

Back 33

Drying process: gradual removal of water from cells, leads to metabolic inhibition

Not effective microbial control → many cells retain ability to grow when water is reintroduced

Lyophilization: freeze drying; preservation

Front 34

Filtration Methods

Back 34

Physical removal of microbes by passing a gas or liquid through filter

Used to sterilize heat sensitive liquids and air in hospital isolation units and industrial clean rooms

Front 35

Filtration Methods

Back 35

Includes:

- membrane filters

- HEPA filters

Front 36

Filtration Methods

Membrane Filters

Back 36

Thin membranes of cellulose acetate, polycarbonate or other plastic materials

Absorb very little of the fluid being filtered

Pore size carefully controlled and standardized

Vary from coarse (8 µm) to ultrafine (0.01µm)

Front 37

Filtration Methods

Membrane Filters

Back 37

Smallest pore sizes produce sterile filtrate

Must be collected in a sterile container

Front 38

Filtration Methods

Membrane Filters

Back 38

Negative pressure required to draw liquids through filter (vacuum)

Filters can be used to culture bacteria separated from liquid sample

Front 39

Filtration Methods

HEPA Filters

Back 39

High efficiency particulate air filters

Can be used to filter respiratory and anesthetic gases

Air entering/leaving isolation units, operating suites, laboratories

Front 40

Filtration Methods

HEPA Filters

Back 40

99.7% effective in filtering particals greater than or equal to 0.3µm

Front 41

Radiation

Electromagnetic Radiation

Back 41

- Energy in the form of waves transmitted through a material
- Includes ionizing and non-ionizing radiation

- energy content inversly related to wavelength the shorter the wavelength the higher the energy

Front 42

Radiation

Electromagnetic Radiation: Ionizing

Back 42

High energy radiation of very short wavelength

Sufficient to cause ionization of molecules
- Splits molecules into atoms/groups of atoms
- Splits water molecules into hydrogen ions and hydroxyl radicals (highly reactive)
- Radicals destructive to DNA and cell proteins
- Acts directly on vital cell components

Front 43

Radiation

Electromagnetic Radiation: Ionizing

Back 43

Includes:

- X-ray rays

- gamma rays

- electron beams

Front 44

Radiation

Electromagnetic Radiation: Ionizing

Back 44

Able to penetrate packaging and products and sterilize their interiors

Gamma rays least expensive ∴ used often
- Shielding required for the safety of the operators

Front 45

Radiation

Electromagnetic Radiation: Ionizing

Back 45

Used in cold sterilization of:

- plastic ware

- gloves

- syringes

- sutures

- IV sets

Front 46

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 46

Little penetrating power

Results in the formation of new covalent bonds, altering protein structure

Front 47

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 47

Items must be directly exposed

- passes readily through air

- slightly through liquids

- poorly through solids

Never achieve sterilization but can be used to clean air

Front 48

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 48

UV light creates pyrimidine dimers (new bond sulfur group)

- interferes with DNA reproduction

- inhibition of growth

- cellular death

Front 49

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 49

Ultraviolet radiation ranges in wavelength from 100-400nm
- Most lethal range 240-280nm (peak 260nm)

Front 50

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 50

Used to reduce the # of microorganisms in:

- air and on surfaces in OR

- laboratory biological safety cabinets

- transparent fluids

- vaccines

Front 51

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 51

Usual source is germicidal lamp (254 nm)

Germicidal lamps can decrease airborne microbes by 99%

Can also be used in the treatment of water and other liquids

Front 52

Radiation

Electromagnetic Radiation: Non-Ionizing

Back 52

Disadvantage: damaging effects on human tissues (what melanoma is caused by)

Front 53

Indicators of Sterilization

Back 53

- mechanical controls

- chemical controls

- biological controls

Indicators can be direct or indirect

Front 54

Indicators of Sterilization

Mechanical Controls

Back 54

Print-out of temperatures, pressures, times obtained in autoclave

Software programmed into machine

Important in quality control/quality assurance

Indirect indicator of sterilization

Front 55

Indicators of Sterilization

Chemical Controls

Back 55

A colour change will occur if chemical is held at a specific temperature for specific amount of time

Used in conjunction with mechanical controls

Indirect indicator of sterilization

Front 56

Indicators of Sterilization

Biological Controls

Back 56

Spores used (vial with nutrient strip)

Vial placed in deepest load of the autoclave

Large loads require more than one vial

Vial contains spore strip and nutrient medium

Front 57

Indicators of Sterilization

Biological Controls

Back 57

If sterilization is not achieved, spores will become vegetative cells and reproduce

Only direct indicator of sterilization (if doesn't grow)