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Home , Bactericide, Bacteriostatic agent, Boiling

Control of Microbial Growth: Introduction 4 Early civilizations practiced , , Chapter 7: Control of , drying, and exposure of and clothing to sunlight to control microbial growth. Microbial Growth 4 Use of spices in was to mask taste of spoiled food. Some spices prevented spoilage. 4 In mid 1800s Semmelweiss and Lister helped developed aseptic techniques to prevent contamination of surgical wounds. Before then: • Nosocomial caused death in 10% of surgeries. • Up to 25% mothers delivering in hospitals died due to

Control of Microbial Growth: Control of Microbial Growth: Definitions Definitions Sterilization: Killing or removing all forms of Disinfection: Reducing the number of pathogenic microbial life (including endospores) in a material microorganismsto the point where they no longer or an object. cause diseases. Usually involves the removal of vegetative or non-endospore forming pathogens. Heating is the most commonly used method of sterilization. May use physical or chemical methods. Commercial Sterilization: Heat treatment that u : Applied to inanimate objects. kills endospores of Clostridium botulinum the u : Applied to living tissue (antisepsis). causative agent of botulism, in canned food. u Degerming: Mechanical removal of most microbes in a limited area. Example: swab on skin. Does not kill endospores of thermophiles, which u Sanitization: Use of chemical agent on food-handling are not pathogens and may grow at equipment to meet public health standards and minimize above 45oC. chances of disease transmission. E.g: Hot soap & .

Control of Microbial Growth: Control of Microbial Growth: Definitions Definitions Sepsis: Comes from Greek for decay or putrid. : An agent that inhibits the Indicates bacterial contamination. growth of , but does not necessarily kill Asepsis: Absence of significant contamination. them. Suffix stasis: To stop or steady. Aseptic techniques are used to prevent Germicide : An agent that kills certain contamination of surgical instruments, medical micoorganisms. personnel, and the patient during surgery. u : An agent that kills bacteria. Most do not Aseptic techniques are also used to prevent kill endospores. bacterial contamination in food industry. u Viricide: An agent that inactivates viruses. u Fungicide: An agent that kills fungi. u Sporocide: An agent that kills bacterial endospores of fungal spores.

1 Control of Microbial Growth: Control of Microbial Growth: Rate of Microbial Death Rate of Microbial Death When bacterial populations are heated or treated Several factors influence the effectiveness of chemicals, they usually die at a antimicrobial treatment. constant rate. 1. Number of Microbes: The more microbes present, the more time it takes to eliminate population. 2. Type of Microbes: Endospores are very difficult to destroy. Vegetative pathogens vary widely in susceptibility to different methods of microbial control. 3. Environmental influences: Presence of organic material (blood, feces, saliva) tends to inhibit , pH etc. 4. Time of Exposure: Chemical antimicrobials and radiation treatments are more effective at longer times. In heat treatments, longer exposure compensates for lower temperatures.

Phsysical Methods of Microbial Phsysical Methods of Microbial Control: Control: Heat: Kills by denaturing their Moist Heat: Kills microorganisms by coagulating enzymes and other . Heat resistance their proteins. varies widely among microbes. In general, moist heat is much more effective than u Thermal Death Point (TDP): Lowest at dry heat. which all of the microbes in a suspension will be u Boiling: Heat to 100 oC or more at sea level. Kills vegetative killed in ten minutes. forms of bacterial pathogens, almost all viruses, and fungi u Thermal Death Time (TDT): Minimal length of time in and their spores within 10 minutes or less. Endospores and which all bacteria will be killed at a given temperature. some viruses are not destroyed this quickly. However brief u Decimal Time (DRT): Time in minutes at boiling will kill most pathogens. which 90% of bacteria at a given temperature will be u Hepatitis virus: Can survive up to 30 minutes of boiling. killed. Used in canning industry. u Endospores: Can survive up to 20 hours or more of boiling.

Phsysical Methods of Microbial Autoclave: Closed Chamber with High Control: Temperature and Pressure Moist Heat (Continued): Reliable sterilization with moist heat requires temperatures above that of boiling water. u Autoclave: Chamber which is filled with hot under pressure. Preferred method of sterilization, unless material is damaged by heat, moisture, or high pressure. u Temperature of steam reaches 121oC at twice . u Most effective when organisms contact steam directly or are contained in a small volume of liquid. u All organisms and endospores are killed within 15 minutes. u Require more time to reach center of or large volumes of liquid.

