Microbial Growth Control

• Everyday activities like washing hands, showering, brushing teeth, refrigerating food, using detergent, disinfectants, and antiseptics help control microbial growth.
• Endospores are the most difficult type of microbe to kill.

Microbial Growth Control

• Sterilization destroys all forms of microbes, eliminating all pathogens.
• Disinfection uses physical or chemical agents to inhibit or destroy microbes on inanimate objects or surfaces, but does not eliminate all pathogens.
• Antisepsis disinfects tissue using a chemical agent safe for human tissue.
• Sanitization reduces pathogens on a surface to meet public health standards.
• Pasteurization uses heat to kill pathogens and reduce spoilage organisms in food and beverages, it's disinfection, not sterilization. Pasteurized milk still spoils.

Factors to Consider for Microbial Control

• Larger numbers of microbes need longer to be killed.
• Control agents needs adequate contact time with microbes to be effective, refer to the label.
• More than one microbe species present will take longer to kill. Endospores and acid-fast bacteria are very difficult to kill.
• Lower temperatures decrease molecular motion, prolonging the time to kill microbes.
• Alkaline environments are harder for microbes to survive in, compared to acidic.
• The presence of substances like blood, saliva, body fluids, and feces decrease agent accessibility and affect control agent effectiveness.
• Prevent endospore formation by killing microbes before they form.

How Microbial Control Agents Kill

• Damage to membrane permeability causes leakage of cellular materials which is needed to sustain life, causing the microbe to burst or shrivel.
• Denaturing proteins, including enzymes, disrupts their 3D shape, impairing function.
• Damage to nucleic acids, specifically DNA and RNA, inhibits DNA replication, transcription, and translation.

Physical Methods of Microbial Control - Heat

• Heat denatures proteins and is applicable, reliable, quick, and cheap.
• Both time and temperature impact the killing of mycobacterium tuberculosis: 30 minutes at 58°C, 2 minutes at 65°C, or 3 seconds at 72°C will kill it.
• Dry heat, like ovens, isn't useful for fluids because it can't penetrate effectively but can act as a sterilant when used correctly.
• Moist heat penetrates more effectively than dry heat.
• Clostridium botulinum needs 120°C for 120 minutes to be killed with dry heat, but moist heat only requires 120°C for 10 minutes.
• Boiling is moist heat, but not reliable for sterilization as protozoan cysts, endospores, and some viruses can survive it.
• Pasteurization uses enough heat to kill pathogens and lower the number of spoilage organisms in food/beverages, but doesn't drastically change flavor. Pasteurization is disinfection.
• The holding method pasteurizes at 62.9°C for 30 minutes, the flash method at 71.6°C for 15 seconds, and the ultra-high temperature method at 140°C for 3 seconds.
• Pasteurization doesn't result in sterilization because pasteurized milk still contains microorganisms that cause spoilage later.
• Autoclaves uses moist heat and pressure to kill all microbes or sterilization through protein denaturation. It runs at 121°C with 15 lbs. of pressure using steam for 15 minutes.
• Cold temperature lowers metabolism, slowering growth and reproduction. Refrigeration slows the growth of most human pathogens, most are mesophiles.
• Drying reduces metabolism, leading to dried beans, peas, fruits, and grains having a longer shelf life.
• Filtration uses filter pores to trap microbes. Examples include masks and HEPA filters.
• Osmotic pressure makes the microbe shrivel or burst. Honey, jams, jellies, and maple syrup have a long shelf life because their hypertonic solutions cause water to draw out of the microbe, which causes it to shrivel and die.
• Radiation damages DNA, gamma rays and X-rays are types of ionizing radiation and can preserve food, vaccines, plastic medical instruments and some medications. UV light is non-ionizing radiation which can be used in operating rooms, morgues, and labs.

