Chapter 9 - Misha Levish PDF

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Chapter 9 Terminology of microbial control 1. Sterilization  Removal or annihilation of ALL forms of microbial life including viruses and bacterial endospores, EXCEPT prions.  Heating is the most common method of sterilization  Chemical work too 2. Disinfectant  Control directed at destroying only harmful microbes  Mainly vegetative, non-spore forming bacteria  Treat inanimate objects (toilets, desks, kitchen counter tops)  Chemicals most common disinfectant  UV, boiling water, steam, heat alcohol, and bleach to inhibit or destroy microorganism especially pathogens  Disinfection does not guarantee that all pathogens are eliminated; indeed, disinfectants alone cannot inhibit endospores or some viruses. 3. Antiseptic  Chemicals used to treat living tissue  *** swabbing w/alcohol just degerms (moves germs around)***  When a chemical is used on skin or other tissue, the process is called antisepsis and the chemical is called an antiseptic 4. Sanitizer  Chemical or treatment (high temperature) intended to decrease microbial counts to a safe public health level  Minimizes risk of disease transmission  Ex] steam, high-pressure hot water, and scrubbing are used to sanitize restaurant utensils and dishes (treatment)  Ex] chemicals are used to sanitize public toilets  Ex] dish washer sanitizes dishes at home because its heat treated  5. Germicide  Outright kills microbes except endospores Action of antimicrobial agents 1. Damaging cell wall  Expose plasma membrane and make it easier to plasmolyze or burst cells based on water concentration - Ex] Penicillin (- lactam) - Works on Gram+ predominately (only kills the cells that are actively growing and dividing) 2. Damaging Plasma membrane  Allow contents of cell to leak  Usually work by altering lipids or proteins that are in the plasma membrane - Ex] ketoconazole (fungus & yeast) 3. Damage proteins & nucleic acids  Protein: apply heat (or chemical) to denature - Ex] chloramphenicol, erythromycin, streptomycin, tetracycline (all interfere with protein synthesis at 70s ribosome) that will affect mitochondria - These drugs can have serious side effects on the body  Enzymes: stop product formation of enzymes using competitive/non-competitive inhibitors - Ex] sulfa drugs (inhibiting the conversion of PABA into folic acid)  Nucleic Acids: heat, radiation, or chemicals can alter or destroy nucleic acids - Extremely lethal because the cell then can’t make proteins and can’t replicate correctly if it has mutations in the nucleic acid sequence - Physical or chemical agents that interfere with nucleic acids also stop protein synthesis

Physical Methods of microbial control Heat related methods (protein denaturation) 1. Moist heat  Which is commonly used to disinfect, sanitize, sterilize, and pasteurize  Kills cells by denaturing proteins and destroying cytoplasmic membranes  Moist heat is more effective in microbial control than dry heat because water is a better conductor of heat than air 1. Autoclave  Temps to above boiling temp of water (121C)  High pressure (15psi)  15 min is enough to sterilize chemicals and objects that can tolerate moist heat 2. Boiling (boiling point of water is 100C)  Kill off vegetative forms of pathogenic bacteria & most viruses, fungi & fungal spores in 10 minutes  Bacterial endospores and hepatitis viruses can survive 30min- 20hrs of boiling and because of that boiling is not recommended when true sterilization is required  At higher elevations, water boils at lower temperatures because atmospheric pressure is lower  Boiling is effective for sanitizing restaurant tableware or disinfecting baby bottles 3. Tyndallization  Old method of sterilization before autoclaves were invented  Boil water at 100C for 3 days in a row, allowing endospores to germinate and then be killed 2. Dry heat  Kills by oxidation effects (flame loop)  Hot air is an effective sterilizing agent because it denatures proteins and fosters the oxidation of metabolic and structural chemicals  Dry heat requires higher temperatures for longer times than moist heat because dry heat penetrates more slowly  Complete incineration is the ultimate means of sterilization  Sterilized 121C  16hrs - 171C  1hr - 160C  2hrs - Incineration  1500C 3. Pasteurization  Heating of foods to kill off most harmful bacteria  72C for 15 sec for milk  Partial sterilization Freezing  Refrigeration slows & halts growth not kill  Slow freezing, during which ice crystals have time to form and puncture cell membranes, is more effective than quick freezing in inhibiting microbial metabolism  psychrophilic (cold-loving) microbes can still multiply in refrigerated food and spoil its taste and suitability for consumption.  many vegetative bacterial cells, bacterial endospores, and viruses can survive subfreezing temperatures for years Filtration  Passage of a liquid or gas through a screen like material with pores small enough to retain the microbes.  HEPA (High Efficiency Particular Air): filters and removes most microbes from the air  Required in 2 sections of the hospital (surgical & burn unit)  Sterilize heat sensitive materials  Ex] media, vaccines, certain antibiotics (liquid form)

