MICRO: ch. 11 study guide
Name four categories of cellular targets for physical and chemical agents.
*[1.]* cell wall >> blocking cell wall synthesis >> digesting cell wall >> breaking down the surface of cell wall *[2.]* cytoplasmic membrane - lipids & proteins {+} (or) viral envelope >> loss of selective permeability >> loss of vital molecules >> allows entry of damaging chemicals *[3.]* cellular synthetic processes [•] DNA [•] RNA [•] protein synthesis *[4.]* proteins
Discuss several different halogen antimicrobial agents and their uses in microbial control
*—HALOGENS—* >> chlorine {+} sodium hypochlorite == bleach {+} chloramines >> iodine {+} free iodine {+} iodophors [•] Betadine [•] Povidone [•] Isodine >> fluorine >> bromine >> *Microbicidal and sporicidal* >> Active ingredients in 1⁄3 of all antimicrobial chemicals
Phenol
1st adopted by Joseph Lister (1867) 1st major antimicrobial chemical used Toxic and irritating side effects
Effects of UV radiation
>> UV light energy is absorbed by DNA >> Form pyrimidine dimers: {+} Abnormal linkages between adjacent pyrimidines (T and C) {+} nInterfere with normal DNA replication and transcription {+} Lead to inhibition of growth and death
Autoclave — moist heat methods
>> chamber that allows the use of steam under pressure to sterilize materials {+} similar to a pressure cooker >> common autoclave method: {+} 10-40 minutes at 121˚C
Microbial control methods
Can be broken into 3 categories: *[1.] physical agents* >> *heat* {+} dry [•] incineration [-] sterilization [•] dry ovens [-] sterilization {+} moist [•] steam under pressure [-] sterilization [•] boiling water, hot water, & pasteurization [-] disinfection >> *radiation* {+} ionizing [•] X rays, cathode rays, gamma rays [-] sterilization {+} nonionizing [•] UV rays [-] disinfection *[2.] chemical agents* >> *gases* [-] sterilization [-] disinfection >> *liquids* {+} on animate objects [-] antisepsis {+} on inanimate objects [-] disinfection [-] sterilization *[3.] mechanical removal methods* >> *filtration* {+} air [-] decontamination {+} liquids [-] sterilization
List and describe the actions of microbicidal or -cidal 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 Microbicidal - kills microbes; incineration, bactericidal antibiotics, chlorine, ROS, iodine, phenolics, heavy metals, strong acid/base, etc.
Types of germicides
High-Level Germicides Kill endospores Sterilant if used properly Used on critical items that are not heat-sterilizable (catheters, heart-lung equipment, implants) Intermediate-Level Germicides Kills fungal spores and some pathogens Do not kill bacterial spores Used to disinfect semi-critical items (respiratory equipment, thermometers) Low-Level Germicides Eliminates only vegetative bacteria/fungi, some viruses Used to clean non-critical materials: electrodes, straps, etc. Modes of action of germicides are to attack cellular targets: Proteins Nucleic acids Cell wall Cell membrane
Decontamination/sanitization — microbial control methods
The mechanical removal of most microbes and debris from an animate or inanimate surface (washing hands with soap (a sanitizer)) compare sterile fork with food on it vs. decontaminated fork without food on it. "Sanitizer" Any cleansing technique that mechanically removes microbes and debris Reduces contamination to safe levels Sanitizer: a soap or detergent used to sanitize
Antisepsis/degermation — microbial control methods
The same as disinfection, but on a living surface Application of chemical agents (antiseptics) to exposed body surfaces, wounds, and surgical incisions to destroy or inhibit vegetative pathogens Antiseptics (iodine, H2O2, washing hands with germicide) Sepsis: the growth of microorganisms in blood and other tissues Asepsis: any practice that prevents the entry of infectious agents into sterile tissues and prevents infection Aseptic techniques Sterile methods that exclude all microbes Antisepsis: application of chemical agents (antiseptics) to exposed body surfaces, wounds, and surgical incisions to destroy or inhibit vegetative pathogens 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
Disinfection — microbial control methods
destroys most microbial life Reduces contamination on inanimate surfaces Destroys vegetative cells but does not destroy endospores Examples: 5% bleach, boiling, iodine solutions
Define the term surfactant and explain this antimicrobial's mode of action. — chemicals with surface action: detergents
o Amphipathic properties of surfactants promote disruption of phospholipid bilayer Surfactants: Surface-active agent that forms a water-soluble interface. Limited microbicidal power Activity due to amphipathic nature of the molecule Disrupt selective permeability of cytoplasmic membrane Varied effects Anionic and cationic (more effective of the two) Surfactants are compounds that lower the surface tension between two liquids or between a liquid and a solid.
