ZO 211 Week 4 lecture
- 1. ©McGraw-Hill Education Week 4 Lecture (Chapter 9, 10 & 11)
- 2. ©McGraw-Hill Education Physical and Chemical Control of Microbes
- 3. ©McGraw-Hill Education Concepts in Antimicrobial Control Term Definition Key Points Examples of Agents Sterilization Process that destroys or removes all viable microorganisms (including viruses) The term sterile should be used only in the strictest sense to refer to materials that have been subjected to the process of sterilization (there is no such thing as slightly sterile) Generally reserved for inanimate objects as it would be impractical or dangerous to sterilize parts of the human body Common uses: surgical instruments, syringes, commercially packaged food Heat (autoclave) Sterilants (chemical agents capable of destroying endospores) Disinfection Physical process or a chemical agent to destroy vegetative pathogens but not bacterial endospores Removes harmful products of microorganisms (toxins) from material Normally used on inanimate objects because the concentration of disinfectants required to be effective is harmful to human tissue Common uses: boiling food utensils, applying 5% bleach solution to an examining table, immersing thermometers in an iodine solution between uses Decontamination/ Sanitization Cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels Important to restaurants, dairies, breweries, and other commercial entities that handle large numbers of soiled utensils/containers Common uses: Cooking utensils, dishes, bottles, and cans must be sanitized for reuse Antisepsis/ Degermation Reduces the number of microbes on the human skin A form of decontamination but on living tissues Involves scrubbing the skin (mechanical friction) or immersing it in chemicals (or both) Alcohol Surgical hand scrubs
- 4. ©McGraw-Hill Education Microbial Control Methods Jump to long description
- 5. ©McGraw-Hill Education Relative Resistance of Different Microbial Types to Microbial Control Agents Jump to long description
- 6. ©McGraw-Hill Education Comparative Resistance of Bacterial Endospores and Vegetative Cells to Control Agents Method Required to Destroy Endospores Required to Destroy Vegetative Forms Endospores Are _____ x More Resistant Heat (moist) 120°C 80°C 1.5 Radiation (X-ray) dosage 4,000 Grays 1,000 Grays 4 Sterilizing gas (ethylene oxide) 1,200 mg/L 700 mg/L 1.7 Sporicidal liquid (2% glutaraldehyde) 3 h 10 min 18
- 7. ©McGraw-Hill Education Agents versus Processes(1) Sterilization and disinfection: processes Agents used in the process • Bactericide: chemical that destroys bacteria except for those in the endospore stage • Fungicide: chemical that can kill fungal spores, hyphae, yeasts • Virucide: chemical known to inactivate viruses, especially on living tissue • Sporicide: an agent capable of destroying bacterial endospores • Germicide/microbicide: chemical agents that kill microorganisms
- 8. ©McGraw-Hill Education Agents versus Processes(2) Sepsis: the growth of microorganisms in the blood and other tissues Asepsis: • Any practice that prevents the entry of infectious agents into sterile tissues and thus prevents infection • Aseptic techniques: practiced in health care; range from sterile methods to antisepsis
- 9. ©McGraw-Hill Education Agents versus Processes(3) Antiseptics: chemical agents applied directly to exposed body surfaces (skin and mucous membranes), wounds, and surgical incisions to prevent vegetative pathogens • Preparing the skin before surgical incisions with iodine compounds • Swabbing an open root canal with hydrogen peroxide • Ordinary hand washing with a germicidal soap
- 10. ©McGraw-Hill Education Agents versus Processes(4) Stasis and static mean “to stand still” Bacteristatic: chemical agents that prevent the growth of bacteria on tissues or on objects in the environment Fungistatic: chemicals that inhibit fungal growth Antiseptics and drugs often have microbistatic effects because microbicidal compounds can be toxic to human cells Even a -cidal agent does not necessarily result in sterilization, depending on how it is used
- 11. ©McGraw-Hill Education Microbial Control on Medical Devices Critical medical devices: • Expected to come into contact with sterile tissues • Must be sterilized before use Semicritical devices: • Come into contact with mucosal membranes • Must receive high-level disinfection, preferably sterilized Noncritical devices: • Do not touch the patient or only touch intact skin • Require only low-level disinfection unless they become contaminated with blood or body fluids
- 12. ©McGraw-Hill Education What Is Microbial Death? Death: permanent termination of an organism’s vital processes Microbes have no conspicuous vital processes; therefore, death is difficult to determine Permanent loss of reproductive capability, even under optimum growth conditions, has become the accepted microbiological definition of death
- 13. ©McGraw-Hill Education Factors Affecting Death Rate Death of the whole population is not instantaneous: • Begins when a certain threshold of microbicidal agent is met • Death continues in a logarithmic manner as the time or concentration is increased • Active cells tend to die more quickly than less metabolically active cells • Eventually, a point is reached at which survival of any cells is highly unlikely; this point is equivalent to sterilization
- 14. ©McGraw-Hill Education Factors That Influence the Action of Antimicrobial Agents(1) The number of microbes: • Higher load of contaminants takes longer to destroy The nature of the microorganisms in the population: • Target population is usually a mixture of bacteria, fungi, spores, and viruses with broad spectrum of resistance Temperature and pH of the environment
- 15. ©McGraw-Hill Education Factors That Influence the Action of Antimicrobial Agents(2) The concentration (dose, intensity) of the agent: • UV radiation is most effective at 260 nm • Most disinfectants are more active at higher concentrations The mode of action of the agent: • How does it kill or inhibit the microorganism? The presence of solvents, interfering organic matter, and inhibitors: • Saliva, blood, and feces can inhibit the actions of disinfectants and even of heat
