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Control of Microbial Growth
Terms in this set (82)
Removing or destroying all microorganisms and viruses on or in a product
eliminates most or all pathogens in or in material
Disinfectants used on inanimate objects
Antiseptics used on living tissues (skin)
brief heating to reduce number of spoilage organisms, destroy pathogens
Foods, inanimate objects
reduce pathogens to levels considered safe to handle
substantially reduced microbial population that meets accepted health standards. Not a specific level of control
process of delaying spoilage of foods and other perishable products. Adjust storage conditions. Add bacteriostatic (growth-inhibiting) preservatives
Minimizing microbial population very important
Danger of healthcare-associated infections
Patients more susceptible to infection
May undergo invasive procedures (e.g., surgery)
Pathogens more likely found in hospital setting
Feces, urine, respiratory droplets, bodily secretions
Instruments must be sterilized to avoid introducing infection to deep tissues
Prions relatively new concern; difficult to destroy
Routinely work with microbial cultures and use rigorous methods of control. Used to prevent contamination of samples, self, laboratory. CDC guidelines for labs working with microbes
Biosafety levels range from BSL-1 (microbes not known to cause disease) to BSL-4 (lethal pathogens for which no vaccine or treatment exists).
Water Treatment Facilities
Chlorine traditionally used to disinfect water
Some organisms resistant to chemical disinfectants
Cryptosporidium parvum (causes diarrhea)
Food and Food Production Facilities
Perishables retain quality longer when contaminating microbes destroyed, removed, inhibited. Heat treatment most common and reliable mechanism can alter flavor, appearance of products. (ideal method does not exist).
Type of Microorganism
Multiple highly resistant microbes
Only extreme heat or chemical treatment ensures their complete destruction. May require 10 hours to destroy. (ex. Bacillus and Clostridium)
Protozoan cysts and oocysts
resistant to disinfectants; excreted in feces; causes diarrheal disease if ingested. Particular concern in water treatment. They are readily destroyed by boiling. (ex. Giardia lamblia and Cryptosporidium parvum).
waxy cell walls makes resistant to many chemical treatments. Toxic disinfectants must be used. (Ex. Mycobacterium tuberculosis).
resistant to some chemical disinfectants but some can actually grow in them.
Viruses such as poliovirus that lack a lipid envelope; more resistant to disinfectants. (HIV tends to be sensitive to heat and chemical disinfectants).
Number of Microorganisms
Time for heat, chemicals to kill affected by population size
Fraction of population dies during given time interval
Large population = more time. Removing organisms by washing reduces time
Decimal reduction time
(D value) gauges commercial effectiveness. Time required to kill 90% of population under specific conditions
is one of the most useful methods of microbial control. Reliable, safe, relatively fast, inexpensive, non-toxic
Can be used to sterilize or disinfect
Methods include moist heat, dry heat
destroys microorganisms by irreversibly coagulating their proteins. They include boiling, pasteurization and pressurized steam.
destroys most microorganisms and viruses
Does not sterilize: endospores can survive
destroys pathogens, spoilage organisms
(HTST) method is used. Milk is heated to 72 C and held for 15 seconds. Ice cream is heated to 82 C for 20 seconds.
(UHT) method is used. Milk is heated to 140°C to 150 C for a few seconds, then rapidly cooled. Aseptically packaged and treated with germicide hydrogen peroxide. Shelf-stable boxed juices and milk are processed and packaged in a similar manner ("ultra Pasteurization").
used to sterilize using pressurized steam
Increased pressure raises temperature; kills endospores
Sterilization typically at 121°C and 15psi in 15 minutes
Longer for larger volumes.
sterilization at higher temperature can be used.
Prions thought destroyed at 132°C for 1 hour
Commercially canning process uses pressurized steam in an industrialized-size autoclave. Designed to destroy Clostridium botulinum endospores. Critical because surviving endospores can germinate in canned foods; cells can grow in low-acid anaerobic conditions and produce Botulinum toxin.
Canned food; Endospores of some thermophiles may survive.
Less effective than moist heat; longer times, higher temperatures necessary.