Identify applications for ethylene oxide sterilization.
o Chemiclave (sterilizes and disinfects delicate instruments) Ethylene oxide: Chemiclave: chemical sterilization (sporicidal) Reacts vigorously with DNA and proteins Explosive, carcinogen Causes damage to lungs, eyes, and mucous membranes Sterilizes and disinfect plastic and delicate hospital instruments
Identify advantages and disadvantages of cold treatment and desiccation.
*—ADVANTAGE:—* >> slows growth in food processing *—DISADVANTAGE:—* >> does not kill microbes —COLD TREATMENT— >> *merely impedes the activities* of most microbes {+} some microbes killed by cold temperatures {+} *most are not adversely affected* by: [•] gradual cooling [•] long-term refrigeration [•] deep freezing —DESICCATION— >> dehydration of vegetative cells directly exposed to normal room air {+} some delicate pathogens killed {+} some pathogens preserved >> can preserve foods because: {+} reduces the amount of water available to support microbial growth *—IMPORTANT:—* >> Chilling, freezing, and desiccation should not be considered as methods of disinfection or sterilization —LYOPHILIZATION— >> *combination of freezing and drying* >> common method of preserving microbes and other cells in a viable state >> pure cultures are frozen instantaneously and exposed to a vacuum that removes water
Identify the types of microorganisms in order from least resistant to most resistant to microbial control measures/agents
*—LEAST—* >> enveloped viruses >> most gram-positive bacteria >> nonenveloped viruses >> fungi and fungal spores >> most gram-negative bacteria >> protozoan trophozoites >> protozoan cysts >> Staphylococcus and Pseudomonas >> Mycobacterium >> bacterial endospores >> prions *—MOST—*
Compare and contrast moist and dry heat methods of control and identify multiple examples of each.
*—MOIST—* >> temperature ranges from *60°C to 135°C* >> lower temperatures and shorter exposure times than dry heat >> most microbicidal effect is *coagulation and denaturation of proteins* to permanently halt microbial metabolism —EXAMPLES— [•] hot water, boiling water [•] pasteurization [•] steam {+} at sea level (1 ATM = 15 psi): [-] water boils and makes steam which is 100 ˚C {+} increasing pressure increases the temp at which steam is generated [-] temperature of steam at various psi: [o] 20 psi = 109 ˚C [o] 25 psi = 115 ˚C [o] 30 psi = 121 ˚C [•] autoclave *—DRY—* >> air with a low moisture content that has been heated by a flame or electric heating coil >> higher temperature ranges from *160 °C to several thousand ˚C* >> at high temperatures, dry heat oxidizes cells, burning them to ashes —EXAMPLES— [•] incineration [•] drying oven
Differentiate between the two types of radiation control methods and provide an application of each.
*—RADIATION—* >> energy emitted from atomic activities and dispersed at high velocity through matter or space —IRRADIATION— >> bombardment of microbes with radiation *—IONIZING—* Radiation ejects orbital electrons from an atom, causing ions to form Damages proteins Gamma rays, X-rays, electrons >> works on endospores —EXAMPLES:— [•] gamma rays [•] electrons [•] X-rays — high speed electrons cause DNA breaks [=] *cold sterilization* [-] effective alternative for sterilizing materials [-] works well on items sensitive to heat or chemicals *—NONIONIZING—* >> excites atoms, raising them to a higher energy state (no ions formed) >> leads to the formation of abnormal bonds within molecules such as DNA >> UV is not as penetrating, requires longer exposure times [-] *UV rays* = disinfection
Incineration and hot air — dry heat methods
*—dry heat temps and time are much higher—* >> bunsen burner: 1870 ˚C >> incineration: 800 - 6500 ˚C [•] recontamination [•] specimen spatter >> hot air oven: 2- 4 hrs at 150 - 180 ˚C
Name the desirable characteristics of chemical control agents.