- 16. ©McGraw-Hill Education Actions of Various Physical and Chemical Agents upon the Cell Cellular Target Effects of Agents Examples of Agents Used Cell wall Chemical agents can damage the cell wall by • blocking its synthesis, or • digesting it Chemicals Detergents Alcohol Cytoplasmic membrane Agents physically bind to lipid layer of the cytoplasmic membrane. This opens up the cytoplasmic membrane and allows damaging chemicals to enter the cell and important ions to exit the cell. Detergents Cellular synthesis Agents can interrupt the synthesis of proteins via the ribosomes, inhibiting proteins needed for growth and metabolism and preventing multiplication. Agents can change genetic codes (mutation). Formaldehyde Radiation Ethylene oxide Proteins Some agents are capable of denaturing proteins (breaking of protein bonds, which results in breakdown of the protein structure). Agents may attach to the active site of a protein, preventing it from interacting with its chemical substrate. Moist heat Alcohol Phenolics
- 17. ©McGraw-Hill Education Methods of Physical Control: Heat Elevated temperatures are microbicidal Lower temperatures are microbistatic Moist heat: hot water, boiling water, or steam between 60°C and 135°C Dry heat: hot air or an open flame, which ranges from 160°C to several thousand degrees C
- 18. ©McGraw-Hill Education Action of Heat and Chemicals on Proteins Jump to long description
- 19. ©McGraw-Hill Education Comparison of Times and Temperatures to Achieve Sterilization with Moist and Dry Heat Temperature (°C) Time to Sterilize (Min) Moist heat 121 15 125 10 134 3 Dry heat 121 600 140 180 160 120 170 60
- 20. ©McGraw-Hill Education Heat Resistance and Thermal Death: Endospores and Vegetative Cells Bacterial endospores: • Exhibit greatest resistance • Destruction of spores usually requires temperatures above boiling Vegetative cells: • Vary in sensitivity to heat • Death times vary from 50°C for 3 minutes to 60°C for 60 minutes
- 21. ©McGraw-Hill Education Thermal Death Measurements Thermal death time (TDT): shortest length of time required to kill all test microbes at a specified temperature Thermal death point (TDP): the lowest temperature required to kill all microbes in a sample in 10 minutes Heat treatment of perishable substances must render the product free of agents of spoilage or disease without affecting the speed and cost of processing
- 22. ©McGraw-Hill Education Moist Heat Methods(1) Boiling Water: Disinfection Pasteurization: Disinfection of Beverages Top left: ©McGraw-Hill Education/Charles D. Winters, photographer; Bottom left: ©James King-Holmes/Science Source Top right: ©John A. Rizzo/Getty Images Jump to long description
- 23. ©McGraw-Hill Education Moist Heat Methods(2) ©DenGuy/Getty Images Jump to long description
- 24. ©McGraw-Hill Education Dry Heath Methods Incineration Hot Air Oven Top: ©UIG via Getty Images; Bottom: ©RayArt Graphics/Alamy Stock Photo Jump to long description
- 25. ©McGraw-Hill Education The Effects of Desiccation and Lyophilization Desiccation: • Vegetative cells directly exposed to normal room temperature gradually become dehydrated • Some microbes are killed by desiccation; many others are not killed and some are even preserved Lyophilization: • Combination of freezing and drying • Method of preserving microorganisms in a viable state for many years • Pure cultures are frozen instantaneously and exposed to a vacuum that removes water, avoiding the formation of ice crystals
- 26. ©McGraw-Hill Education Radiation Energy emitted from atomic activities and dispersed at high velocity through matter or space: • Gamma rays • X rays • Ultraviolet radiation Jump to long description
- 27. ©McGraw-Hill Education Formation of Pyrimidine Dimers by the Action of UV Radiation Jump to long description
- 28. ©McGraw-Hill Education Filtration Effective method to remove microbes from air and liquids: • Fluid is strained through a filter with openings large enough for the fluid to pass, but too small for microbes • Also used are thin membranes of cellulose acetate, polycarbonate, and plastics whose pore size is carefully controlled • Charcoal, diatomaceous earth, or unglazed porcelain are also used • Pore sizes can be controlled to permit true sterilization by trapping viruses or large proteins
- 29. ©McGraw-Hill Education Uses of Filtration Used to prepare liquids that cannot withstand heat such as serum, blood products, vaccines, drugs, IV fluids, enzymes, and media Alternative method for decontaminating milk and beer without altering their flavor Important step in water purification Unable to remove soluble molecules (toxins) that can cause disease High-efficiency particulate air (HEPA) filters are used in hospital rooms and sterile rooms
- 30. ©McGraw-Hill Education Membrane Filtration Jump to long description Source: CDC/Dr. Ray Butler; Janice Carr (b)
- 31. ©McGraw-Hill Education Osmotic Pressure Adding large amounts of salt or sugar to foods creates a hypertonic environment for bacteria, causing plasmolysis Pickling, smoking, and drying foods have been used for centuries to preserve foods Osmotic pressure is never a sterilizing technique
- 32. ©McGraw-Hill Education Chemical Agents in Microbial Control Occur in the liquid, gaseous, or solid state Range from disinfectants and antiseptics to sterilants and preservatives Aqueous: chemicals dissolved in pure water as the solvent Tinctures: chemicals dissolved in pure alcohol or water-alcohol mixtures
- 33. ©McGraw-Hill Education Desirable Qualities in a Germicide Rapid action, even in low concentrations Solubility in water or alcohol and long-term stability Broad-spectrum microbicidal action without being toxic to human and animal tissues Penetration of inanimate surfaces to sustain a cumulative or persistent action Resistance to becoming inactivated by organic matter Not corrosive and nonstaining Sanitizing and deodorizing properties Affordability and availability
