micro chapter 7

disinfectant

Applied to inanimate objects.

antiseptic

Applied to living tissue

halogens

Effective alone or in compounds. Action: Denature proteins

factors that effect antimicrobial growth

1. Site to be Treated: Will determine the choice of antimicrobials that can be used. 2. Number of Microbes: The more microbes present, the more time it takes to eliminate population. 3. Type of Microbes: Endospores are very difficult to destroy. Vegetative pathogens vary widely in susceptibility to different methods of microbial control. 4 Environmental influences: Presence of organic material (blood, feces, saliva) tends to inhibit antimicrobials, pH etc. 5. Temperature and Time of Exposure: Chemical antimicrobials and radiation treatments are more effective at longer times. In heat treatments, longer exposure compensates for lower temperatures.

Ultrahigh temperature sterilization:

140oC for 1-3 seconds and then cooled very quickly in a vacuum chamber.

sporocide

: An agent that kills bacterial endospores or fungal spores.

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.

membrane filters

: Uniform pore size. Used in industry and research. Different sizes: 0.22 and 0.45um Pores: Used to filter most bacteria. Don't retain spirochetes, mycoplasmas and viruses. 0.01 um Pores: Retain all viruses and some large proteins.

asepsis

Absence of significant contamination

viricide

An agent that inactivates viruses.

Bacteriostatic agent

An agent that inhibits the growth of bacteria, but does not necessarily kill them. Suffix stasis: To stop or steady.

bactericide

An agent that kills bacteria. Most do not kill endospores.

germicide

An agent that kills certain micoorganisms.

fungicide

An agent that kills fungi.

Plasmolysis

As water leaves the cell, plasma membrane shrinks away from cell wall. Cell may not die, but usually stops growing. Yeasts and molds: More resistant to high osmotic pressures. Staphylococci spp. that live on skin are fairly resistant to high osmotic pressure.

gaseous sterilizers

Chemicals that sterilize in a chamber similar to an autoclave. Action: Denature proteins, by replacing functional groups with alkyl groups. A. Ethylene Oxide: Kills all microbes and endospores, but requires exposure of 4 to 18 hours. Toxic and explosive in pure form. Highly penetrating. Most hospitals have ethylene oxide chambers to sterilize mattresses and large equipment.

sepsis

Comes from Greek for decay or putrid. Indicates bacterial contamination.

Pasteurization

Developed by Louis Pasteur to prevent the spoilage of beverages by reducing the number of microbes in milk, wine, juices, beer, etc.

low temperature

Effect depends on microbe and treatment applied.

incineration

Effective way to sterilize disposable items (paper cups, dressings) and biological waste.

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. Action: Cause mutations in DNA and produce peroxides. Used to sterilize pharmaceuticals and disposable medical supplies. The FDA has approved the use of gamma rays for meats, spices, fruits, and vegetables. Kills microbes, insects, and fruit/vegetable cells which prevents both spoilage and overripening. Disadvantages: Penetrates human tissues. May cause genetic mutations in humans and microbes. Concerns about nutritional value of food.

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.

commercial sterilization

Heat treatment that kills endospores of Clostridium botulinum the causative agent of botulism, in canned food. Does not kill endospores of thermophiles, which are not pathogens and may grow at temperatures above 45oC.

chlorine

Hypochlorous acid Used to disinfect drinking water, pools, and sewage. Chlorine is easily inactivated by organic materials. Sodium hypochlorite (NaOCl): Is active ingredient of bleach. Chloramines: Consist of chlorine and ammonia. Less effective as germicides.

Dessication

In the absence of water, microbes cannot grow or reproduce, but some may remain viable for years. After water becomes available, they start growing again. Susceptibility to dessication varies widely: Neisseria gonnorrhea: Only survives about one hour. Mycobacterium tuberculosis: May survive several months. Viruses are fairly resistant to dessication. Clostridium spp. and Bacillus spp.: May survive decades. Lyophilization: Combines freezing and drying with a vacuum, to preserve cells for many years. Use liquid nitrogen or dry ice.

heavy metals

Include copper, selenium, mercury, silver, and zinc. Oligodynamic action: Denature proteins. Very tiny amounts are effective. A. Silver: 1% silver nitrate used to protect infants against gonorrheal eye infections until recently. B. Mercury Organic mercury compounds like merthiolate and mercurochrome are used to disinfect skin wounds. Thimerosol is used in some vaccines (flu), recently removed from most pediatric vaccines.. C. Copper Copper sulfate is used to kill algae in pools and fish tanks. Selenium Kills fungi and their spores. Used for fungal infections. Also used in dandruff shampoos. E. Zinc Zinc chloride is used in mouthwashes. Zinc oxide is used as antifungal agent in paints and diaper rash cream.

Aldehydes:

Include some of the most effective antimicrobials. Action: Denature proteins by forming covalent crosslinks with several functional groups. A. Formaldehyde gas (H2C=O): Excellent disinfectant. Commonly used as formalin, a 37% aqueous solution. Formalin was used extensively to preserve biological specimens and inactivate viruses and bacteria in vaccines. Irritates mucous membranes, strong odor. Also used in mortuaries for embalming. B. Glutaraldehyde: Less irritating and more effective than formaldehyde. One of the few chemical disinfectants that is a sterilizing agent. A 2% solution of glutaraldehyde (Cidex) is: Bactericidal, tuberculocidal, and viricidal in 10 minutes. Sporicidal in 3 to 10 hours. Commonly used to disinfect hospital instruments. Also used in mortuaries for embalming.

alcohols

Kill bacteria, fungi, but not endospores or naked viruses. Action: Denature proteins and disrupt cell membranes. Evaporate, leaving no residue. Used to mechanically wipe microbes off skin before injections or blood drawing. Not good for open wounds, because cause proteins to coagulate. Ethanol: Drinking alcohol. Optimum concentration is 70%. Isopropanol: Rubbing alcohol. Better disinfectant than ethanol. Also cheaper and less volatile.