2 Phsysical Methods of Microbial Phsysical Methods of Microbial Control: Control: Moist Heat (Continued): Dry Heat: Kills by oxidation effects. u : Developed by Louis Pasteur to prevent the u Direct Flaming: Used to sterilize inoculating loops and spoilage of beverages. Used to reduce microbes responsible needles. Heat metal until it has a red glow. for spoilage of beer, milk, wine, juices, etc. u Incineration: Effective way to sterilize disposable items u Classic Method of Pasteurization: Milk was exposed to 65oC for 30 (paper cups, dressings) and biological waste. minutes. u Hot Air Sterilization: Place objects in an oven. Require 2 u High Temperature Short Time Pasteurization (HTST): Used today. o Milk is exposed to 72oC for 15 seconds. hours at 170 C for sterilization. Dry heat is transfers heat less u Ultra High Temperature Pasteurization (UHT): Milk is treated at effectively to a cool body, than moist heat. 140oC for 3 seconds and then cooled very quickly in a vacuum chamber. Advantage: Milk can be stored at room temperature for several months.

Phsysical Methods of Microbial Phsysical Methods of Microbial Control: Control: Filtration: Removal of microbes by passage of a Low Temperature: Effect depends on microbe and liquid or through a screen like material with small treatment applied. pores. Used to sterilize heat sensitive materials like u : Temperatures from 0 to 7 oC. Bacteriostatic vaccines, enzymes, , and some culture effect. Reduces metabolic rate of most microbes so media. they cannot reproduce or produce toxins. u High Efficiency Particulate Air Filters (HEPA): Used in u Freezing: Temperatures below 0oC. operating rooms and burn units to remove bacteria from air. u Flash Freezing: Does not kill most microbes. u Membrane Filters: Uniform pore size. Used in industry and u Slow Freezing: More harmful because ice crystals disrupt research. Different sizes: cell structure. u 0.22 and 0.45um Pores: Used to filter most bacteria. Don’t retain u Over a third of vegetative bacteria may survive 1 year. spirochetes, mycoplasmasand viruses. u Most parasites are killed by a few days of freezing. u 0.01 um Pores: Retain all viruses and some large proteins.

Phsysical Methods of Microbial Phsysical Methods of Microbial Control: Control: Dessication: In the absence of water, microbes Osmotic Pressure: The use of high concentrations of cannot grow or reproduce, but some may remain salts and sugars in is used to increase the viable for years. After water becomes available, they osmotic pressure and create a hypertonic start growing again. environment. Susceptibility to dessication varies widely: Plasmolysis: As water leaves the cell, u Neisseria gonnorrhea: Only survives about one hour. membrane shrinks away from cell wall. Cell may not u Mycobacterium tuberculosis: May survive several months. die, but usually stops growing. u Viruses are fairly resistant to dessication. u Yeasts and molds: More resistant to high osmotic pressures. u Clostridium spp. and Bacillus spp.: May survive decades. u Staphylococci spp. that live on skin are fairly resistant to high osmotic pressure.

3 Phsysical Methods of Microbial Control: Forms of Radiation Radiation: Three types of radiation kill microbes: 1. Ionizing Radiation: Gamma rays, X rays, electron beams, or higher energy rays. Have short wavelengths (less than 1 nanometer). Dislodge electrons from atoms and form ions. Cause mutations in DNA and produce peroxides. Used to sterilize pharmaceuticals and disposable medical supplies. Food industry is interested in using ionizing radiation. Disadvantages: Penetrates human tissues. May cause genetic mutations in humans.

Phsysical Methods of Microbial Phsysical Methods of Microbial Control: Control: Radiation: Three types of radiation kill microbes: Radiation: Three types of radiation kill microbes: 2. Ultraviolet light (Nonionizing Radiation): 3. Microwave Radiation: Wavelength ranges from 1 Wavelength is longer than 1 nanometer. Damages millimeter to 1 meter. DNA by producing thymine dimers, which cause Heat is absorbed by water molecules. mutations. May kill vegetative cells in moist foods. Used to disinfect operating rooms, nurseries, Bacterial endospores, which do not contain water, are cafeterias. not damaged by microwave radiation. Disadvantages: Damages skin, eyes. Doesn’t Solid foods are unevenly penetrated by microwaves. penetrate paper, glass, and cloth. Trichinosis outbreaks have been associated with pork cooked in microwaves.

Chemical Methods of Microbial Control Chemical Methods of Microbial Control Types of Types of Disinfectants 1. and Phenolics : 2. Halogens: Effective alone or in compounds. u (carbolic ) was first used by Lister as a A. : disinfectant. u u Rarely used today because it is a skin irritant and has strong odor. Tincture of iodine (alcohol solution) was one of first used. u Used in some throat sprays and lozenges. u Acts as local anesthetic. u Combines with amino acid tyrosine in proteins and denatures u Phenolics are chemical derivatives of phenol proteins. u Cresols: Derived from coal tar (). u Stains skin and clothes, somewhat irritating. u Biphenols (pHisoHex): Effective against gram-positive staphylococci u Iodophors: Compounds with iodine that are slow releasing, and streptococci. Used in nurseries. Excessive use in infants may take several minutes to act. Used as skin antiseptic in surgery. cause neurological damage. Not effective against bacterial endospores. u Destroy plasma membranes and denature proteins. u Betadine u Advantages: Stable, persist for long times after applied, and u Isodine remain active in the presence of organic compounds.