- 34. ©McGraw-Hill Education High-, Intermediate-, and Low-Level Germicides Germicides are evaluated in terms of their effectiveness in destroying microbes in medical and dental settings: • High-level germicides kill endospores and can be used as sterilants • Intermediate-level germicides kill fungal, but not bacterial, spores, resistant pathogens, and viruses • Low-level germicides eliminate only vegetative bacteria, vegetative fungal cells, and some viruses
- 35. ©McGraw-Hill Education Factors Affecting the Germicidal Activity of Chemicals Nature of the microorganisms being treated Nature of the material being treated Degree of contamination Time of exposure Strength and chemical action of the germicide
- 36. ©McGraw-Hill Education Required Concentrations and Times for Chemical Destruction of Selected Microbes Organism Concentration Time Agent: Chlorine Mycobacterium tuberculosis 50 ppm 50 sec Entamoeba cysts (protozoa) 0.1 ppm 150 min Hepatitis A virus 3 ppm 30 min Agent: Ethyl Alcohol Staphylococcus aureus 70% 10 min Escherichia coli 70% 2 min Poliovirus 70% 10 min Agent: Hydrogen Peroxide Staphylococcus aureus 3% 12.5 sec Neisseria gonorrhoeae 3% 0.3 sec Herpes simplex virus 3% 12.8 Agent: Quaternary Ammonium Compound Staphylococcus aureus 450 ppm 10 min Salmonella typhi 300 ppm 10 min Agent: Ethylene Oxide Gas Streptococcus faecalis 500 mg/L 2 to 4 min Influenza virus 10,000 mg/L 25 h
- 37. ©McGraw-Hill Education Germicidal Categories According to Chemical Group(1) Agent Target Microbes Form(s) Mode of Action Indicators for Use Limitations Halogens: chlorine Can kill endospores (slowly); all other microbes Liquid/gaseous chlorine (Cl2), hypochlorites (OCl), chloramines (NH2Cl) In solution, these compounds combine with water and release hypochlorous acid (HOCl); denature enzymes permanently and suspend metabolic reactions Chlorine kills bacteria, endospores, fungi, and viruses; gaseous/liquid chlorine: used to disinfect drinking water, sewage and waste water; hypochlorites: used in health care to treat wounds, disinfect bedding and instruments, sanitize food equipment and in restaurants, pools, and spas; chloramines: alternative to pure chlorine in treating drinking water; also used to treat wounds and skin surfaces Less effective if exposed to light, alkaline pH, and excess organic matter Halogens: iodine Can kill endospores (slowly); all other microbes Free iodine in solution (I2); Iodophors (complexes of iodine and alcohol) Penetrates cells of microorganisms where it interferes with a variety of metabolic functions; interferes with the hydrogen and disulfide bonding of proteins 2% iodine, 2.4% sodium iodide (aqueous iodine) used as a topical antiseptic; 5% iodine, 10% potassium iodide used as a disinfectant for plastic and rubber instruments, cutting blades, etc.; Iodophor products contain 2% to 10% of available iodine, which is released slowly; used to prepare skin for surgery, in surgical scrubs, to treat burns, and as a disinfectant Can be extremely irritating to the skin and is toxic when absorbed; many iodophors banned in consumer products in 2017.
- 38. ©McGraw-Hill Education Germicidal Categories According to Chemical Group(2) Agent Target Microbes Form(s) Mode of Action Indicators for Use Limitations Oxidizing agents Kill endospor es and all other microbes Hydrogen peroxide, peracetic acid Oxygen forms free radicals (–OH), which are highly toxic and reactive to cells As an antiseptic, 3% hydrogen peroxide used for skin and wound cleansing, mouth washing, bedsore care; used to treat infections caused by anaerobic bacteria; 35% hydrogen peroxide used in low temperature sterilizing cabinets for delicate instruments Sporicidal only in high concentrations Aldehydes Kill endospor es and all other microbes Organic substances bearing a –CHO functional group on the terminal carbon Glutaraldehyde can irreversibly disrupt the activity of enzymes and other proteins within the cell; ortho- phthalaldehyde Glutaraldehyde kills rapidly and is broad-spectrum; used to sterilize respiratory equipment, scopes, kidney dialysis machines, dental instruments; ortho- phthalaldehyde is safer than glutaraldehyde and just as effective Glutaraldehyd e is somewhat unstable, especially with increased pH and temp; ortho- phthalaldehyd e is much more expensive than glutaraldehyde
- 39. ©McGraw-Hill Education Germicidal Categories According to Chemical Group(3) Agent Target Microbes Form(s) Mode of Action Indicators for Use Limitations Gaseous sterilants/ disinfectan ts Ethylene oxide kills endospore ; other gases less effective Ethylene oxide is a colorless substance that exists as a gas at room temperature Ethylene oxide reacts vigorously with functional groups of DNA and proteins, blocking both DNA replication and enzymatic actions; chlorine dioxide is a strong alkylating agent Ethylene oxide is used to disinfect plastic materials and delicate instruments; can also be used to sterilize syringes, surgical supplies, and medical devices that are prepackaged Ethylene oxide is explosive—it must be combined with a high percentage of carbon dioxide or fluorocarbon; it can damage lungs, eyes, and mucous membranes if contacted directly; ethylene oxide is rated as a carcinogen by the government Phenol (carbolic acid) Some bacteria, viruses, fungi Derived from the distillation of coal tar; phenols consist of one or more aromatic carbon rings with added functional groups In high concentrations, they are cellular poisons, disrupting cell walls and membranes, proteins; in lower concentrations, they inactivate certain critical enzyme systems Phenol remains one standard against which other (less toxic) phenolic disinfectants are rated; the phenol coefficient quantitatively compares a chemical’s antimicrobial properties to those of phenol; phenol is now used only in certain limited cases, such as in drains, cesspools, and animal quarters Toxicity of many phenolics makes them dangerous to use as antiseptics; many phenols banned in consumer products in 2017, including triclosan and triclocarban.