Physical Methods of microbial control continued… Radicals steal electrons and Radiation causes a chain reaction 1. Ionizing (more harmful than UV)  Use for food, pharmaceuticals, disposal medical/dental equipment  Ionize water and form hydroxy radicals (which is a toxic form of oxygen) that interact w/DNA and break it apart  X-rays, electron beams, and gamma-rays have a wavelength less than 1nm (short wavelengths)  Ex] x-rays: radioactive elements  Ex] electron beams  Electron beams are highly energetic and therefore very effective in killing microbes in just a few seconds, but they cannot sterilize thick objects or objects coated with large amounts of organic matter  Ex] gamma- rays: radio active elements  penetrate much farther than electron beams but require hours to kill microbes  Irradiation with gamma rays kills not only microbes but also the larvae and eggs of insects  it also kills the cells of fruits and vegetables, preventing both microbial spoilage and overripening 2. UV (skin cancer)  Has a longer wavelength than ionizing  Damages DNA by formation of thymine dimers (thymine is a nucleotide)  Used to sterilize vaccines  UV light has sufficient energy to be a practical antimicrobial agent  UV light is therefore suitable primarily for disinfecting air, transparent fluids, and the surfaces of objects, such as barber’s shears and operating tables Chemical methods of microbial control 1. Phenolics  Lister was the first to use  Ex] cresol, Lysol  Disrupts plasma membranes and denatures enzymes  Stable for long periods after application  Paces used: environmental surfaces, medical instruments, skin surfaces, mucus membranes (mouth wash)  Ex] o-Phenyl Phenol: specifically attacks mycobacterium lipid containing membranes (TB)  Negative aspects of phenolics include their disagreeable odor and possible side effects; for example, phenolics irritate the skin of some individuals. 2. Alcohols  Works by denaturing proteins and lipid dissolution  are bactericidal, fungicidal, and viricidal against enveloped viruses; however, they are not effective against fungal spores or bacterial endospores  commonly used alcohols include rubbing alcohol (isopropanol) and drinking alcohol (ethanol)  Used for thermometers and instruments  Isopropanol is slightly superior to ethanol as a disinfectant and antiseptic  solutions of 70% to 90% alcohol are typically used to control microbes  Swabbing the skin with alcohol prior to an injection removes more microbes by physical action (degerming) than by chemical action 3. Halogens  Group 17 on periodic table are great for controlling microbial growth  Strong oxidizers (they are going to steal electrons and destroy DNA and proteins)  are intermediate-level antimicrobial chemicals that are effective against vegetative bacterial and fungal cells, fungal spores, some bacterial endospores and protozoan cysts, and many viruses  Halogens exert their antimicrobial effect by unfolding and thereby denaturing essential proteins, including enzymes.  Iodine: antiseptic; works by inhibits protein function  Chlorine: hypochlorous acid (extremely strong oxidizer that alters cell components)   Cl