Chemical Methods of Microbial Control

• There are 10,000 different chemicals manufactured to control the growth of microbes.
• Check the label about the exact microbes the chemical is effective against.
• Always follow the duration of exposure instructions.
• The presence of organic material like blood, feces, or vomit can decrease accessibility and impact effectiveness.
• Phenol and Phenol Derivatives (Phenolics) alters membrane permeability and denatures proteins. They are effective against some bacteria, viruses, and fungi.
• Dr. Lister used phenol to decrease infection during surgery in 1867.
• Phenol was the first commonly used disinfectant. It has a pungent odor, is expensive, caustic to skin, has solubility, and can damage the central nervous system (a 5-10% solution was generally used). Phenol derivatives called phenolics are used today.
• Phenolics including cresols and bisphenols are found in hard surface disinfectants: pine and clove oil contain natural phenolics, Triclosan (a phenolic) is found in consumer care products.
• Surfactants (Soaps and Detergents) mechanically remove microbes and work against a broad range of microbes.
• Surfactants break up the oils, decreasing surface tension and lifting the microbes off the skin so they can be washed away with water.
• Soaps and detergents have a polar (positive) and non-polar (negative) end. The positive end grabs a negatively charged microbe, while the negative end grabs the positively charged portion of the water.
• Friction, rinsing, and drying is critical to good hand washing, antimicrobial chemicals are often added to soaps, longer exposure durations are usually required for them to be effective.
• Alcohol damages membranes (dissolves lipids) and denatures proteins. It is effective against most bacteria, viruses, and fungi.
• 70% alcohol is best and needs water to be effective. It is used as an antiseptic and a main ingredient in hand sanitizer.
• Alcohol evaporates fast, the duration of exposure can be an issue. Alcohol can also dry the skin out, potentially creating cracks that pathogens can use to enter the body.
• Heavy Metals denature proteins. They are effective against some bacteria, fungi, protozoa, and viruses.
• Silver ointment can treat burn patients and skin infections. Silver can also be incorporated into catheters to prevent urinary tract infections.
• Mercury is a skin antiseptic which is not used in the U.S.. Thimerosal is a mercury-based preservative used in small amounts in anti-venoms, eye solutions, and tattoo ink.
• Zinc is used in mouthwashes and dandruff shampoos.
• Hydrogen Peroxide produces reactive oxygen species (free radicals) that steal electrons from macromolecules to fill their valence shell leading to destruction and can act as an antiseptic, disinfectant, and sterilant.
• Hydrogen peroxide is effective against a broad range of microbes, especially obligate anaerobes, and as a sterilant, if used properly.
• Hydrogen peroxide is most effective against obligate anaerobes because they cannot neutralize it due to a lack of catalase enzyme.
• Obligate aerobes produce catalase to break down hydrogen peroxide. Hydrogen peroxide is effective against obligate aerobes if a significant amount is used during antisepsis because catalase will not be able to completely neutralize it.
• Halogens (Chlorine, Iodine, and Iodophors) denatures proteins and is effective against a broad range of microbes.
• Halogens are ingredients in about 1/3 of all antimicrobial chemicals currently on the market.
• Chlorine contains sodium hypochlorite, and is used in disinfection and antisepsis for over 200 years.
• Iodine and iodophors, where iodophors are iodine and alcohol, don't stain like iodine alone, and are less irritating. Can be used as an antiseptic for pre-op skin prep, surgical scrub, as well as a disinfectant.
• Aldehydes (glutaraldehyde, formalin/formaldehyde, OPA) denature protein and can kill all microbes (sterilant).
• Formaldehyde is a colorless gas with a pungent odor.
• Formalin is a 37% aqueous solution of formaldehyde and water.
• Glutaraldehyde is a chemical relative of formaldehyde and formalin, but is safer, less irritating, and is more effective.
• OPA is similar to glutaraldehyde, but more stable, has less odor, is less irritating, and is faster-acting.
• Aldehydes are used in histology as chemical fixatives for microscope slides, preserving biological specimens, embalming, sterilizing instruments and respiratory therapy or dialysis equipment, also fiber optic endoscopes, and to preserve vaccines.
• Gaseous Sterilizers (Ethylene oxide and Chlorine dioxide) denature proteins and are effective against all microbes (sterilant).
• Ethylene oxide sterilizes heat-sensitive items. These heat sensitive items are disposable syringes, endoscopes, ophthalmic instruments, anesthesia masks, catheters, respirators, surgical staplers/sutures, and artificial heart valves.
• Chlorine dioxide was used after the 9/11 terrorist attacks to treat anthrax dispersed in U.S. buildings. Chlorine dioxide can also be used in water treatment.