- 40. ©McGraw-Hill Education Germicidal Categories According to Chemical Group(4) Agent Target Microbes Form(s) Mode of Action Indicators for Use Limitations Chlorhexidine Most bacteria, viruses, fungi Complex organic base containing chlorine and two phenolic rings Targets bacterial membranes, where selective permeability is lost, bacterial cell walls, and proteins, resulting in denaturation Mildness, low toxicity and rapid action make chlorhexidine a popular choice of agents; used in hand scrubs, prepping skin for surgery, as an obstetric antiseptic, as a mucous membrane irrigant, etc. Effects on viruses and fungi are variable Alcohol Most bacteria, viruses, fungi Colorless hydrocarbons with one or more –OH functional groups; ethyl and isopropyl alcohol are suitable for antimicrobial control Concentrations of 50% and higher dissolve membrane lipids, disrupt cell surface tension, and compromise membrane integrity Germicidal, nonirritating, and inexpensive; routinely used as skin degerming agents (70% to 95% solutions) Rate of evaporation decreases effectiveness; inhalation of vapors can affect the nervous system
- 41. ©McGraw-Hill Education Germicidal Categories According to Chemical Group(5) Agent Target Microbes Form(s) Mode of Action Indicators for Use Limitations Detergents Some bacteria, viruses, fungi Polar molecules that act as surfactants; anionic detergents have limited microbial power; cationic detergents, such as quaternary ammonium compounds (“quats”), are much more effective antimicrobials Positively charged end of the molecule binds well with the predominantly negatively charged bacterial surface proteins; long, uncharged hydrocarbon chain allows the detergent to disrupt the cytoplasmic membrane; cytoplasmic membrane loses selective permeability, causing cell death Effective against viruses, algae, fungi, and gram-positive bacteria; rated only for low-level disinfection in the clinical setting; used to clean restaurant utensils, dairy equipment, equipment surfaces, restrooms Ineffective against tuberculosis bacterium, hepatitis virus, Pseudomonas, and endospores; activity is greatly reduced in presence of organic matter; detergents function best in alkaline solutions; some quats banned in consumer products in 2017. Heavy metal compounds Some bacteria, viruses, fungi Heavy metal germicides contain either an inorganic or an organic metallic salt; may come in tinctures, soaps, ointment, or aqueous solution Mercury, silver, and other metals exert microbial effects by binding onto functional groups of proteins and inactivating them Organic mercury tinctures are fairly effective antiseptics; organic mercurials serve as preservatives in cosmetics, ophthalmic solutions, and other substances; silver nitrate solutions are used for topical germicides and ointments Microbes can develop resistance to metals; not effective against endospores; can be toxic if inhaled, ingested, or absorbed; may cause allergic reactions in susceptible individuals
- 42. ©McGraw-Hill Education Active Ingredients of Various Commercial Antimicrobial Products(1) Product Specific Chemical Agent Antimicrobial Category Lysol® Sanitizing Wipes Dimethyl benzyl ammonium chloride Detergent (quat) Clorox® Disinfecting Wipes Dimethyl benzyl ammonium chloride Detergent (quat) Tilex® Mildew Remover Sodium hypochlorites Halogen Lysol® Mildew Remover Sodium hypochlorites Halogen Ajax® Antibacterial Hand Soap Triclosan; banned beginning in fall 2017 Phenolic Dawn® Antibacterial Hand Soap Triclosan; banned beginning in fall 2017 Phenolic Dial® Antibacterial Hand Soap Triclosan; banned beginning in fall 2017 Phenolic Lysol® Disinfecting Spray Alkyl dimethyl benzyl ammonium saccharinate/ethanol Detergent (quats)/ alcohol
- 43. ©McGraw-Hill Education Active Ingredients of Various Commercial Antimicrobial Products(2) Product Specific Chemical Agent Antimicrobial Category ReNu® Contact Lens Solution Polyaminopropyl biguanide Chlorhexidine Wet Ones® Antibacterial Moist Towelettes Benzethonium chloride Detergents (quat) Noxema® Triple Clean Triclosan; banned beginning in fall 2017 Phenolic Scope® Mouthwash Ethanol Alcohol Purell® Instant Hand Sanitizer Ethanol Alcohol Pine-Sol® Phenolics and surfactant Mixed Allergan® Eye Drops Sodium chlorite Halogen
- 45. ©McGraw-Hill Education Principles of Antimicrobial Therapy The introduction of modern drugs to control infections was a medical revolution in the 1940s Antimicrobial drugs have reduced the incidence of certain infections, but they have not eradicated infectious diseases and probably never will Today, doctors are worried that we are dangerously close to a postantibiotic era, where the drugs we have are no longer effective
- 46. ©McGraw-Hill Education Antimicrobial Chemotherapy Goal of antimicrobial chemotherapy: • Administer a drug to an infected person that destroys the infective agent without harming the host’s cells A drug must be able to: • Be easy to administer and able to reach the infectious agent anywhere in the body • Be absolutely toxic to the infectious agent and absolutely nontoxic to the host • Remain active in the body as long as needed and be safely and easily broken down and excreted
- 47. ©McGraw-Hill Education Characteristics of the Ideal Antimicrobial Drug • Toxic to the microbe but nontoxic to host cells • Microbiocidal rather than microbiostatic • Relatively soluble; functions even when highly diluted in body fluids • Remains potent long enough to act and is not broken down or excreted prematurely • Does not lead to the development of antimicrobial resistance • Complements or assists the activities of the host’s defenses • Remains active in tissues and body fluids • Readily delivered to the site of infection • Reasonably priced
- 48. ©McGraw-Hill Education Terminology of Antimicrobials Prophylaxis Use of a drug to prevent infection of a person at risk Antimicrobial Chemotherapy The use of drugs to control infection Antimicrobials All-inclusive term for any antimicrobial drug, regardless of its origin Antibiotics Substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms; generally, the term is used for drugs targeting bacteria and not other types of microbes Semisynthetic Drugs Drugs that are chemically modified in the laboratory after being isolated from natural sources Synthetic Drugs Drugs produced entirely by chemical reactions Narrow-Spectrum (Limited Spectrum) Antimicrobials effective against a limited array of microbial types—for example, a drug effective mainly against gram-positive bacteria Broad-Spectrum (Extended Spectrum) Antimicrobials effective against a wide variety of microbial types—for example, a drug effective against both gram-positive and gram-negative bacteria