-200°C for 90 minutes vs. 121°C for 15 minutes
Hot air ovens oxidize cell components, denature proteins
Incineration a method of dry heat sterilization, oxidizes cell to ashes. Laboratory inoculation loop sterilized by flaming
retains bacteria while allowing fluid to pass through.
have microscopic pores that allow liquid to flow through. The pore size is 0.2 micrometers (um) are commonly used to remove bacteria.
trap material within thick filtration material such as cellulose fibers or diatomaceous earth. Thick porous filtration material (e.g., cellulose) Larger pores, electrical charges trap cells
Filtration of air
High-efficiency particulate air (HEPA) filters remove nearly all microbes from air
They include, radio waves, microwaves, visible and ultraviolet light, X-rays, and gamma rays. This energy travels by waves and has no mass.
inversely proportional to frequency
is the number of waves per second. Short waves have high frequency while long waves have low frequency.
can remove electrons from atoms
Destroys DNA and damages cytoplasmic membranes
Reacts with O2 to produce reactive oxygen species
Gamma rays and X-rays important forms
Used to sterilize heat-sensitive materials
Approved for use on foods, although consumer resistance has limited use
FDA has approved for fruits, vegetables, and grains (for insect control), pork (for parasite control), and poultry, beef, lamb, and pork (for bacterial control)
destroys microbes directly
Damages DNA and destroys microbes in air, water, and on surfaces. Poor penetrating power. Thin films or coverings can limit effect. Cannot kill microbes in solids or turbid liquids
Most glass and plastic block. Must be carefully used since damaging to skin, eyes
kill by generated heat, not directly. Microwave ovens heat food unevenly, so cells can survive
Used in pasteurization of commercial foods E.g., guacamole
Avoids problems with high temperature pasteurization
Employs high pressure up to 130,000 psi.
Destroys microbes by denaturing proteins and altering cell permeability. Products maintain color, flavor associated with fresh food
Can destroy all microorganisms, including endospores and viruses. Sterilants used to treat heat-sensitive critical instruments such as scalpels.
destroy viruses, vegetative cells. Do not reliably kill endospores
Used to treat semicritical instruments such as gastrointestinal endoscopes.
destroy vegetative bacteria, mycobacteria, fungi, and most viruses, but not all. Used to disinfect non-critical instruments such as stethoscopes.
destroy fungi, vegetative bacteria but not mycobacteria and enveloped viruses, nor endospores and naked viruses. Used to disinfect furniture, floors and wall.
Germicides are at least somewhat toxic to humans and the environment. The benefit of disinfecting or sterilizing an item must be weighed against the risk associated with using the germicide procedure.
Many germicide chemical such as hypochlorite are readily inactivated by organic matter and are not appropriate to use in situations where organic material is present.
Electrical equipment cannot tolerate liquid chemical germicides, and so gaseous alternatives must be employed.
Many chemical residues lease a residue that is toxic or corrosive. To remove residue you need to wash down with sterile water.
Cost and availability
Some germicides are less expensive and more readily available than others.
Storage and stability
Some germicides are available in concentrated stock solutions, decreasing the required storage space.
can interfere with sewage treatments system that utilize microorganisms to degrade sewage. These germicides must be neutralized before disposal.
60-80% aqueous solutions of ethyl or isopropyl alcohol
Kills vegetative bacteria and fungi. Not reliable against endospores, some naked viruses. Coagulates essential proteins and enzymes by damaging lipid membranes.
More soluble in water; pure alcohol less effective. Commonly used as antiseptic and disinfectant.
Evaporates quickly, limiting contact time
Can damage rubber, some plastics, and others
Used to degerm skin in preparation for procedures that break intact skin, and as disinfectants for treating instruments.
(aldehydes) Glutaraldehyde, formaldehyde, and orthophthalaldehyde destroy microorganisms and viruses by inactivating proteins and nucleic acid. Immersion for 10-12 hours kills all microbial life. Formaldehyde used as gas or as formalin (37% solution) that kills most forms of microbial life.
2% alkaline glutaraldehyde common sterilant for treating heat-sensitive medical items. Effective germicide that kills most microbes quickly used to kill bacteria and inactivate viruses for vaccines. Used to preserve specimens.
Chlorhexidine most effective of this group. Extensive in antisepticsStays on skin, mucous membranes
Relatively low toxicity, destroys vegetative bacteria, fungi, some enveloped viruses. Common in many products: skin cream, mouthwash.
Chlorhexidine is widely used as an antiseptic in soaps and lotions, impregnated into catheters and surgical mesh.
Extremely useful gaseous sterilizing agent that destroys all microbes, including endospores and viruses, by reacting with proteins. Penetrates fabrics, equipment, implantable devices
Pacemakers, artificial hips. Applied in special chamber resembling autoclave. Limitations: mutagenic and potentially carcinogenic
Ethylene oxide Uses
Useful in sterilizing heat or moisture sensitive items such as electrical equipment; medical devices, pillows, and mattresses. Disposable laboratory items, including plastic Petri-dish and pipets are also sterilized with ethylene oxide.
