chap 3 Flashcards
Early civilizations practiced what to control microbial
growth.
salting, smoking, pickling, drying, and
exposure of food and clothing to sunlig
Sterilization:
destruction of all forms of microbial life including the most resistant forms (endospores)
Heating is the most common method used in sterilization
A sterilizing agent is called a sterilant
Commercial sterilization:
heat treatment of canned food required to destroy Clostridium botulinum that can produce a deadly toxin (that can cause constipation, muscle weakness, …)
It takes 25 minutes to destroy this bacteria at 100C.
Disinfection:
Control directed at reducing the number of pathogenic microorganisms to a point where they no longer cause diseases.
Usually refers to the removal of vegetative or non-endospore forming pathogens.
Chemicals, Ultraviolet radiation, boiling water, or steam.
Disinfectant: chemical used to treat inanimate objects or surfaces.
Antisepsis:
Disinfection directed at living tissues such as human skin and, especially, wounds.
Antiseptic:
chemical applied to a living tissue
Degerming:
Mechanical removal of most microbes in a limited area. Example: Alcohol swab on skin.
sanitization
Use of chemical agent on food-handling equipment to meet public health standards and minimize chances of disease transmission.
Example: Hot soap & water.
Pasteurization:
Use of heat to destr0y pathogens and to reduce the number of spoilage microorganisms in food and beverages
Biocide or Germicide:
An agent that kills certain microorganisms.
•Bactericide
An agent that kills bacteria (most do not kill endospores)
•Viricide:
An agent that inactivates viruses.
•Fungicide:
An agent that kills fungi.
•Sporicide:
An agent that kills bacterial endospores or fungal spores
Bacteriostatic Agent:
An agent that inhibits the growth of bacteria, but does not necessarily kill them.
Sepsis:
Comes from Greek for decay or putrid. Indicates bacterial contamination.
Aseptic techniques:
Used to prevent contamination of surgical instruments, medical personnel, and the patient during surgery.
Also used to prevent bacterial contamination in food industry.
Aseptic:
absence of pathogenic microbes
Factors Influencing Microbial Death
Several factors influence the effectiveness of antimicrobial treatment:
- Number of Microbes: The more microbes present, the more time it takes to eliminate population.
- Type of Microbes: Endospores are very difficult to destroy. Vegetative pathogens vary widely in susceptibility to different methods of microbial control.
- Environmental influences:Presence of organic material (blood, feces, saliva) tends to inhibit antimicrobials, pH etc.
- Time of Exposure:Chemical antimicrobials and radiation treatments are more effective at longer times. In heat treatments, longer exposure compensates for lower temperatures.
- Microbial characteristics: resistance genes, protective structures(e.g.capsules) caninhibitaction, bioflimsprevent penetration
heat (physical characteristics)
Kills microorganisms by denaturing their enzymes and other proteins. Heat resistance varies widely among microbes.
-Thermal Death Point (TDP):
Lowest temperature at which all of the microbes in a liquid suspension will be killed in ten minutes.
-Thermal Death Time (TDT):
Minimal length of time in which all bacteria will be killed at a given temperature.
-Decimal Reduction Time (DRT):
Time in minutes at which 90% of bacteria at a given temperature will be killed. Used in canning industry
Moist Heat Sterilization:
Kills microorganisms by coagulating their proteins (denaturation) and it requires temperatures above that of boiling water.
Boiling:
Heat to 100oC or more at sea level. Kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores within 10 minutes or less. Endospores and some viruses are not destroyed this quickly. However brief boiling will kill most pathogens.
Hepatitis virus: Can survive up to 30 minutes of boiling.
Endospores: Can survive up to 20 hours or more of boiling.
Autoclave
:Chamber which is filled with hot steam under pressure. Preferred method of sterilization, unless material is damaged by heat, moisture, or high pressure.
•Temperature of steam reaches 121oC at twice atmospheric pressure.
•Most effective when organisms contact steam directly or are contained in a small volume of liquid.
•All organisms and endospores are killed within 15 minutes.
•Require more time to reach center of solid or large volumes of liquid.
Autoclaving is used to sterilize culture media, instruments, dressings, intravenous equipment, applicators, solutions, syringes, transfusion equipment,
Pasteurization:
Developed by Louis Pasteur to prevent the spoilage of beverages.
Used to reduce microbes responsible for spoilage of beer, milk, wine, juices, etc.
Pasteurization is mild
heating that is sufficient to kill particular spoilage or disease organisms without seriously damaging the taste of the product.
Classic Method of Pasteurization:
Milk is exposed to 65oC for 30 minutes.
High Temperature Short Time Pasteurization (HTST):
Used today. Milk is exposed to at least 72oC for 15 seconds
Ultra High Temperature Pasteurization (UHT):
Milk is treated at 140oC for 3 seconds and then cooled very quickly in a vacuum chamber. Advantage: Milk can be stored at room temperature for several months.
Dry Heat:
Kills by oxidation effects.
Direct Flaming:
Used to sterilize inoculating loops and needles. Heat metal until it has a red glow.