- 49. ©McGraw-Hill Education Origins of Antimicrobial Drugs Antibiotics are natural metabolic products of bacteria and fungi: • Produced to inhibit the growth of competing microbes in the same habitat (antagonism) Greatest numbers derived from: • Bacteria in the genera Streptomyces and Bacillus • Molds in the genera Penicillium and Cephalosporium
- 50. ©McGraw-Hill Education Kirby-Bauer Technique Surface of an agar plate is spread with test bacterium Small discs containing a prepared amount of antibiotic are placed on the plate Zone of inhibition surrounding the discs is measured and compared with a standard for each drug Antibiogram provides data for drug selection This method is less effective for anaerobic, highly fastidious, or slow-growing bacteria
- 51. ©McGraw-Hill Education Results of a Sample Kirby-Bauer Test Drug Zone Size (mm) Required for Susceptibility (S) Zone Size (mm) Required for Resistance (R) Example Results for Staphylococcus aureus Evaluation Bacitracin >13 <8 15 Sensitive Chloramphenicol >18 <12 20 Sensitive Erythromycin >18 <13 15 Intermediate Gentamicin >13 <12 16 Sensitive Kanamycin >18 <13 20 Sensitive Neomycin >17 <12 12 Resistant Penicillin G >29 <20 10 Resistant Polymyxin B >12 <8 10 Intermediate Streptomycin >15 <11 11 Resistant Vancomycin >12 <9 15 Sensitive Tetracycline >19 <14 25 Sensitive
- 52. ©McGraw-Hill Education Disc Diffusion Tests (a) ©McGraw-Hill Education/Don Rubbelke, photographer Jump to long description
- 53. ©McGraw-Hill Education Alternative to the Kirby-Bauer Procedure CDC/Dr. Richard Facklam Jump to long description
- 54. ©McGraw-Hill Education Tube Dilution Test(1) More sensitive and quantitative than the Kirby-Bauer test Antimicrobial is diluted serially in tubes of broth Each tube is inoculated with a small uniform sample of pure culture, incubated, and examined Minimum inhibitory concentration (MIC): the smallest concentration (highest dilution) of drug that visibly inhibits growth • Useful in determining the smallest effective dosage and providing a comparative index against other antimicrobials
- 55. ©McGraw-Hill Education Tube Dilution Test(2) Jump to long description
- 56. ©McGraw-Hill Education Therapeutic Index The ratio of the dose of the drug that is toxic to humans as compared to its minimum effective (therapeutic) dose: • The smaller the ratio, the greater the potential for toxic drug reactions • TI = 1.1 is a risky choice • TI = 10 is a safer choice • The drug with the highest therapeutic index has the widest margin of safety
- 57. ©McGraw-Hill Education Before Prescribing an Antibiotic The physician must take a careful history before prescribing an antibiotic: • Preexisting conditions that might influence the activity of the drug or the response of the patient • History of allergy to a certain class of drugs • Underlying liver or kidney disease • Infants, the elderly, and pregnant women require special precautions • Intake of other drugs can result in increased toxicity or failure of one or more drugs • Some drug combinations have synergistic effects, may allow for reduced dosages
- 58. ©McGraw-Hill Education Goal of Antimicrobial Drugs Disrupt cell processes or structures of bacteria, fungi, or protozoa Inhibit virus replication Interfere with the function of enzymes required to synthesize or assemble macromolecules Destroy structures already formed in the cell Selectively toxic: kill or inhibit microbial cells without damaging host tissues
- 59. ©McGraw-Hill Education Interactions Between Drug and Microbe Drugs with excellent selective toxicity block the synthesis of the bacterial cell wall (penicillins): • Human cells lack the chemical peptidoglycan and are unaffected by the drug Drugs most toxic to humans: • Drugs that act upon a structure common to both the infective agent and the host cell (cytoplasmic membrane) • As characteristics of the infectious agent are more and more similar to the host cell, selective toxicity becomes more difficult to achieve
- 60. ©McGraw-Hill Education Mechanisms of Drug Action Goals of chemotherapy: disrupt the structure or function of an organism to the point where it can no longer survive Antimicrobial drug categories: • Inhibition of cell wall synthesis • Inhibition of nucleic acid structure and function • Inhibition of protein synthesis • Interference with cytoplasmic membrane structure and function • Inhibition of folic acid synthesis
- 61. ©McGraw-Hill Education Drugs That Target the Cell Wall Penicillins • Penicillins G and V • Ampicillin, carbenicillin, amoxicillin • Nafcillin, cloxacillin • Clavulanic acid Cephalosporins • Cefazolin • Cefaclor • Cephalexin, cefotaxime • Ceftriaxone • Cefepime • Cegtaroline Carbapenems • Doripenem, imipenem • Aztreonam Miscellaneous drugs that target the cell wall • Bacitracin • Isoniazid • Vancomycin • Fosfomycin tromethamine
- 62. ©McGraw-Hill Education Drugs That Target Protein Synthesis Aminoglycosides: insert on sites on the 30S subunit and cause the misreading of the mRNA, leading to abnormal proteins • Streptomycin Tetracyclines: block the attachment of tRNA on the A acceptor site and stop further protein synthesis • Tetracycline Glycylcyclines • Tigecycline Macrolides: inhibit translocation of the subunit during translation (erythromycin) • Erythromycin, clarithromycin, azithromycin Miscellaneous drugs that target protein synthesis • Clindamycin • Quinupristin + dalfopristin (Synercid) • Linezolid
- 63. ©McGraw-Hill Education Drugs That Target Folic Acid Synthesis Sulfonamides: interfere with folate metabolism by blocking enzymes required for the synthesis of tetrahydrofolate, which is needed by the cells for folic acid synthesis and eventual production of DNA, RNA, and amino acids • Sulfamethoxazole • Silver sulfadiazine • Trimethoprim
- 64. ©McGraw-Hill Education Drugs That Target DNA or RNA Sulfonamides: interfere with folate metabolism by blocking enzymes required for the synthesis of tetrahydrofolate, which is needed by the cells for folic acid synthesis and eventual production of DNA, RNA, and amino acids • Sulfamethoxazole • Silver sulfadiazine • Trimethoprim
- 65. ©McGraw-Hill Education Drugs That Target Cytoplasmic or Cell Membranes Polymyxins (colistins): interact with membrane phospholipids; distort the cell surface and cause leakage of protein and nitrogen bases, particularly in gram-negative bacteria • Polymyxin B • Daptomycin
- 66. ©McGraw-Hill Education Spectrum of Activity for Antibiotics Jump to long decription
