Lec08 Ch11 Disinfection and decon PDF

Chemical and Physical control Ways to kill microbes Controlling microorganisms Historical microbial control methods: – Salting food – Smoking food – Pickling food – Drying food – Exposing food, clothing, and bedding to sunlight General considerati...

Chemical and Physical control Ways to kill microbes Controlling microorganisms Historical microbial control methods: – Salting food – Smoking food – Pickling food – Drying food – Exposing food, clothing, and bedding to sunlight General considerations in microbial control Three outcomes of microbial control outside the body – Sterilization – destroy all microbial life Autoclave, radiation, ethylene oxide gas, vaporized hydrogen peroxide, vaporized formaldehyde – Disinfection – destroy most microbial life on inanimate surfaces Bleach, UV light – Antisepsis – destroy most microbial life on animate surfaces Hand washing, iodine Decontamination/Sanitation – Mechanical removal from any surface – Includes disinfection and antisepsis General considerations in microbial control Sterilization – Requires specialized equipment i.e. autoclave – Sterilized items contaminated upon environmental exposure – Sterile technique an effort to maintain sterility Disinfection – Uses more readily available means Bleach, boiling – Helpful in daily life, but does not kill everything Surfaces are not 100% safe Microbial control methods overview  Relative resistance of microbial forms Primary targets of microbial control: – Microorganisms capable of causing infection or spoilage Usually mesophilic bacteria adapted to live at environmental and/or body temperature Can be organisms not dangerous by themselves, but that produce a toxin – Constantly present in the external environment and on Clostridium botulinum the human body – Most of these bacteria are not harmful – Some microorganisms are more resistant to disinfectants than others  Relative resistance of microbial forms Bacterial endospores: – Destruction of endospores is the goal of sterilization – Any process that will kill endospores will invariably kill less resistant microbial forms – Other methods of control (disinfection, antisepsis) act on microbes that are less hardy than endospores  Relative resistance of microbial forms Bacterial endospores: – Destruction of endospores is the goal of sterilization – Any process that will kill endospores will invariably kill less resistant microbial forms – Other methods of control (disinfection, antisepsis) act on microbes that are less hardy than endospores Antimicrobial agents Germicide and microbicide: chemical agents that kill microorganisms – Bactericide: A chemical that destroys bacteria except for those in the endospore stage – Fungicide: kills fungal spores, hyphae, and yeasts – Virucide: inactivates viruses, especially on living tissue – Sporicide: capable of killing endospores Antimicrobial agents Bacteriostatic agents Prevent growth of bacteria on tissues of objects -stasis = to stand still Do not kill organisms, only stop growth Fungistatic agents – Inhibits fungal growth Microbiostatic agents – Control microbes in the body Drugs and antiseptics Decontamination Sanitization – Any cleansing technique that mechanically removes microbes and debris – Reduces contamination to safe levels – Sanitizer: soap, detergent, or other chemical used to sanitize Decontamination Antisepsis – Reduction of the number of microbes on the skin – Involves scrubbing the skin or immersing it in chemicals, or both – Emulsifies oils on the outer cutaneous layer – Mechanically removes potential pathogens on the outer layers of the skin Practical Concerns in Microbial Control Does the item in question require sterilization, or is disinfection adequate? Is the item to be reused or permanently discarded? If it will be reused, can the item withstand heat, pressure, radiation, or chemicals? Is the control method suitable for a given application? Will the agent penetrate to the necessary extent? Is the method cost- and labor-efficient, and is it safe? Practical Concerns in Microbial Control Critical medical devices: – Expected to come into contact with sterile tissues Semi-critical medical devices: – Come into contact with mucosal membranes Noncritical medical devices: – Those that do not touch the patient or are only expected to touch intact skin Bedding, towels Microbial death – What is it? – Hard to detect – Lethal agents do not alter the overt appearance of microbial cells – Loss of movement cannot be used to indicate death Factors that affect death rate Number of microorganisms – Microbicidal agents are used up as they kill Nature of the microbes in the population – What resistance factors are present? – Antibiotic resistance, chemical resistance, capsule… Type of microbial growth – Exponential vs. stationary phase Temperature and pH of the environment Concentration of the agent Mode of action of the agent Presence of solvents, interfering organic matter, and inhibitors Contact time Factors that affect death rate How antimicrobial agents work Cellular targets of physical and chemical agents – Cell wall – Cell membrane – Proteins – Cellular synthetic processes DNA, RNA and protein synthesis Effects of agents on the cell wall Damage to the cell wall: – Blocking cell wall