Microbial Control Terminology

Terminology of Microbial Control

• Sterilization destroys or removes microbial life forms, including vegetative cells, spores, and viruses, from a surface, medium, or article, but not prions.
• Commercial sterilization uses sufficient heat to kill Clostridium botulinum endospores in canned food.
• Antisepsis destroys vegetative pathogens on living tissues.
• Disinfection destroys vegetative pathogens on inanimate objects.
• Decontamination removes pathogenic microorganisms to make an object safe.
• Degerming removes microbes from a limited area, like skin around an injection site.
• Sanitizing/Sanitation lowers bacterial counts to a safe public health level.
• Cleaning physically removes visible soil, dust, or foreign material.
• Sepsis is the presence of microbial contamination, while asepsis is its absence.
• Bacteriostatic agents inhibit bacterial growth and reproduction.
• Bactericidal agents kill bacteria.

Aseptic vs. Clean Techniques

• Aseptic technique aims to eliminate germs entirely.
• Clean technique aims to reduce the number of germs whenever possible.

Rate of Microbial Death

• Bacterial populations die at a constant rate when subjected to heat or antimicrobial chemicals.
• The Microbial Death Curve, plotted logarithmically, shows a constant death rate as a straight line.

Factors Influencing Antimicrobial Agent Effectiveness

• The number of microbes present impacts antimicrobial effectiveness.
• Environmental influences affect antimicrobial action.
• Time of exposure is a factor in antimicrobial efficacy.
• Microbial characteristics influence susceptibility.
• Organic matter presence (blood, feces) affects agent activity.
• The nature of suspending medium affects antimicrobial action.

Actions of Microbial Agents

• Microbial agents can alter membrane permeability.
• Damage to proteins can occur.
• Damage to nucleic acids is a mode of action.

Physical Methods of Microbial Control: Heat

• Heat is a reliable method to destroy microbes.
• Above maximum growth temperature, microbes are killed.
• Below minimum growth temperature, static conditions (inhibition of metabolism) occur.
• Thermal Death Time (TDT) is the minimum time needed to kill a microorganism population at a given temperature and conditions.
• Thermal Death Point (TDP) is the temperature at which a microorganism dies in a given time.
• Decimal Reduction Time (DRT) is the time in minutes to kill 90% of a population.

Moist Heat Sterilization

• Moist heat sterilization breaks hydrogen bonds in bacterial proteins.
• Boiling kills vegetative forms, some viruses, and fungi, but not all microbes, in 10 minutes.
• Autoclaving uses steam under pressure at 15 psi and 121°C for 15 minutes to kill most organisms except prions.
• It kills prions when using 132°C for 4 hours, this being the most dependable sterilization method
• Steam must directly contact materials, avoiding aluminum wrapping.
• Trapped air should not be present.
• Mineral oil/petroleum jelly prevents moisture penetration.
• Pasteurization is another method of moist heat sterilization.

Pasteurization Methods

• Holding Method/Temperature Holding Method (THL) exposes milk at 63°C for 30 minutes, followed by rapid cooling to 13°C.
• Flash Process/High Temperature Short Time (HTST) exposes milk to 72°C for 15 seconds, then cools to 13°C or below.
• Finished product should be stored at low temperatures to retard microorganism growth.
• Ultra-High Temperature (UHT) uses 140°C for 3 seconds.

Dry Heat Sterilization

• Dry heat sterilization kills by oxidation.
• Flaming is a dry heat sterilization method.
• Incineration is a dry heat sterilization method.
• Hot-air sterilization is a dry heat sterilization method.
• Hot air sterilization is the most widely adopted dry heat sterilization using radiating dry heat.
• It requires longer exposure due to poor penetration.
• 160°C is held for 2 hours and it is uses to sterilize glassware, forceps, scissors, scalpels, glass syringes, liquid paraffin, dusting powder.

Filtration

• Filtration is the passage of liquid or gas through pores small enough to retain microorganisms.
• High-efficiency particulate air (HEPA) filters remove microorganisms larger than 0.3 µm.

Low Temperatures

• Ordinary refrigeration (0-7°C) is bacteriostatic, reducing metabolic rate.
• Rapid subfreezing temperatures render microbes dormant, but do not necessarily kill.
• Deep-freezing (-50°C to -90°C) also renders microbes dormant.
• Lyophilization (freeze-drying) quickly freezes from -54°C to -72°C and removes water by high vacuum (sublimation).
• Slow freezing is more harmful to bacteria due to ice crystal formation.

Osmotic Pressure

• High concentrations of salts and sugars are used to preserve food.
• Creates a hypertonic environment causing water to leave the microbial cell.
• Molds and yeasts can grow in low moisture, high osmotic pressure, and acidic environments.

Radiation

• Ionizing radiation has shorter wavelengths and high energy.
• Non-ionizing radiation has longer wavelengths and less energy.

Ionizing Radiation

• Ionizing radiation involves ionization of water, forming reactive hydroxyl radicals.
• It kills organisms by reacting with organic components, especially DNA.
• Nonlethal mutations can occur.

Gamma Rays, X-Rays, and High-Energy Electron Beams

• Cobalt-60 produces Gamma Rays
• Accelerating electrons in special machines produces X-Rays and high-energy electron beams.
• High energy electron beams are used to sterilize pharmaceuticals, disposable dental, medical supplies, and certain postal mail classes.