- 67. ©McGraw-Hill Education Characteristics of Selected Penicillin Drugs Name Spectrum of Action Uses, Advantages Disadvantages Penicillin G Narrow Best drug of choice when bacteria are sensitive; low cost; low toxicity Can be hydrolyzed by penicillinase; allergies occur; requires injection Penicillin V Narrow Good absorption from intestine; otherwise, similar to Penicillin G Hydrolysis by penicillinase; allergies Methicillin, nafcillin Narrow Not usually susceptible to penicillinase Poor absorption; allergies; growing Resistance Ampicillin Broad Works on gram- negative bacilli Can be hydrolyzed by penicillinase; allergies; only fair absorption Amoxicillin Broad Gram-negative infections; good absorption Hydrolysis by penicillinase; allergies Azlocillin, mezlocillin, ticarcillin Very broad Effective against Pseudomonas species; low toxicity compared with aminoglycosides Allergies; susceptible to many beta-lactamases Jump to long decription
- 68. ©McGraw-Hill Education Bacteria in Biofilms Bacteria in biofilms behave differently than when they are free-living: • Often unaffected by antimicrobials • Antibiotics often cannot penetrate the sticky extracellular material surrounding biofilms • Bacteria in biofilms express a different phenotype and have different antibiotic susceptibility profiles than free-living bacteria
- 69. ©McGraw-Hill Education Antibiotics and Biofilms Biofilm treatment strategies: • Interrupting quorum sensing pathways • Daptomycin: shown success • Adding DNAse to antibiotics aids penetration through extracellular debris • Impregnating devices with antibiotics prior to implantation Some antibiotics cause biofilms to form at a higher rate than they normally would
- 70. ©McGraw-Hill Education Agents Used to Treat Fungal Infections Drug Group Drug Examples Action Macrolide polyenes Amphotericin B Bind to fungal membranes, causing loss of selective permeability; extremely versatile Can be used to treat skin, mucous membrane lesions caused by Candida albicans Injectable form of the drug can be used to treat histoplasmosis and Cryptococcus meningitis Azoles Ketoconazole, fluconazole, miconazole, and clotrimazole Interfere with sterol synthesis in fungi Ketoconazole—cutaneous mycoses, vaginal and oral candidiasis, systemic mycoses Fluconazole—AIDS-related mycoses (aspergillosis, Cryptococcus meningitis) Clotrimazole and miconazole—used to treat infections in the skin, mouth, and vagina Echinocandins Micafungin, caspofungin Inhibit fungal cell wall synthesis Used against Candida strains and aspergillosis Allylamines Terbinafine, naftifine Inhibit enzyme critical for ergosterol synthesis Used to treat ringworm and other cutaneous mycoses
- 71. ©McGraw-Hill Education Antimalarial Drugs Quinine: • Principal treatment of malaria for hundreds of years • Has been replaced by less toxic synthesized quinolones, chloroquine and primaquine • Several species of Plasmodium and many stages in its life cycle mean that no single drug is universally effective Artemisinin: • Has become the staple for malaria treatment in most parts of the world • Artemisinin combination therapy (ACT): artemisinin with quinine derivatives or other drugs
- 72. ©McGraw-Hill Education Chemotherapy for Other Protozoal Infections Metronidazole: widely used amoebicide: • Treats intestinal infections and hepatic disease caused by Entamoeba histolytica • Also treats Giardia lamblia and Trichomonas vaginalis Other drugs with antiprotozoal activities: • Quinacrine • Sulfonamides • Tetracyclines
- 73. ©McGraw-Hill Education Agents to Treat Helminthic Infections Mebendazole and albendazole inhibit microtubules of worms, eggs, and larvae Pyrantel paralyzes the muscles of intestinal roundworms Praziquantel: • Tapeworm and fluke infections Ivermectin: • Veterinary drug used for strongyloidiasis and oncocerosis in humans
- 74. ©McGraw-Hill Education Antimicrobial Resistance Drug resistance: • An adaptive response in which microorganisms begin to tolerate an amount of drug that would normally be inhibitory • Due to the genetic versatility and adaptability of microbial populations • Can be intrinsic as well as acquired
- 75. ©McGraw-Hill Education How Does Drug Resistance Develop? In the 1980s and 1990s scientists began to observe treatment failures on a large scale Microbes become newly resistant to a drug after one of the following occurs: • Spontaneous mutations in critical chromosomal genes • Acquisition of entire new genes or sets of genes via horizontal transfer from another species
- 76. ©McGraw-Hill Education Development of Drug Resistance
- 77. ©McGraw-Hill Education Resistance Through Horizontal Transfer Resistance (R) factors: plasmids containing antibiotic resistance genes Can be transferred through conjugation, transformation, or transduction Plasmids encoded with drug resistance are naturally present in microbes before they have been exposed to an antibiotic Transposons also duplicate and insert genes for drug resistance into plasmids Sharing of resistance genes accounts for the rapid proliferation of drug-resistant species
- 79. ©McGraw-Hill Education Mechanisms of Drug Resistance
- 80. ©McGraw-Hill Education Threats Urgent threats: • Clostridium difficile (C. diff) • Carbapenem-resistant Enterobacteriaceae (CRE) • Drug-resistant Neisseria gonorrhoeae Serious threats: • Multidrug-resistant Acinetobacter • Drug-resistant Campylobacter • Fluconazole-resistant Candida • Many more Concerning threats: • Vancomycin-resistant Staphylococcus aureus (VRSA) • Erythromycin-resistant Group A Streptococcus • Clindamycin-resistant Group B Streptococcus
- 81. ©McGraw-Hill Education Examples of Superinfection Urinary tract infection caused by E. coli treated with antibiotics: • Lactobacilli in the female vagina are killed by the broad- spectrum cephalosporin used to treat the UTI • Overgrowth of Candida albicans occurs, causing a vaginal yeast infection or oral thrush Antibiotic-associated colitis: • Oral therapy with tetracyclines, clindamycin, and broad- spectrum penicillins kills off normal biota of the colon • Overgrowth of Clostridium difficile invades the intestinal lining and releases toxins that cause diarrhea, fever, and abdominal pain
- 82. ©McGraw-Hill Education Role of Antimicrobials in Disrupting Microbial Biota and Causing Superinfections Jump to long descriptiona
- 83. ©McGraw-Hill Education Interactions Between Microbes and Humans
- 84. ©McGraw-Hill Education The Human Microbiome(1) Humans and other mammals have the form and physiology that they have due to having been formed in intimate contact with their microbes Human microbiome: • The sum total of all microbes found on and in a normal human • Critically important to the health and functioning of its host organism
- 85. ©McGraw-Hill Education Colonization, Infection, Disease For the most part, our resident microbiota colonize us for the long term and do not cause disease Infection: microbes get past host defenses, enter tissues, and multiply Disease: deviation from health; pathologic state that results when cumulative effects of infection damage or disrupt tissues and organs Infectious disease: a pathogenic state caused directly by microorganisms or their products