synthesis – Digesting the cell wall – Breaking down the surface of the cell wall A cell with a damaged cell wall is fragile and becomes lysed easily. – Alcohols and some antibiotics disrupt the cell wall – Alcohols perform same function on cell walls as plasma membranes Antibiotics usually inhibit synthesis of new cell walls Effects of agents on the cell membrane The cell membrane and viral envelope are composed of lipids and proteins. Disruption of the cell membrane causes: – Loss of selective permeability – Loss of vital molecules – Allows the entry of damaging chemicals Can be disrupted with alcohols and detergents Effects of agents on protein and nucleic acid synthesis Microbial cells depend on an orderly and continuous supply of proteins. – Substances that inhibit ribosomes will also inhibit protein synthesis Nucleic acids are necessary for the continued functioning of microbes – Agent that impedes the transcription of DNA replication or DNA transcription or changes the genetic code is antimicrobial Agents that alter protein function Native state: – The normal three-dimensional configuration of a protein that allows proper function Denature: – Disruption of proteins, rendering them nonfunctional – Breaking of the bonds that maintain the secondary and tertiary structure – pH, heat, solvents, redox reagents, etc. – Method is non-specific Metallic ions can also bind active sites to block substrate binding Heat as an agent of microbial control Moist heat: – Hot water, boiling water, steam – Temperature ranges from 60°C to 135°C – Operates at lower temperatures and shorter exposure times than dry heat – Most microbicidal effect is coagulation and denaturation of proteins to permanently halt microbial metabolism Heat as an agent of microbial control Autoclaving - wet heat under pressure to sterilize – Requires temperatures above boiling to kill spores – But boiling in open vessels will damage media/reagents – Boil in a pressure vessel Higher temperatures Liquids don’t boil Heat as an agent of microbial control Other methods of disinfection – Pasteurization Used for beverages 71.6°C for 15 seconds 63-66°C for 30 minutes – Tyndallization Media with heat sensitive components Expose to steam intermittently, and not under pressure Heat as an agent of microbial control Dry heat: – Air with a low moisture content that has been heated by a flame or electric heating coil – Temperature ranges from 160°C to several thousand degrees Celsius – Lack of water increases stability of some protein configurations, necessitating higher temperatures – At high temperatures, dry heat oxidizes cells, burning them to ashes Relative effectiveness of various temperatures Both temperature and length of exposure should be considered for adequate sterilization. – Higher temperatures allow shorter exposure times – Lower temperatures require longer exposure times Standard is to kill Geobacillus stearothermophilus spores Why is this organism used? The effects of cold and desiccation Cold treatment retards activities of microbes Desiccation can kill some pathogens, but not all Lyophilization (freeze and dry) is used to preserve some microbes Some pathogens can still grow at refrigeration temperatures – Listeria monocytogenes Radiation as a microbial control agent Radiation: – Energy emitted from atomic activities and dispersed at high velocity through matter or space Radiation suitable for microbial control: – Gamma rays-most effective; most common method for medical sterilization – X-rays – Ultraviolet radiation The effects of radiation Gamma and X-rays – ionizing radiation – Very high energy – Remove electrons from atoms and molecules UV light – nonionizing – High energy – Causes adjacent thymine residues in DNA to crosslink – Leads to mutations upon DNA replication – Prevents RNA synthesis Can’t make proteins Cells eventually die Applications of Filtration Used in liquids that cannot withstand heat. Alternative method for decontaminating milk and beer. Important step in water purification. Efficient means of removing airborne contaminants. – HEPA filters in vacuums, airplanes, respirators Osmotic pressure as a growth suppressant Adding large amounts of salt or sugar to foods creates a hypertonic environment. – Causes plasmolysis (membrane disruption) in bacteria – Makes it impossible for microbes to multiply – “Cured” meats can be kept for long periods without refrigeration – High sugar in jams and jellies has the same effect Selecting a microbicidal chemical Desirable qualities of a germicide: – Rapid action in low concentrations – Solubility in water or alcohol and long-term stability – Broad-spectrum microbicidal action without toxicity to human and animal tissues – Penetration of inanimate surfaces to sustain a cumulative or persistent action – Resistance to becoming inactivated by organic matter – Noncorrosive or non-staining properties – Sanitizing and deodorizing properties – Affordability and ready availability Not always possible to meet all these characteristics – Especially broad-spectrum effectiveness, while at the same time not being toxic to non-target organisms – Bleach is very effective, but toxic to all living organisms – Antibiotics/antivirals are safe to non-target organisms, but often target a specific type of organism