Non-Ionizing Radiation: Ultraviolet (UV) Light

• UV light at 260 nm is most effective at killing microorganisms.
• It forms thymine dimers, inhibiting DNA replication.
• UV lamps are used in hospitals, clinics, operating rooms, and cafeterias.
• It's used to disinfect vaccines and other medical products.
• It has low penetrating power and can damage human eyes and cause burns/skin cancer.

Visible Light and Sunlight

• Visible light at 470 nm kills methicillin-resistant Staphylococcus aureus.
• Sunlight contains UV radiation but shorter wavelengths are screened out.
• It has antimicrobial effects by forming singlet oxygen in the cytoplasm.
• Bacteria produce pigment to protect them from sunlight.

Microwaves

• Microwaves heat moisture-containing food.
• Heat kills most vegetative pathogens.

Other Methods

• High pressure denatures bacterial proteins and preserves flavor.
• Desiccation inhibits growth but microorganisms can remain viable.

Chemical Methods of Microbial Control

• Few chemical agents achieve sterility.
• Antiseptics are regulated by the FDA.
• Disinfectants are regulated by the EPA.

Mode of Action of Disinfectants

• Disinfectants works by: protein coagulation, cell membrane disruption, removal of free sulfhydryl groups, inhibition of respiration, loss of membrane integrity.
• The Disk Diffusion Method evaluates disinfectant effectiveness.

Phenol and Phenolics

• Phenol (Carbolic acid) was first used by Joseph Lister to control surgical infections.
• It is an antiseptic and disinfectant that irritates the skin.
• Phenolics injure lipid-containing plasma membranes, causing leakage.
• Mycobacteria (TB) are susceptible because their cell wall is rich in lipids.
• Cresol is a phenolic derived from coal tar.
• Bisphenols contain two phenolic groups connected by a bridge, such as Hexachlorophene and Triclosan.
• Triclosan is an ingredient in soaps, toothpastes to inhibit lipid biosynthesis.

Biguanides

• Biguanides affect bacterial cell membranes.
• Effective against gram-positive and gram-negative bacteria (except Pseudomonas).
• Chlorhexidine is used for microbial control on skin and mucous membranes.

Halogens

• Chlorine is an oxidizing agent and disinfectant.
• It forms bleach (HOCl) when added to water.
• It is broad-spectrum but not sporicidal (pools, drinking water).

Calcium Hypochlorite, Sodium Hypochlorite and Chloramines

• Calcium hypochlorite (Ca(OCl)2) disinfects dairy/restaurant utensils.
• Sodium hypochlorite (NaOCl) is a household disinfectant and bleach.
• Chloramines are used to treat drinking water and are more stable.

Iodine

• Iodine is an effective antiseptic.
• It impairs protein synthesis and alters cell membranes.
• Preparations include tincture (iodine in alcohol) and iodophors.
• Povidone-Iodine (Betadine®) is used for skin disinfection and wound treatment.

Alcohol

• Alcohols effectively kill bacteria and fungi, but not endospores or nonenveloped viruses.
• They denature proteins, disrupt membranes, and dissolve lipids.
• Ethyl alcohol (70%) is effective.
• Isopropyl alcohol (rubbing alcohol) is slightly superior as an antiseptic.

Heavy Metals and Their Compounds: Silver

• Silver is used as an antiseptic in 1% silver nitrate.
• Silver-sulfadiazine is a topical cream for burns.
• Surfacine® is antimicrobial for water-insoluble silver iodide surfaces.
• Plastics imbued with silver nanoparticles extend food freshness.
• Silver-infused attire is claimed to minimize odors.
• Silver-impregnated dressings are efficacious versus resistant bacteria.

Heavy Metals: Mercury, Copper, Zinc

• Mercuric chloride (Thimerosal) is bacteriostatic.
• Copper is used as an algicide for water and swimming pools.
• Zinc chloride is an ingredient in mouthwash.

Zinc Pyrithione

• Zinc pyrithione is an ingredient in antidandruff shampoos

Surface-Acting Agents

• Soaps and detergents are degerming agents.
• Acid-anionic sanitizers are used in food-processing facilities.
• Quaternary Ammonium Compounds (Quats) are fungicidal/virucidal.

Chemical Food Preservatives

• Sulfur dioxide (SO2) is a disinfectant in winemaking.
• Sorbic acid and sodium benzoate prevent molds in acidic foods.
• Calcium propionate prevents surface molds in bread.
• Sodium nitrate/nitrite are added to meats; they preserve color and prevent botulism. Nitrites + Amino acids = nitrosamines (carcinogenic).

Aldehydes and Chemical Sterilants

• Aldehydes inactivate proteins by cross-linking.
• Glutaraldehyde sterilizes surgical instruments.
• Formaldehyde inactivates viruses; formalin is a preservative.
• Ethylene oxide denatures proteins and is used for heat-sensitive material.

Plasma Sterilization

• It uses vaporized hydrogen peroxide to sterilize.
• It is effective for heat-sensitive instruments.

Oxidizing Agent: Hydrogen Peroxide

• Hydrogen peroxide is inactivated by catalase.
• It is good for inanimate objects and packaging.
• It acts effectively against anaerobic bacteria.
• Effervescent action aids in wound cleansing.