chapters 5.1-5.5

Term Definition
Sterilization removal of all microorganisms. Sterile item is free of microbes including endospores and viruses. (but does not consider prions)
Disinfection Elimination of most or all pathogens. Some viable microbes may remain. Disinfectants used in inanimate objects. may be called biocides, germicides, bactericides.
Antiseptics used on living tissues
Pasteurization belief heating to reduce number of spoilage organisms and destroy pathogens. Foods, Inanimate objects.
Decontamination reduce pathogens to levels considered safe to handle.
Sanitized substantially reduced microbial population that meets accepted health standards. Not specific level of control
Preservation process of delaying spoilage of foods and other perishable products.
-adjust conditions
-add bacteriostatic ( growth inhibiting) preservatives
Situational Considerations microbial control methods depend upon situation and level of control required
Daily life
(approaches to control)
washing and scrubbing with soaps and detergents achieves routine control.
-soap aids in mechanical removal of organism
-beneficial skin microbiota reside deeper on underlying layers of skin, hair follicles
– not adversely affected by regular use
Hospitals minimizing microbial pop. very important.
danger of healthcare associated infections. Pts more susceptible to infections. May undergo invasive procedures. Pathogens more likely found in bodily secretions. Prions relatively new concern. hard to destroy
Microbiology Labs Routinely work with microbial cultures. Use rigorous methods of control. must eliminate microbial contamination to both experiment and environment. treatment both before and after. aseptic techniques used to prevent contamination of samples, self, lab
CDC guidelines for 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)
Food and Food Production Facilities Perishables last longer when contamination microbes destroyed, removed. Heat treatments is the most common. Can alter flavor & appearance. Irradiation appeared to treat certain food. Chemical additives can prevent spoilage. FDA regulates. Facility clean.
Water Treatment Facilities Ensure drinking water free of pathogens. Chlorine traditionally used to disinfect. can react to naturally occurring chemicals. form disinfection by products. Some DBP's linked to long term health risks. regulations require facility to minimize DBP.
Organism resistant to chemical infections Cryptosporidium Parvum (causes diarrhea)
Required to be treated
Selection of effective procedure is complicated.. Ideal method does not exist
each has drawbacks and procedural parameters
Choice depends on numerous factors Type and number of microbes
Environmental Conditions
Risk of infection
Composition of infected item
Bacterial Endospores most resistant, only extreme heat or chemical treatment destroys them
Protozoan Cysts and Oocysts resistant to disinfectants, excreted in feces, causes diarrhea disease if ingested
Mycobacterium species waxy cell walls make resistant to many chemical treatments
Pseudomonas species resistant to and can actually grow in some disinfectants
Non-enveloped viruses lack lipid envelope; more resistant to disinfection's
Number of Microorganisms Time for heat, chemicals to kill affected population size
Fraction of population dies during given time interval Large populations= more time
removing organism by washing reduces time
Decimal Reduction time (D value) gauges commercial effectiveness
Time required to kill 90% of population under specific conditions
Environmental conditions Dirt, grease, body fluids can interfere with heat penetration action of chemicals. Microorganisms in biofilm are most resistant. Ph temp, can influence effectiveness. Sodium hypochlorite. Even more effective at low pH.
Critical items. Come in contact with body tissue.
Must be sterile
Include needles and scalpels.
Semi critical items Contact mucous membrane but do not penetrate body tissu . Must be free of viruses and vegetative bacteria. Few endospores blocked by mucous membranes. Include endoscope and endotracheal tubes
Noncritical instruments Contact unbroken skin only.
Low risk of transmission
Countertops, stethoscopes, blood pressure cuffs
Composition of Item Some sterilization and disinfection methods inappropriate for certain items. heat inappropriate for plastics and other sensitive items. irradiation provides alternative, but damages some types of plastics. moist heat, liquid chemicals not be used.
Heat treatment used for microbial control reliable, safe, relatively fast, non toxic. can be used to sterilize or disinfect. methods include moist heat, dry heat
Moist heat irreversibly denatures proteins.