- 86. ©McGraw-Hill Education Colonization of the Fetus Until recently, the uterus and its contents were thought to be sterile during embryonic and fetal development: • Analysis of newborns’ stools sampled before their first meal show a diversity of bacteria • This indicates that their intestines are colonized in utero
- 87. ©McGraw-Hill Education Colonization of the Newborn Important source of microbiota for a newborn is its trip through the vagina: • Lactobacillus provides the baby with the necessary enzymes to digest milk • Other species protect the baby from skin disorders and other conditions Human milk contains around 600 species of bacteria, and sugars that are digested by healthy gut bacteria
- 88. ©McGraw-Hill Education Where Babies Get a Microbiome ©Jim Connely (ultrasound); ©Adam Gault/SPL/Getty Images (birth); ©Jose Luis Pelaez Inc/Blend Images LLC (breast feeding); ©Pixtal/SuperStock (bottle); ©Marc Romanelli/Blend Images (family) ©Kwame Zikomo/ Purestock/SuperStock (with dog); ©alexmak72427/iStock/Getty Images (scar)Jump to long description
- 89. ©McGraw-Hill Education Virulence Virulence: • Relative severity of a disease caused by a particular microbe • Degree of pathogenicity Virulence of a microbe is determined by its ability to: • Establish itself in a host • Cause damage Virulence factor: any characteristic or structure of the microbe that contributes to its ability to establish itself in the host and cause damage
- 90. ©McGraw-Hill Education Portal of Entry Organism/Disease How Access Is Gained Skin Staphylococcus aureus, Streptococcus pyogenes, Clostridium tetani Via nicks, abrasions, punctures, areas of broken skin Skin Herpes simplex (type 1) Via mucous membranes of the lips Skin Helminth worms Burrow through the skin Skin Viruses, rickettsias, protozoa (i.e., malaria, West Nile virus) Via insect bites Skin Haemophilus aegyptius, Chlamydia trachomatis, Neisseria gonorrhoeae Via the conjunctiva of the eye Gastrointestinal tract Salmonella, Shigella, Vibrio, Escherichia coli, poliovirus, hepatitis A, echovirus, rotavirus, enteric protozoans (Giardia lamblia, Entamoeba histolytica) Through eating/drinking contaminated foods and fluids Via fomites (inanimate objects contaminated with the infectious organism) Respiratory tract Bacteria causing meningitis, influenza, measles, mumps, rubella, chickenpox, common cold, Streptococcus pneumoniae, Klebsiella, Mycoplasma, Cryptococcus, Pneumocystis, Mycobacterium tuberculosis, Histoplasma Via inhalation of offending organism Urogenital tract HIV, Trichomonas, hepatitis B, syphilis, Treponema pallidum, Neisseria gonorrhoeae, Chlamydia trachomatis, herpes, genital warts Enter through the skin/mucosa of penis, external genitalia, vagina/cervix, urethra; may enter through an unbroken surface or through a cut or abrasion
- 91. ©McGraw-Hill Education Quantity of Microbes in the Inoculating Dose Infectious dose (ID): • The minimum number of microbes necessary to cause an infection to proceed • Microorganisms with smaller infectious doses have greater virulence • ID for Q fever is a single cell • ID for tuberculosis, giardiasis, and coccidioidomycosis is about 10 cells • ID for gonorrhea is 1,000 cells • ID for typhoid fever is 10,000 cells • ID for cholera is 1,000,000,000 cells
- 92. ©McGraw-Hill Education Adhesion Mechanisms Bacterial, fungal, and protozoal pathogens attach by: • Fimbriae (pili) • Surface proteins • Adhesive slimes or capsules Viruses attach by specialized receptors Parasitic worms fastened by suckers, hooks, and barbs
- 93. ©McGraw-Hill Education Step Three: Becoming Established— Surviving Host Defenses Phagocytes: cells that engulf and destroy host pathogens by means of enzymes and antimicrobial chemicals Antiphagocytic factors: • Virulence factors used by some pathogens to avoid phagocytes • Leukocidins: kill phagocytes outright • Extracellular surface layer (slime or capsule) makes it difficult for the phagocyte to engulf the pathogen • Some bacteria survive inside the phagocyte
- 94. ©McGraw-Hill Education Step Four: Causing Disease Virulence factors are simply adaptations a microbe uses to establish itself in a host Three ways that microorganisms cause damage to their host: • Directly through the action of enzymes or toxins (both endotoxins and exotoxins) • Indirectly by inducing the host’s defenses to respond excessively or inappropriately • Epigenetic changes made to host cells by microbes
- 95. ©McGraw-Hill Education Exotoxins Hemolysins: class of bacterial exotoxin that disrupts the cell membrane of red blood cells • Cause the RBC to hemolyze, to burst and release hemoglobin pigment ©McGraw-Hill Education/Lisa Burgess, photographer Jump to long description
- 96. ©McGraw-Hill Education Endotoxin Lipopolysaccharide (LPS), part of the outer membrane of gram-negative cell walls Has a variety of systemic effects on tissues and organs Causes fever, inflammation, hemorrhage, and diarrhea Blood infections by Salmonella, Shigella, Neisseria meningitidis, and Escherichia coli are particularly dangerous and can lead to shock
- 97. ©McGraw-Hill Education Will Disease Result? ©Dave and Les Jacobs/Kolostock/Blend Images Jump to long description
- 98. ©McGraw-Hill Education Definitions of Infection Types Type of Infection Definition Example Localized infection Microbes enter the body, remain confined to a specific tissue Boils, warts, fungal skin infections Systemic infection Infection spreads to several sites and tissue fluids—usually via the bloodstream—but may travel by other means such as nerves (rabies) and cerebrospinal fluid (meningitis) Mumps, rubella, chickenpox, AIDS, anthrax, typhoid, syphilis Focal infection Infectious agent spreads from a local site and is carried to other tissues Tuberculosis, streptococcal pharyngitis Mixed infection (polymicrobial infection) Several agents establish themselves simultaneously at the infection site Human bite infections, wound infections, gas gangrene Primary infection The initial infection Can be any infection Secondary infection A second infection caused by a different microbe, which complicates a primary infection; often a result of lowered host immune defenses Influenza complicated by pneumonia, common cold complicated by bacterial otitis media Acute infection Infection comes on rapidly, with severe but short- lived effects Influenza Chronic infection Infection that progresses and persists over a long period of time HIV
- 99. ©McGraw-Hill Education Warning Signals of Disease Sign: objective evidence of disease as noted by an observer Symptom: subjective evidence of disease as sensed by the patient Syndrome: a disease identified by a certain complex of signs and symptoms