4 Chemical Methods of Microbial Control Chemical Methods of Control Types of Disinfectants Types of Disinfectants 2. Halogens: Effective alone or in compounds. 3. : B. : u Kill bacteria, fungi, but not endospores or naked viruses. u When mixed in water forms hypochlorous acid: u Act by denaturing proteins and disrupting cell membranes. Cl + H O ------> H+ + Cl- + HOCl 2 2 u Evaporate, leaving no residue. Hypochlorous acid u Used to mechanically wipe microbes off skin before u Used to disinfect , pools, and sewage. injections or blood drawing. u Chlorine is easily inactivated by organic materials. u Not good for open wounds, because cause proteins to u Sodium (NaOCl): Is active ingredient of coagulate. . u : Drinking alcohol. Optimum concentration is 70%. u Chloramines: Consist of chlorine and . Less effective as germicides. u Isopropanol: Rubbing alcohol. Better disinfectant than ethanol. Also cheaper and less volatile.

Chemical Methods of Control Chemical Methods of Control Types of Disinfectants Types of Disinfectants 4. : 4. Heavy Metals: u Include copper, selenium, mercury, , and zinc. D. Selenium u Oligodynamic action: Very tiny amounts are effective. u Kills fungi and their spores. Used for fungal infections. A. Silver: u Also used in dandruff shampoos. u 1% used to protect infants against gonorrheal E. Zinc eye infections until recently. u Zinc chloride is used in mouthwashes. B. Mercury u Zinc oxide is used as antifungal agent in paints. u Organic mercury compounds like merthiolate and mercurochrome are used to disinfect skin wounds. C. Copper u Copper sulfate is used to kill algae in pools and fish tanks.

Chemical Methods of Control Chemical Methods of Control Types of Disinfectants Types of Disinfectants 5. Quaternary Ammonium Compounds (Quats): 6. Aldehydes: u Widely used surface active agents. u Include some of the most effective antimicrobials. u Cationic (positively charge) detergents. u Inactivate proteins by forming covalent crosslinks with u Effective against gram positive bacteria, less effective several functional groups. against gram-negative bacteria. A. Formaldehyde gas: u Also destroy fungi, amoebas, and enveloped viruses. u Zephiran, Cepacol, also found in our lab spray bottles. u Excellent disinfectant. u Pseudomonas strains that are resistant and can grow in u Commonly used as formalin, a 37% aqueous solution. presence of Quats are a big concern in hospitals. u Formalin was used extensively to preserve biological u Advantages: Strong antimicrobial action, colorless, specimens and inactivate viruses and bacteria in vaccines. odorless, tasteless, stable, and nontoxic. u Irritates mucous membranes, strong odor. u Diasadvantages: Form foam. Organic interferes with u Also used in mortuaries for embalming. effectiveness. Neutralized by soaps and anionic detergents.

5 Chemical Methods of Control Chemical Methods of Control Types of Disinfectants Types of Disinfectants 6. Aldehydes: 7. Gaseous Sterilizers: B. Glutaraldehyde: u Chemicals that sterilize in a chamber similar to an autoclave. u Less irritating and more effective than formaldehyde. u Denature proteins, by replacing functional groups with alkyl u One of the few chemical disinfectants that is a sterilizing groups. agent. A. Ethylene Oxide: u A 2% solution of glutaraldehyde (Cidex) is: u Kills all microbes and endospores, but requires exposure of 4 u Bactericidal, tuberculocidal, and viricidal in 10 minutes. to 18 hours. u Sporicidal in 3 to 10 hours. u Toxic and explosive in pure form. u Commonly used to disinfect hospital instruments. u Highly penetrating. u Also used in mortuaries for embalming. u Most hospitals have ethylene oxide chambers to sterilize mattresses and large equipment.

Chemical Methods of Control Chemical Methods of Control Types of Disinfectants Types of Disinfectants 8. Peroxygens (Oxidizing Agents): 8. Peroxygens (Oxidizing Agents): u Oxidize cellular components of treated microbes. B. Hydrogen Peroxide: u Disrupt membranes and proteins. u Used as an antiseptic. A. : u Not good for open wounds because quickly broken down by u Used along with chlorine to disinfect water. catalase present in human cells. u Helps neutralize unpleasant tastes and odors. u Effective in disinfection of inanimate objects. u More effective killing agent than chlorine, but less stable and u Sporicidal at higher temperatures. more expensive. u Used by food industry and to disinfect contact lenses. u Highly reactive form of . C. Benzoyl Peroxide: u Made by exposing oxygen to electricity or UV light. u Used in .

Chemical Methods of Control Efficiency of Different Chemical Types of Disinfectants Antimicrobial Agents 8. Peroxygens (Oxidizing Agents): D. Peracetic Acid: u One of the most effective liquid sporicides available. u Sterilant : u Kills bacteria and fungi in less than 5 minutes. u Kills endosporesand viruses within 30 minutes. u Used widely in disinfection of food and medical instruments because it does not leave toxic residues.

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