CHP 13- STERILIZATION/DISINFECTION

Applied to non-living objects

disinfectants

Applied to living tissues

antiseptic

Killing/removal of all microorganisms (object)

sterilization

no living organisms or endospores

sterile

reducing the number of pathogenic organisms

disinfection

prevents microorganisms from growing

bacteriostatic

kills bacteria

bactericide

kills fungus

fungicide

kills many microbes but usually not spores

germicide

kills endospores/fungal spores

sporocide

kills viruses

virucide

What are the 3 principles of sterilization?

-A definite proportion of organisms die in a time interval

-The fewer organisms present, the shorter the time needed to achieve sterility

-Microorganisms differ in their susceptibility to antimicrobial agents.

What are the ways that heat kills microbes?

-Dry heat, moist heat, and pasteurization

oven; slow to penetrate, used for metal instruments, glassware, oils, and powders

dry heat

heat under pressure, maintain temp/pressure for a period of time; validation including tapes/documentation

autoclave

Treating a substance with heat to kill or slow the growth of pathogens

pasturization

4-5 Celsius; slows microbial growth

refrigeration

-20 Celsius, preserves food for longer periods of time; microbes can be frozen at -80 Celsius or in liquid Nitrogen

freezing

The absence of water inhibits microbial enzymes

drying

dried after being frozen; long term preservation of microbes

lyophilization

effectiveness ---> increased by high temperatures

can be affected by the concentration of the chemical, pH, and the time left on the microorganisms

(Ex: Ethyl/Isopropyl alcohol works best at 70% solutions because water is necessary to denature proteins)

chemical antimicrobial agents

How are chemical agents tested?

Phenol test/coefficient

using tiny filter paper disks, soaked in chemical agents, and put on agar plates inoculated with bacteria.

clear regions around the disks mean it kills local bacterial cells.

filter paper test

metal tube; coated in bacteria and dipped in different dilutions of chemical agents

Tube put into growth media to see if the bacteria grow

use-dilution test

How do chemical reagents work?

Denature proteins, affect membranes, affect nucleic acids, or affect energy production

(3D shape is destroyed) can be bacteriostatic or bactericidal

Denature proteins

break down lipids

affect membranes

How do detergents work?

They contain alkali/sodium; Cationic or Anionic charge

What are other things that inhibit microbial growth?

Acids/Bases, heavy metals, halogens, alcohols, phenol, oxidizing agents, dyes, alkalyzing agents

What are physical ways to control microbial growth

heat, cold, radiation, filtration, drying, and high pressure

Lactic/propionic acids used as food preservatives

Acids/Bases

silver, mercury, selenium

Heavy metals

chlorine, iodine, bromine

Halogens

Denatures proteins, cell membrane, dissolves lipids, but does NOT necessarily sterilize

Phenols

hydrogen peroxide; disrupts disulfide bonds in protein

Oxidizing agents

Disrupts proteins/nucleic acids (can cause cancer, formaldehyde)

Alkalyzing agents

Acridine orange stops cell replication, and methylene blue stops bacterial growth

-blocks cell wall synthesis and inhibits gram + growth

Dyes

The temperature that kills all bacteria in 24 hr old broth culture at neutral pH in 10 minutes.

Thermal Death point

The temperature required to kill all bacteria in a 24 hour old broth culture neutral pH in 10 minutes.

Thermal Death time

The time required to kill 90% of organisms at a particular temperature (EX: 150 Celsius = 30 Minutes)

Decimal Reduction time

UV light --> 40-390 nm

-200 nm = EFFECTIVE AGAINST MICROBES; Damages proteins

-Absorbed by nucleic acids, then damages them and can be used to repair enzymes

-Destroying viruses

-No penetration (useful for decontaminating air)

Radiation

X-Rays (0.1-4.0 nm); create ions in substances by dislodging electrons (Cobalt 60 used)

-Killing bacteria/viruses in foods and medical devices

Gamma Radiation

1 mm to 1m; only useful for sterilizing substances that contain water

microwave radiation

400-700 nm oxidizes certain bacterial enzymes

-certain dyes and increase the effect of strong light on microbes

visible light spectrum

What are other methods?

-ETO

-E-Beam

-Chlorine Dioxide Gas

-Filtration

-Osmotic Pressure

-Alkalating agent

-Disrupts cell metabolism

-Penetrates breathable packaging

Ethylene Oxide Gas (ETO)

-Uses Beta particles in inactive microbes

-Faster but not as much as penetration as Gamma

Electron Beam (E-Beam)

-Strong oxidizer

-Sterilizes medical devices, food, and public water

-Does NOT chlorinate

Chlorine Dioxide Gas

Passing material through a strainer to get rid of microbes

-Used when heat sterilization would harm the substance

-0.025-25

-0.2 filter commonly used to sterilize cultures from bacteria

Filtration

High concentrations of sugar/salt ---> cause plasmolysis (LOSS OF WATER)

-Leads to bacterial cell death

-Used in jellies and salted meats

Osmotic Pressure