Microbio Final: Week 9

Sepsis

bacterial contamination

Asepsis

the absence of significant contamination

surgery techniques prevent the microbial contamination of wounds

Sterilization

removing and destroying all microbial life

Commercial Sterilization

killing clostridium botulinum endospores in canned goods

Disinfection

destroying harmful microorganisms on inanimate surfaces or environments

Antisepsis

destroying harmful microorganisms from living tissue

Degerming

the mechanical removal or microbes from a limited area

Sanitization

lowering microbial counts on eating utensils to safe levels

Biocide (Germicide)

treatments that kill microbes

Bacteriostasis

inhibiting, not killing, microbes

Disinfectant Selection

1. must be fast acting in the presence of organic materials

2. must be effective against all microorganisms without destroying tissue or acting as a toxin if ingested

3. easily penetrate the material to be disinfected without discoloration or damage

4. easy to prepare and stable in the environment where it is to be used

5. inexpensive and easy to use

6. no unpleasant odor

there is no perfect disinfectant that meets all these criteria

Effectiveness of Treatment Depends On

number of microbes

environment (organic matter, temperature, biofilms)

time of exposure

microbial characteristics (endospores, cell wall)

Microbial Control Agent Actions

damage to plasma membrane

• causes leakage of cellular contents

• interferes with cell growth

damage to proteins (enzymes)

damage to nucleic acids

Denaturation

heat ruining or making proteins inactive

Thermal Death Point (TDP)

lowest temperature at which all cells in a liquid culture are killed in 10 mins

Thermal Death Time (TDT)

minimal time for all bacteria in a liquid culture to be killed at a particular temperature

Decimal Reduction Time (DRT)

minutes to kill 90% of a specific population of bacteria at a given time

Moist Heat Sterilization

causes coagulation and denaturation of proteins

boiling

free-flowing system

autoclaving

kills all organisms (except prions) and endospores

steam must contact the items surface

preferred method for sterilization in health care environments

Autoclave

steams under pressure

121*C at 15psi for 15 mins

Moist Heat Process

steam enters the steam chamber and expels air, chamber pressure and temperature build to the proper levels

after the appropriate time period, another valve opens to allow for steam to escape the chamber

bigger containers need longer sterilization times

tests strips are used to indicate sterility

Pasteurization

reduces spoilage organisms and pathogens in milks and juices

High Temperature Short Time (HTST)

72*C for 15 secs

Thermoduric

organisms survive, but are unlikely to cause disease or to spoil refrigerated milk

Ultra High Temperature Treatments (UHT)

will sterilize milk, creamer, and juice which can then be stored without refrigeration

rapidly heated to 140*C for 4 secs followed by rapid cooling

Dry Heat Sterilization

kills by oxidation

flaming, incineration, hot air sterilization

oven 170*C for 2 hours

Filtration

passage of substance through a screen like material

used for heat sensitive materials

High Efficiency Particulate Air (HEPA) Filters

remove microbes bigger than 0.3um in diameter

Membrane Filters

remove microbes bigger than 0.22um in diameter

pore sizes of as small as >0.05um are available which can filter out viruses and large proteins

Low Temperature Microbe Control

has a bacteriostatic effect

ex: refrigeration, deep freezing, lyophilization (freeze drying)

High Pressure Microbe Control

denatures proteins, alters carbohydrate structure

Dessication

absence of water prevents metabolism

Osmotic Pressure Microbe Control

uses high concentrations of salts and sugars to create a hypertonic environment

causes plasmolysis

Ionizing Radiation

ex: x-rays, gamma rays, electron beams

ionizes water to create reactive hydroxyl radicals

damages DNA by causing lethal mutations

used by food industry (spices, certain meats, vegetables)

sterilization of pharmaceuticals, disposable dental and medical supplies, mail

Gamma Rays

penetrate deeply but require hours to sterilize

High Energy Electron Beams

less penetration, but faster (in seconds)

Non-Ionizing Radiation

ultraviolet (260nm)

damages DNA by creating thymine dimers

UVC “germicidal” lamps used in hospital rooms, nurseries, operating rooms, and cafeterias

effective, but doesn’t penetrate, good for surfaces

must avoid contact with eyes and skin

ex: visible blue light

microwaves kill by heat, not especially antimicrobial

Visible Blue Light

470 nm

kills a wide range of bacteria due to the formation of a singlet oxygen

Sonication

high frequency ultrasound waves to disrupt cell structures

the disruption is achieved due to the rapid changes in pressure within the intracellular liquid