Boiling destroys most microorganisms and viruses. does not sterilize, edospores can survive
Pasteurization destroys pathogen, spoilage organism. high temp-short time: most products. Milk 72*c for 15s Ice cream 82*c for 20s
Ultra high temp Shelf stable boxed juice and milk known as Ultra-pasteurization
milk 140*c for a few seconds then rapidly cooled
Autoclave used to sterilize using pressurized steam. increased pressure raises temp. kills endospores. sterilization usually 121*c 15psi 15min, longer for large volume, flash sterilization at higher temp can be used. Prions thought destroyed 132*c 1hr
Commercial Canning process Uses industrial autoclave called retort. Designed to destroy Clostridium botulinum endospores. virtually impossible to have so many endospores. critical because otherwise endospores can germinate in canned food
how is botulinum toxin produced cells grow in low-acid anaerobic conditions, and produce it.
canned food commercially sterile endospores of some thermophiles may survive. usually not a concern. only grow at temperature well about normal storage.
Dry heat less effective than moist heat. longer times, higher temperature necessary. 200*c for 90 mins. vs 121*c for 15mins. Hot air ovens oxidize cell components, denature proteins.
Incineration a method of dry heat Oxidized cell to ashes. Used to destroy medical wast and animal carcasses. Lab inoculation, loop sterilized by flame
Filtration retains bacteria some material cannot withstand heat treatment. Filtration of fluids used extensively
Membrane filters small pore size (0.2)
Depth Filters thick porous filtration material.
larger pores
electrical charge in trap cells
Filtration of air high-efficiency particulate air (HEPA) filters removes nearly all microbes from air
Electromagnetic Radiation radio waves, microwaves, visible and ultraviolet light, x rays, gamma ray. Energy travels in waves; no mass. Wavelength inversely proportional to frequency. High frequency has more energy than low
Ionizing Radiation Gamma rays and x rays are important. Destroys DNA. Damages cytoplasmic membrane. Reacts with O2 to produce reactive oxygen species
High energy Gamma rays Used to sterilize heat sensitive materials. Generally used after packaging. Approved for the use on food. although consumer resistance has limited use
What has the FDA approved ? approved for species and dried herbs, fruits , vegetables, and grains (insect control) pork (parasite control) poultry, beef, lamb, and pork (bacterial control)
Ultraviolet Radiation destroys microbes directly. Damages DNA. Used to destroy microbes in air, water, and surfaces.
Poor penetrating Power thin films or coverings can limit effect. Cannot kill microbes in solid or turbid liquids. Most glass and plastic blocks. Must be carefully used, can damage skin, eyes
Microwaves kill by generated heat. Not directly. Microwave ovens heat food unevenly, so cells can survive.
High Pressure used in pasteurization of commercial food. avoids problems with high temp pasteurization. Employs high pressure 130,000psi destroys microbes by denaturing protein and altering cell permeability. maintain color & flavor
Sterilants destroy all microorganisms. Heat sensitive critical instruments
High level disinfectants destroy viruses, vegetative cells. Do not reliably kill endospores. Semi critical Instruments
Intermediate level disinfectants destroy vegetative bacteria, mycobacteria, fungi, and most viruses. Disinfect non critical instruments
Low level disinfectants destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses. Do not kill endospores, naked viruses. Disinfects furniture, floors, walls
Toxicity Benefits must be weighed against risk of use
Activity In presence of organic material. Many germicides inactivated
Compatibility with material being treated. Liquids; cannot be used on electrical equipment
Residues can be toxic or corrosive
Cost and availability
Storage and stability Concentrated stock decreases storage space
Environmental Risks agent may need to be neutralized before disposal.
Alcohols 60-80% aqueous solutions of ethyl or isopropyl alcohol . Not vegetative bacteria and fungi. Not reliable against endospores, some naked viruses. Damage to lipid membranes. Commonly used as antiseptic and disinfectants.