Chlorine and iodine are common disinfectants that are thought to act by oxidizing proteins and other essential cell components.
Destroys all types of microorganisms and viruses but is too irritating to skin and mucous membranes to be used as an antiseptic. 1:100 dilution of household bleach effective. Cryptosporidium oocysts, Giardia cysts survive
Presence of organic compounds a problem
Chlorine dioxide used as disinfectant and sterilant.
Very low levels disinfect drinking water and waste water, objects, surfaces.
Unlike chlorine, does not reliably kill endospores, but it can be used as a disinfectant. Can be used as iodophore, in which the iodine is linked to a carrier molecule that releases free (unbound) iodine slowly.
Not irritating to skin as tincture iodine nor they stain. Tincture or iodine and iodophore can be sued as disinfectants or antiseptics.Some Pseudomonas species can survive in stock solution
kill microorganisms by combing with sulfhydryl groups of enzymes and other proteins. High concentrations too toxic to be used medically
Metal Compounds Uses
Silver still used as disinfectant: creams, bandages.
Silver nitrate used for eye drops which were required to prevent Neisseria gonorrhoeae infections acquired during birth
Antibiotics have largely replaced silver nitrate.
Compounds of mercury, tin, copper, and others once widely used as preservatives, in industrial products
To prevent microbial growth in recirculating cooling water
Extensive use led to environmental pollution which is now strictly regulated
O3 is an unstable form of oxygen that is a powerful oxidizing agent. Decomposes quickly, so generate on site.
Used as alternative to chlorine
Disinfectant for drinking and wastewater
powerful oxidizers and peracetic acid are used as sterilants. Readily biodegradable, no residue
Less toxic than ethylene oxide, glutaraldehyde
H2O2 effectiveness as a germicide depends in part on whether it is used on living tissue, such as a wound, or inanimate object.
Hydrogen Peroxide Uses
Aerobic cells (body tissues) produce enzyme catalase that
breaks down H2O2 to O2, H2O which breaks it down quickly. More effective on inanimate object. Doesn't damage most materials. Hot solutions used in food industry (packed juices)
Vapor-phase can be used as sterilant.
More potent germicide than hydrogen peroxide H2O2. Both peroxygens can be used to sterilize in less than an hour. Effective in organic compounds leave no residue. Sharp odor and it is irritating to skin and eyes.
Peracetic acid Uses
is widely used to disinfect and sterilize medical devices.
Phenolic Compounds (Phenolics)
Phenol one of earliest disinfectants, but limited because of an unpleasant odor and irritates skin. kill most vegetative bacteria
Mycobacterium at high concentrations. Not reliable on all virus groups. Destroy cytoplasmic membranes and denature proteins. Wide activity range, reasonable cost, remain effective in presence of detergents and organic contaminants
Leave antimicrobial residue
Phenolic Compounds (Phenolics) Uses
Some non-toxic, Triclosan used in personal products including toothpaste, lotions, soaps. Hexachlorophene effective against Staphylococcus Aureus, used limited because it can cause neurological damaged.
Quaternary Ammonium Compounds
also called quats, are cationic (positive charged) detergents that are non-toxic enough to be used to disinfect food preparations surfaces. Have both charged hydrophilic and uncharged hydrophobic regions.Reduces surface tension of liquids. Aids in removal of dirt, organic matter, organisms.
But positive charge of Quats attracts them to negative charge of cell surface. Reacts with membrane. Destroys vegetative bacteria and enveloped viruses. Not effective on endospores, mycobacteria, naked viruses. Pseudomonas resists, can grow in solutions.
Quaternary Ammonium Compounds Uses
Most household soaps, detergents are anionic. Used to disinfect inanimate objects and to preserve non-food substances.
Weak organic acids
benzoic, sorbic, propionic; sometimes added to foods such as bread, cheese, and juice to prevent microbial growth. Low PH acids alter cell membrane and interfere with energy transformation. Added to acidic foods to prevent fungi growth, mold and bacteria cosmetic products.
Nitrate and nitrite
Used in processes meats. Inhibit endospore germination and vegetative cell growth. Stops growth of Clostridium botulinum. Higher concentrations give meats pink color.
Reducing Available Water
salting, sugar or drying food have been used to preserve food. Decreases availability of water in food below limits required for most microbial growth. High-solute causes plasmolysis, which damages microbial cells.
Refrigeration inhibits growth of pathogens and spoilage organisms by slowing or stopping enzyme reactions
Psychrotrophs, psychrophilic organisms can still grow
Freezing preserves by stopping all microbial growth
stops microbial growth but does not reliably kill fungi in or in foods.
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