>> *rapid action* [-] in low concentrations >> *soluble* [-] in water or alcohol >> *stable* [-] long -term >> *broad spectrum* [-] microbicidal action without toxicity to human and animal tissues >> *penetrating* [-] of inanimate surfaces to sustain a cumulative or persistent action >> *resistant* to becoming inactivated [-] by organic matter >> *non-corrosive* [-] or non staining properties >> *sterilizing* >> *deodorizing* >> *affordable* [-] and ready availability >> no single germicide fits all of these categories {+} levels = high, intermediate, low
Ultraviolet (UV) radiation — nonionizing radiation
>> most lethal from 240 - 280 nm, peak 260 nm [•] UV germicidal lamps — generates 254 nm >> *SPECIFIC damage is at pyrimidine bases* {+} thymine {+} cytosine *[•] UV causes PYRIMIDINE DIMERS* [-] affect DNA replication >> *not as penetrating as ionizing radiation:* {+} passes readily through air, slightly through liquids, and only poorly through solids >> object to be disinfected must be directly exposed to it for full effect >> creates photochemical products — —such as— [•] free radicals [•] damages proteins
List the 4 outcomes of microbial control outside the body
>> sterilization >> disinfection >> antisepsis >> decontamination
Iodine — halogen antimicrobial agents
All classes of organisms are killed by iodine if proper concentrations and exposure times are used Penetrates cells Disrupts hydrogen and disulfide bonding Disrupts metabolic functions Not adversely affected by organic matter and pH There are different types of iodine solutions (next slide) Do you think iodine kills endospores? 2 Forms of Iodine: Free iodine (I_2 ) Iodophors - iodine complexed with a solubilizing agent (such as a surfactant); result is a water-soluble material that releases free iodine when in solution. Applications Aqueous iodine: Topical antiseptic, treatment for burned and infected skin, or before surgery (example: 2% iodine+ 2.4% sodium iodide) Iodine tincture: Used in skin antisepsis (2% iodine + 70% alcohol) Iodine tablets: Used for disinfecting water Iodophors: Complex of iodine and alcohol (Betadine, Povidone, Isodine) Slowly release free iodine (increase penetration) Have replaced free iodine solutions in medical antisepsis Iodine can be toxic when absorbed, so no longer considered safe for routine antiseptics Iodophors release iodine slowly
Applications of phenolics
Cresols: Phenolic derivatives combined with soap (example: Lysol) Bisphenols: Aerosol sprays and cleansing soaps Triclosan: Disinfectant and antiseptic chemical added to many products Chlorhexidine: Hand scrubbing, surgical prep, and other medical uses Products: Hibiclens, Hibitane, Peridex Targets cell membranes and protein structures Mild, low toxicity, rapid action Chlorohexidine: bactericidal for gram (-) and gram (+), INACTIVE against endospores Phenol- ring with -OH, causes chemical burns, highly reactive Phenolics: one or more aromatic (ring shaped) carbon rings with added functional groups Cresols - are "alkylated" (-CH3) (smallest alkyl group is methyl) (usually combined with soap) Used in cesspools, drains, animal quarters Example: LYSOL Orthophenyl pheol - aerosol sprays (Bis phenols) TRICLOSAN!! Dichlorophenoxyphenol - LOTS of products have this ------------------ All phenolics contain a basic aromatic ring, but they differ in the types of additional compounds such as Cl and CH3.
Chlorine —halogen antimicrobial agents
Liquid and gaseous chlorine (Cl_2 ), hypochlorites (ClO-), and chloramines (NH_2 Cl) Kill bacteria, endospores, fungi, viruses Less effective if exposed to light, alkaline pH, and excess organic matter Hypochlorites: Broadly used in industry and allied health Household bleach is a weak solution of sodium hypochlorite Sanitize and disinfect pools, water, food, canning equipment, etc. Chloramines: Used as alternatives to pure chlorine in water treatment Clorox® "Bleach-free" cleaners Hypochlorous acid (HOCl) oxidizes sulfhydryl groups (S-H) and forms disulfide bonds Less effective if exposed to light MY FAVORITE house hold cleaning product (5% bleach) In drinking water, sewage treatment, Chloramines may be safer since they do not produce cancer causing substances (like trihalomethanes)
List the actions of microbistatic or -static agents
Microbes are prevented from multiplying but are not killed Bacteristatic agents: Prevent the growth of bacteria on tissues or objects in the environment Fungistatic chemicals: Inhibit fungal growth Microbistatic agents: Chemicals used to control microorganisms in the body (antiseptics and drugs) Microbistatic - slows growth; cold, bacteriostatic antibiotics, preservatives, etc.