Sterilization

Killing or removing all forms of microbial life (including endospores) in a material or an object. Heating is the most commonly used method of sterilization.

dry heat

Kills by oxidation effects.

moist heat

Kills microorganisms by coagulating their proteins. In general, moist heat is much more effective than dry heat.

heat

Kills microorganisms by denaturing their enzymes and other proteins and destroying membranes. Heat resistance varies widely among microbes.

thermal death point

Lowest temperature at which all of the microbes in a liquid suspension will be killed in ten minutes.

Degerming

Mechanical removal of most microbes in a limited area. Example: Alcohol swab on skin.

Ultrahigh Temperature Pasteurization (UHT):

Milk is treated at 134oC for 1 second. May affect taste of beverage.

Classic Method of Pasteurization

Milk was exposed to 65oC for 30 minutes.

thermal death time

Minimal length of time in which all bacteria will be killed at a given temperature

Peroxygens (Oxidizing Agents):

Oxidize cellular components of treated microbes. Action: Disrupt membranes and proteins. A. Ozone: Used along with chlorine to disinfect water. Helps neutralize unpleasant tastes and odors. More effective killing agent than chlorine, but less stable and more expensive. Highly reactive form of oxygen. Made by exposing oxygen to electricity or UV light. B Hydrogen Peroxide: uUsed as an antiseptic. uNot good for open wounds because quickly broken down by catalase present in human cells. uEffective in disinfection of inanimate objects. uSporicidal at higher temperatures. uUsed by food industry and to disinfect contact lenses. C. Benzoyl Peroxide: uUsed in acne medications. D. Peracetic Acid: One of the most effective liquid sporicides available. Sterilant : Kills bacteria and fungi in less than 5 minutes. Kills endospores and viruses within 30 minutes. Used widely in disinfection of food and medical instruments because it does not leave toxic residues.

phenols and phenoliles

Phenol (carbolic acid) was first used by Lister as a disinfectant. Rarely used today because it is a skin irritant and has strong odor. Used in some throat sprays and lozenges. Acts as local anesthetic. Phenolics are chemical derivatives of phenol Cresols: Derived from coal tar (Lysol). Biphenols (pHisoHex): Effective against gram-positive staphylococci and streptococci. Used in nurseries. Excessive use in infants may cause neurological damage. Action: Destroy plasma membranes and denature proteins. Advantages: Stable, persist for long times after applied, and remain active in the presence of organic compounds.

hot air sterilization

Place objects in an oven. Require 2 hours at 170oC for sterilization. Dry heat is transfers heat less effectively to a cool body, than moist heat.

Disinfection

Reducing the number of pathogenic microorganisms to the point where they no longer cause diseases. Usually involves the removal of vegetative or non-endospore forming pathogens.

moist heat continued

Reliable sterilization with moist heat requires temperatures above that of boiling water. 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.

freezing

Temperatures below 0oC. Flash Freezing: Does not kill most microbes. Slow Freezing: More harmful because ice crystals disrupt cell structure. Over a third of vegetative bacteria may survive 1 year. Most parasites are killed by a few days of freezing.

refrigeration

Temperatures from 0 to 7oC. Bacteriostatic effect. Reduces metabolic rate of most microbes so they cannot reproduce or produce toxins.

osmotic pressure

The use of high concentrations of salts and sugars in foods is used to increase the osmotic pressure and create a hypertonic environment.

decimal reduction time

Time in minutes at which 90% of bacteria at a given temperature will be killed. Used in canning industry.

iodine

Tincture of iodine (alcohol solution) was one of first antiseptics used. Combines with amino acid tyrosine in proteins and denatures proteins. Stains skin and clothes, somewhat irritating. Iodophors: Compounds with iodine that are slow releasing, take several minutes to act. Used as skin antiseptic in surgery. Not effective against bacterial endospores. Betadine Isodine

Sanitization

Use of chemical agent on food-handling equipment to meet public health standards and minimize chances of disease transmission. E.g: Hot soap & water.

High Efficiency Particulate Air Filters (HEPA):

Used in operating rooms and burn units to remove bacteria from air.

direct flaming

Used to sterilize inoculating loops and needles. Heat metal until it has a red glow.

Flash (High Temperature Short Time) Pasteurization:

Used today. Milk is exposed to 72oC for 15 seconds.

Ultraviolet light (Nonionizing Radiation):

Wavelength is longer than 1 nanometer. Action: Damages DNA by producing thymine dimers, which cause mutations. Inhibits DNA transcription and replication, Used to disinfect operating rooms, nurseries, cafeterias. Disadvantages: Damages skin, eyes. Doesn't penetrate 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.

Quaternary Ammonium Compounds (Quats):

Widely used surface active agents. Cationic (positively charge) detergents. Effective against gram positive bacteria, less effective against gram-negative bacteria. Also destroy fungi, amoebas, and enveloped viruses. Zephiran, Cepacol, also found in our lab spray bottles. Pseudomonas strains that are resistant and can grow in presence of Quats are a big concern in hospitals. Advantages: Strong antimicrobial action, colorless, odorless, tasteless, stable, and nontoxic. Diasadvantages: Form foam. Organic matter interferes with effectiveness. Neutralized by soaps and anionic detergents.

aseptic technique

are used to prevent contamination of surgical instruments, medical personnel, and the patient during surgery. Aseptic techniques are also used to prevent bacterial contamination in food industry.