Incineration:
Very effective to sterilize items like biological and clinical wastes, Paper cups, dressings ; however it’s the combustion of organic materials, so pathogens and some toxins are destroyed by incineration
Hot Air Sterilization:
Place objects in an oven. Require 2 hours at170oC for sterilization. Dry heat is less effective than moist heat.
Filtration
Removal of microbes by passage of a liquid or gas through a screen like material with small pores.
*Used to sterilize heat sensitive materials like vaccines, enzymes, antibiotics, and some culture media.
High Efficiency Particulate Air Filters (HEPA):
-Used in operating rooms and burn units to remove bacteria from air,
Remove almost all microorganisms larger than 0.3 μm in diameter
Membrane Filters:
Uniform pore size. Used in industry and research. Different sizes:
-0.22 and 0.45μm Pores: Used to filter most bacteria. Don’t retain spirochetes, mycoplasmasand viruses.
-0.01 μm Pores: Retain all viruses and some large proteins.
Advantages:
Pore size selects organism
Does not alter fluid composition
Good with air
Disadvantages:
Filters are expensive, can be contaminate
Refrigeration:
from 0 to 7oC. Bacteriostatic effect. Reduces metabolic rate of most microbes so they cannot reproduce or produce toxins but psychrophiles still grow.
Freezing: below 0oC.
- Flash Freezing:Does not kill most microbes.
- Slow Freezing: More harmful because ice crystals disrupt cell structure.
- Used for long term food preservation of food, drugs and cultures3-
Lyophilization:
freeze-drying: -195ºC
Very effective and expensive method for long term preservation
Used for biological specimens, food, medication
NB:Over a third of vegetative bacteria may survive 1 year
Most parasites are killed by few days of freezing.
desiccation
In the absence of water, microbes cannot grow or reproduce, but some may remain viable for years. After water becomes available, those start growing again.
Drying or removal of water
Inhibits metabolism
Does not always kill
More effective against bacteria than fungi
Used for food preservation
Susceptibility to desiccation varies widely:
- Neisseriagonnorrhea: Only survives about one hour.
- Mycobacterium tuberculosis: May survive several months.
- Virusesare fairly resistant to desiccation.
- Clostridiumand Bacillus sppMay survive decades.
Three types of radiation kill microbes:
Ionizing Radiation:
Ultraviolet light (Non-ionizing Radiation)
Microwave Radiation:
Ionizing Radiation:
Gamma rays, X rays, electron beams, or higher energy rays. Have short wavelengths (less than 1 nanometer).
Dislodge electrons from atoms and form ions.
Cause mutations in DNA and produce peroxides.
Used to sterilize pharmaceuticals and disposable medical supplies (plastics…)
Used in Food industry
Disadvantages:
Penetrates human tissues. May cause genetic mutations in humans.
Expensive
Ultraviolet light (Non-ionizing Radiation)
Wavelength is longer than 1 nanometer.
Damages DNA by producing mutations.
Used to reduce number of microorganisms in air or clean surfaces: used to disinfect operating rooms, nurseries, cafeterias.
Disadvantages:
Potentially harmful, Damages skin, eyes.
Doesn’t penetrate surfaces: paper, glass, and cloth
Microwave Radiation:
Wavelength ranges from 1 millimeter to 1 meter.
Heat is absorbed by water molecules.
May kill vegetative cells in moist foods.
Bacterial endospores, which do not contain water, are not damaged by microwave radiation.
Solid foods are unevenly penetrated by microwaves.
Trichinosis outbreaks have been associated with pork cooked in microwaves.
Chemical antimicrobial agents should:
- be effective against wide range of microbes
- be effective in presence of organic material
- be toxic to microbe but non-toxic to people and non-corrosive to surfaces
Phenols(carbolic acid) was first used by Lister as a disinfectant.
Rarely used today because it is a skin irritant and has a strong odor.
Used in some throat sprays and lozenge (pastille tablets).
Act as local anesthetic.
Useful to disinfect materials contaminated with organic materials
Denature protein and disrupt cell membranes
b-Phenolicsare chemical derivatives of phenols
Cresols: Derived from coal tar (Lysol).
BiphenolsEffective against gram-positive Staphylococci sppand Streptococci spp.
Some phenolicsare used as antiseptics at low concentrations
Destroy plasma membranes and denature proteins.
Used in nurseries. But excessive use in infants may cause neurological damage.
Especially good at disinfecting in the presence of biological fluids such as pus, saliva
Advantages
Stable, persist for long times after application (long lasting and stable)
Remain active in the presence of organic compounds
iodine
One of the oldest and most effective antiseptics
Effective against all kinds of bacteria, many endospores, various fungi and some viruses
Iodine impairs protein synthesis and alters cell membranes
tincture of iodine
Was one of the first antiseptics used
Denature proteins
Stains skin and clothes, somewhat irritating.
Iodophors: Compounds with iodine that are slowly released
Have the antimicrobial activity of iodine, but they do not stain and are less irritating.
Take several minutes to act.
Used as skin antiseptic in surgery.
Not effective against bacterial endospores.
Ex: Betadine, Isodine