Discuss the advantages and disadvantages of aldehyde agents in microbial control.
o Advantage: rapid, broad spectrum, potent, sterilizing o Disadvantage: extremely toxic Glutaraldehyde: Rapid, broad spectrum, accepted as a sterilant Retains potency in the presence of organic matter Sterilizes materials damaged by heat Formaldehyde: Formalin: aqueous solution Intermediate- to high-level disinfectant Extremely toxic Kills endospores
List advantages and disadvantages to the use of phenolic compounds as control agents.
o Advantage: strong, act in presence of organic matter, destroy vegetative cells and most viruses o Disadvantage: not guaranteed to kill endospores, may be toxic o Example: Triclosan Phenolics STRONG! Destroy vegetative bacteria, fungi, and most viruses Not guaranteed to kill endospores (not sterilizing) Able to act in the presence of organic matter Detergent action (surfactant) Many are too toxic to use as antiseptics Disinfectant aerosol sprays
Explain the mode of action of alcohols and their limitations as effective antimicrobials.
o Denature proteins and destroy membranes o Destroy vegetative cells but not endospores Ethanol (ethyl alcohol) and Propanol (propyl alcohol) Destroys vegetative microbial forms but does not kill endospores Tuberculocidal Denature proteins Greater efficacy at 70% than at 100% More effective against enveloped than nonenveloped viruses Skin degerming and disinfection Vapors may affect nervous system Disrupt cell surface tension Compromise membrane integrity Denatures proteins Water is needed for proteins to coagulate, higher than 70% doesn't work as well than a lower conc. Gels and foams are generally 60-70% alcohol, to be Microbicidal needs to be exposed to skin for 30 sec.
Identify examples of some heavy metal control agents and their most common applications.
o Mercury tinctures (antiseptics, preservative), silver nitrate (topical germicide, incorporated into textiles), amalgam (silver + mercury) Oligodynamic (Toxic in minute quantities) Example: mercury and silver compounds have significance as germicides Bind to functional groups of proteins Drawbacks: Toxic to humans if ingested Cause allergic reactions Neutralized by biological wastes Microbes can develop resistance to microbes Weak organic mercury tinctures: Effective antiseptics and infection preventives Preservatives in cosmetic and ophthalmic solutions Silver compounds: Silver nitrate: topical germicide Silver sulfadiazine: burn treatment Pure silver: incorporated into catheters Colloidal silver: mild germicide Silver ions: incorporated into hard surfaces and textiles
Pinpoint the most appropriate applications of hydrogen peroxide agents.
o Microbicidal (at high concentrations) o Examples: Hydrogen peroxide, ozone Hydrogen peroxide (𝐇_𝟐 𝐎_𝟐 ): Germicidal effects are due to toxic Reactive Oxygen (free radicals ●OH) Bactericidal, virucidal, fungicidal, and sporicidal at high concentrations (may kill endospores) Antiseptic: Skin and wound cleansing, bedsore care, mouthwashes Disinfectant: Soft contacts, surgical implants, plastic equipment, utensils, bedding, and room interiors Vaporized hydrogen peroxide: Used for small industrial items and larger enclosed spaces Sporicidal
Sterilization — microbial control methods
the destruction of all microbial life (including endospores) Surgical instruments, Syringes, Commercially packaged foods
Outline the process of filtration and describe its two advantages in microbial control.
—ADVANTAGES—decontamination *[1.]* removes microbes from air or liquid *[2.]* sterilize or disinfect liquids that cannot be heated Most filters are perforated by precise, uniform pores: Allows selection of minimum particle size to be trapped Even smaller pore diameters permit true sterilization by removing viruses and even large proteins 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
Boiling water and pasteurization — moist heat methods
—BOILING WATER— >> *disinfection ONLY* {+} no sterilization >> endospores survive >> disadvantage: *[•] easily recontaminated* when removed from water >> exposing to 100°C (boiling water) for 30 minutes {+} kill most non-endospore-forming pathogens, including resistant species —such as— [•] tubercle bacillus [•] staphylococci —PASTEURIZATION— >> technique where heat is applied to liquids to kill potential agents of infection and spoilage while retaining the liquids flavor and food value >> FLASH method: {+} 15 seconds at 72 °C {+} less likely to damage flavor >> BATCH method: {+} 30 min at 63-66 °C >> All non-heat resistant forms of bacteria, yeast, molds, protozoa, worms, and viruses are killed by *80 °C for 20 mins* [•]
Name six methods of physical control of microorganisms.
—HEAT most widely used method— *[1.]* Heat {+} moist {+} dry *[2.]* cold *[3.]* radiation {+} ionizing {+} nonionizing *[4.]* desiccation/lyophilization *[5.]* osmotic pressure *[6.]* filtration
Identify some common uses of osmotic pressure as a control method.
—OSMOTIC PRESSURE— >> preserving food via hypertonicity causing plasmolysis >> adding large amounts of salt or sugar to foods creates a *hypertonic environment* >> *causes plasmolysis* in bacteria >> impossible for microbes to multiply —COMMON USES— >> "cured" meats {+} treated with high salt concentrations so they can be kept for long periods without refrigeration >> high sugar in jams and jellies has the same effect