Alcohols. (coagulates essential proteins Enzymes. More soluble in water, pure alcohol less effective
Alcohol (limitations) evaporates quickly, limiting contact time. Can damage rubber, some plastics, and others.
Aldehydes Glutaraldehyde, formaldehyde, orthophthalaldehyde. inactivates proteins and nucleic acids. 2% alkaline glutaraldehyde, common sterilant. immersion for 10-12hrs. kills all microbial life. Toxic
Formaldehyde used as a gas or as formalin (37% solution). Effective germicide that kills most microbes quickly. Used to kill bacteria and inactivate viruses for vaccines. Used to preserve specimen.
Biguanides Chlorhexidine most effective. Extensive in antiseptics. Stays on skin, mucous membranes. Relatively low toxicity. Destroys vegetative bacteria, fungi, enveloped viruses, common in many products skin cream. mouthwash
Ethylene Oxide useful gaseous sterilant. Destroys microbes including endospores and viruses. Reacts with proteins. Penetrates fabrics, equipment, implantable, devices. Pacemakers, artificial hips. Useful in sterilizing heat or moisture sensitive items.
Ethylene Oxide continued.. Many disposable laboratory items. Petri dishes, pipettes. Applied in special chamber resembling autoclave. Limitations, toxic, (must be extensively aired) mutageni and potentially carcinogenic
Halogens oxidized proteins, cellular components
Chlorine destroys all microorganisms and viruses. used as disinfectant. caustic to skin and mucous membranes. 1:100 dilution of household bleach effective. very low levels disinfects drinking water. Cryptosporidium oocyst, Giardia cysts survive.
Chlorine continue. Presences of organic compounds a problem. Chlorine dioxide used as disinfectant and sterilant
Iodine Kills vegetative cells, unreliable on endospores. Commonly used as Iodophore. Iodine slowly released from carrier molecule. Some pseudomonas species can survive in stock solutions.
Metal Compounds combine with Sulfhydryl groups of enzymes, proteins. High Concentration too toxic to be used medically. Silver still used as disinfectant. creams, bandages. Antibiotics have largely replaced
Example of metal compounds Silver nitrate eye drops were required to prevent Neisseria Gonorrhoeae infections acquired during birth.
Compounds of mercury, tin, copper widely used as preservatives in industrial products. To prevent microbial growth in recirculating cooling water. Extensive use led to environmental pollution. Now strictly regulated.
Ozone O3 unstable form of oxygen. Decomposes quickly so generated on site. Powerful oxidizing agent. used as alternative to chlorine. Disinfectant for drinking and wastewater.
Peroxygens powerful oxidizers used as sterilants. Readily biodegradable, no residue. Less toxic than ethylene oxide, glutaraldehyde
Hydrogen peroxide Effectiveness depends on surface. aerobic cells produce enzyme catalase. Breaks down H2O2 to O2 H2O. More effective on inanimate objects. Doesnt damage most materials. hot solutions. Vapor phase can be used as sterilant
Peracetic acid most potent than H2O2 effective on organic material. Useful on wide range of material.
Phenolic Compounds. Phenol one of earliest disinfectants. Has unpleasant odor. irritates skin. Phenolics kill most vegetative bacteria. Mycobacterium at high concentrations. Not reliable on all virus groups. Cautioned by FDA; Triclosan, hexachlorophene
Phenolic Compounds continued Destroy cytoplasmic membranes, denature proteins. Wide activity range, reasonable cost, remain effective in presence of detergents and organic contaminants. Leave antimicrobial residue. Consider non toxic for skin applications use caution by FDA.
Catonic Positively charged. detergents. nontoxic used to disinfect food preparation surfaces. Charged hydrophilic and uncharged hydrophobic regions. reduces surface tension in lipids. Aids in removal of dirt
Quaternary Ammonium compounds continued Most household soaps detergents are anionic. but positive charge of quats attracts them to negative charge of cell surface. Reacts with membrane. Destroys vegetative bacteria and enveloped viruses. no effective on endospores. Pseudomonas resists,

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