C l2 (chlorine gas)→ H 2 O treatment O 2 → chlorine dioxide for dairy equip

 Chlonine Compounds (bleach)  silverware, glassware & household items

4. Oxidizing agents  High level disinfectants and antiseptics  Work by releasing toxic O 2 forms (radicals)  Particularly effective against anaerobic bacteria b/c they don’t have the enzymes to neutralize the toxic oxygen  Ex] hydrogen peroxide

H (¿ ¿ 2 O2) ¿

is a good disinfectant for medical equipment

 does not make a good antiseptic for open wounds because catalase—an enzyme released from damaged human cells—quickly neutralizes hydrogen peroxide by breaking it down into water and oxygen gas, which can be seen as escaping bubbles  Ex] Ozone ( O 3 ¿ some countries use for water treatment instead of chlorine  Ozone gives air its “fresh smell” after a thunderstorm  Ozone is a more effective antimicrobial agent than chlorine, but it is more expensive, and it is more difficult to maintain an effective concentration of ozone in water. 5. Surfactants (soap made of ammonium)  Surface active chemicals  Ammonium based  Cationic detergents (positive charge)  They inhibit enzymes and denature proteins (damage plasma membrane)  Bactericidal, fungicidal, viricidal (against enveloped viruses)  Ex] soap, cepacol, zephiran  Antiseptics for skin, instruments, utensils, rubber goods  Two common surfactants involved in microbial control are soaps and detergents.  soaps by themselves are good degerming agents though poor antimicrobial agents  when household soaps are antiseptic, it is largely because they contain antimicrobial chemicals. 6. Heavy metals (great for killing off bacteria)  works by denaturing our enzymes and proteins  Mercury (Hg) is biocidal (anything that is alive mercury will kill)  Silver (Ag) is biocidal  Ag (N O 3 ¿ 2 (silver nitrate)  used to treat neonatal gonorrheal opthalimin  Copper sulfate (

C u2 S O 4 ¿  algicide for lakes or streams (kills algae)

 Toxic at low concentrations 7. Aldehydes  Protein denaturation  Very effective anti-microbials  Glutaraldehyde (cidex) is less irritating than formaldehyde  Bacteriocidal, tuberculocidal, virucidal  10min, sporicidal 3-10hrs  Embalming agents  Glutaraldehyde, which is a liquid, and formaldehyde, which is a gas, are highly reactive chemicals  Aldehydes function in microbial control by cross-linking organic functional groups, including amino, hydroxyl, sulfhydryl, and carboxyl thereby denaturing proteins and inactivating nucleic acids.  Hospital personnel and scientists can use 2% solutions of glutaraldehyde to kill bacteria, viruses, and fungi; a 10-minute treatment effectively disinfects most objects  Morticians and health care workers use formaldehyde dissolved in water to make a 37% solution called formalin  They use formalin for embalming and to disinfect hospital rooms, instruments, and machines. 8. Gases  Ethylene oxide forms radicals in AA side-groups  kills all life in several hrs  toxic & explosive in pure form, so mix w/CO2 to make stable  Chlorine dioxide o Made were used o Used to fumigate for anthrax o Stable in aqueous solutions, so used for H2O treatment  Many items can be sterilized within a closed chamber containing highly reactive microbicidal and sporicidal gases such as ethylene oxide propylene oxide and beta propiolactone

Antisepsis: reduction in the number of microorganisms and viruses, particularly potential pathogens, on living tissue  Ex] use of iodine or alcohol to prepare the skin for an injection Aseptic: describes the condition of being without contamination by pathogens.  Ex] preparation of surgical field, handwashing, flame sterilization, of laboratory equipment -cide/cidal: indicating destruction of a type of microbe  Ex] bactericide, fungicide, germicide, virucide Degerming: the removal of microbes from a surface by scrubbing  Ex] handwashing, alcohol swabbing at the injection site -stasis/static: indicating inhibition but not complete destruction of a type of microbe  Ex] bacteriostatic, fungistatic, virustatic...