- 100. ©McGraw-Hill Education Infections That Go Unnoticed No noticeable symptoms are produced Microbe is active in host tissues Host does not seek medical attention These infections are known as asymptomatic, or subclinical (inapparent)
- 101. ©McGraw-Hill Education Steps Involved When a Microbe Causes Disease in a Host Jump to long description
- 102. ©McGraw-Hill Education Long-Term Infections and Long-Term Effects Latency: a dormant state of microbes in certain chronic infectious diseases • Viral latency: herpes simplex, herpes zoster, hepatitis B, AIDS, Epstein-Barr • Bacterial/protozoan latency: syphilis, typhoid fever, tuberculosis, malaria Sequelae: long-term or permanent damage to tissues or organs caused by infectious disease • Meningitis: deafness • Strep throat: rheumatic heart disease • Lyme disease: arthritis • Polio: paralysis
- 103. ©McGraw-Hill Education Stages in the Course of Infection and Disease Jump to long description
- 104. ©McGraw-Hill Education Reservoirs: Where Pathogens Come From Reservoir: • Primary habitat in the natural world from which a pathogen originates • Often a human or animal carrier • Also soil, water, and plants Transmitter: individual or object from which an infection is acquired • Syphilis: reservoir and transmitter are the same • Hepatitis A: reservoir is a human, transmitter is food
- 105. ©McGraw-Hill Education Zoonosis Zoonosis: an infection indigenous to animals but naturally transmissible to humans • Humans are essentially dead-end hosts that do not contribute to the natural persistence of the microbe • Some zoonotic infections have multihost involvement • Some have complex life cycles in the wild • Zoonotic spread of disease is promoted by close associations between humans and animals • Make up a full 70% of all new emerging diseases worldwide • Impossible to eradicate without also eradicating the animal reservoir
- 106. ©McGraw-Hill Education Nonliving Reservoirs Microorganisms have adapted to nearly every habitat in the biosphere: • Thrive in soil, water, air • Surfaces in homes, offices, and other structures in the “built environment” Most are saprobic and cause little harm and considerable benefit Some are opportunists A few are regular pathogens Because humans are in regular contact with environmental sources, acquisition of pathogens from nonliving reservoirs is always a possibility
- 107. ©McGraw-Hill Education Most Common Healthcare-Associated Infections Jump to long description
- 108. ©McGraw-Hill Education Control of HAIs Infection control officer: implements proper practices and procedures, tracks potential outbreaks, identifies breaches in asepsis, and trains health care workers in aseptic techniques Training for nurses and caregivers - regularly exposed to needlesticks, infectious secretions, blood, and physical contact with patients; they need to be especially aware of infection control Most hospitals have adopted universal precautions that recognize that all secretions from all persons in the clinical setting are potentially infectious and that transmission can occur in either direction
- 109. ©McGraw-Hill Education Which Agent Is the Cause? Using Koch’s Postulates Etiologic/causative agent: the cause of infection and disease Koch’s postulates: • A series of proofs that became the standard for determining causation of infectious disease • Continue to play an essential role in modern epidemiology • Reliable for many diseases, but cannot be completely fulfilled in certain situations
- 110. ©McGraw-Hill Education Koch’s Postulates Jump to long description
- 111. ©McGraw-Hill Education Exceptions to Using Koch’s Postulates Some infectious agents cannot be readily isolated or grown in the laboratory Some infections cannot be elicited in animals; viruses have a limited host range, human viruses will only cause disease in humans, etc. Not possible to determine causation in polymicrobial diseases
- 112. ©McGraw-Hill Education Epidemiology: The Study of Disease in Populations Epidemiology: • Study of frequency and distribution of disease and other health-related factors in defined populations • Involves many disciplines: microbiology, anatomy, physiology, immunology, medicine, psychology, sociology, ecology, and statistics • Considers all forms of disease: heart disease, cancer, drug addiction, and mental illness
- 113. ©McGraw-Hill Education Tracking Disease in the Population Reportable or notifiable diseases: • Certain diseases must be reported to authorities • Other diseases are reported on a voluntary basis A network of individuals and agencies at the local, district, state, national, and international levels keeps track of infectious diseases
- 114. ©McGraw-Hill Education Epidemiological Statistics(1) Prevalence: total number of existing cases in a given population; snapshot • Total number of cases in population ÷ total number of persons in population × 100 = % • Example: The prevalence of smoking among adults in the U.S. is 17% currently Incidence: the number of new cases over a certain time period • Number of new cases in a designated time period÷ total number of susceptible persons (usually reported per 100,000 persons): • Example: The incidence of new Lyme disease cases in the U.S. in 2014 was 8.6 per 100,000
- 115. ©McGraw-Hill Education Epidemiological Statistics(2) Statistics of concern to the epidemiologist are rates of disease with regard to sex, race, or geographic region Mortality rate: • Measures the total number of deaths in a population due to a certain disease • Overall death rate from infectious diseases has dropped, although the number of persons afflicted with infectious rates (morbidity rate) has remained high
- 116. ©McGraw-Hill Education Epidemics Common-source epidemic: results from common exposure to a single source of infection over a period of time Propagated epidemic: results from an infectious agent that is communicable from person to person and is sustained over time in a population Point-source epidemic: infectious agent came from a single source, and all of its “victims” were infected at once
- 117. ©McGraw-Hill Education Additional Epidemiology Terms Index case: may not be the first case of the disease, but it is the first case that brought the epidemic to the attention of officials Endemic: an infectious disease that exhibits a relatively steady frequency over a long time period in a particular geographic locale Sporadic: occasional cases are reported at irregular intervals at random locales Epidemic: when statistics indicate that the prevalence of an endemic or sporadic disease is increasing beyond what is expected for a population Pandemic: spread of an epidemic across continents