Ch 9 Micro

Antisepsis

Reduction in the number of microorganisms and viruses, particularly potential pathogens, on living tissue (e.g., iodine or alcohol before an injection)

Antiseptics (relationship to disinfectants)

Frequently disinfectants whose strength has been reduced to make them safe for living tissues

Aseptic

Refers to an environment or procedure free of pathogenic contaminants (e.g., surgical field preparation, hand washing, flame sterilization)

-cide / -cidal

Suffixes indicating destruction of a type of microbe (e.g., bactericide, fungicide, germicide, virucide)

Germicides (examples)

Ethylene oxide, propylene oxide, and aldehydes

Degerming

Removal of microbes by mechanical means (e.g., hand washing, alcohol swabbing at injection site)

Disinfection

Destruction of most microorganisms and viruses on nonliving tissue (e.g., phenolics, alcohols, aldehydes, or soaps on equipment or surfaces)

Pasteurization

Use of heat to destroy pathogens and reduce the number of spoilage microorganisms in foods and beverages

Why pasteurized foods still spoil

Heat treatment is brief to minimize alteration of taste and nutrients, so microbes remain and eventually cause spoilage

Sanitization

Removal of pathogens from objects to meet public health standards (e.g., washing tableware in scalding water in restaurants)

-stasis / -static

Suffixes indicating inhibition but not complete destruction of a type of microbe (e.g., bacteriostatic, fungistatic, virustatic)

Germistatic agents (examples)

Some chemicals, refrigeration, and freezing

Sterilization

Destruction of all microorganisms and viruses in or on an object (e.g., culture media, canned food)

Typical methods of sterilization

Steam under pressure, incineration, or ethylene oxide gas

Microbial death

Permanent loss of reproductive ability under ideal environmental conditions

Microbial death rate

Often constant for a microorganism under a particular set of conditions (a constant percentage of cells die over time)

Antimicrobial action on cell walls and membranes

Damaged cell walls cause cells to burst due to osmotic effects, and damaged cytoplasmic membranes cause cellular contents to leak out

Function of the cell wall

Maintains the integrity of the cell

Function of the cytoplasmic membrane

Contains the cytoplasm and controls passage of chemicals into and out of the cell

Which viruses are more tolerant of harsh conditions?

Non-enveloped viruses

Antimicrobial action on proteins

Extreme heat or certain chemicals denature proteins, and protein function depends on 3-D shape

Antimicrobial action on nucleic acids

Chemicals, radiation, and heat can alter or destroy nucleic acids, producing fatal mutants or halting protein synthesis through action on RNA

Ideal characteristics of a microbial control agent

Inexpensive, fast-acting, stable during storage, and able to control microbial growth while being harmless to humans, animals, and objects

High-level germicides

Kill all pathogens, including endospores

Intermediate-level germicides

Kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria

Low-level germicides

Kill vegetative bacteria, fungi, protozoa, and some viruses

Strategy medical personnel use to select a control method

Choose the method that will kill the most resistant microbes present

Factor affecting efficacy: site to be treated

Harsh chemicals and extreme heat cannot be used on humans, other animals, and fragile objects, so the method depends on the site of the medical procedure

Factor affecting efficacy: temperature and pH

Affect microbial death rates and alter the efficacy of antimicrobial methods

Factor affecting efficacy: organic materials

Interfere with penetration of heat, chemicals, and some radiation, and may inactivate chemical disinfectants

Biosafety Level 1 (BSL-1)

Handling pathogens that do not cause disease in healthy humans

Biosafety Level 2 (BSL-2)

Handling moderately hazardous agents

Biosafety Level 3 (BSL-3)

Handling microbes in safety cabinets

Biosafety Level 4 (BSL-4)

Handling microbes that cause severe or fatal disease (e.g., Ebola virus), requiring full protective suits with air supply

Effects of high temperatures on microbes

Denature proteins, interfere with integrity of the cytoplasmic membrane and cell wall, and disrupt structure and function of nucleic acids

Thermal death point

Lowest temperature that kills all cells in broth in 10 minutes

Thermal death time

Time to sterilize a volume of liquid at a set temperature

Moist heat

Used to disinfect, sanitize, sterilize, and pasteurize, and more effective than dry heat

Methods of moist heat microbial control

Boiling, autoclaving, pasteurization, and ultra-high-temperature sterilization

Boiling (what it kills)

Vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses

Boiling (what survives)

Endospores, protozoan cysts, and some viruses

Why elevation matters for boiling

Different elevations require different boiling times

Autoclaving

Pressure applied to boiling water prevents steam from escaping, raising the boiling temperature as pressure increases

Autoclave conditions

121°C, 15 psi, 15 minutes

Pasteurization (is it sterilization?)

No, heat-tolerant microbes survive

Foods commonly pasteurized

Milk, ice cream, yogurt, and fruit juices

Dry heat

Used for materials that cannot be sterilized with moist heat, and requires higher temperatures for longer time than moist heat

Ultimate means of sterilization

Incineration

Moist heat method that is NOT a common choice (concept check)

Incineration (it is a dry heat method)

Effects of refrigeration and freezing

Decrease microbial metabolism, growth, and reproduction because chemical reactions are slower and liquid water is not available

Refrigeration limitation

Halts growth of most pathogens, but some microbes can multiply in refrigerated foods

Freezing rate and effectiveness

Slow freezing is more effective than quick freezing, and organisms vary in susceptibility to freezing

Desiccation

Drying that inhibits growth due to the removal of water

Lyophilization

Freeze-drying used for long-term preservation of microbial cultures, which prevents formation of damaging ice crystals

Filtration

Physical removal of microbes from liquids or air using filters with pores

HEPA filters

High-efficiency particulate air filters used in biological safety cabinets to remove microbes from air

Osmotic pressure as microbial control

High concentrations of salt or sugar in foods inhibit growth because cells in a hypertonic solution lose water

Which microbes tolerate hypertonic environments better?

Fungi have greater ability than bacteria to survive hypertonic environments

Ionizing radiation

Ejects electrons from atoms to create ions that disrupt hydrogen bonding, oxidize double covalent bonds, create hydroxyl radicals, and denature molecules such as DNA

Electron beams

Effective at killing microbes but do not penetrate well

Gamma rays

Penetrate well but require hours to kill microbes

X-rays

Require a long time to kill microbes, so not practical for microbial control

Non-ionizing radiation

Excited electrons create new covalent bonds, affecting 3-D structure of proteins and nucleic acids

UV light

Causes pyrimidine dimers in DNA, does not penetrate well, and is suitable for disinfecting air, transparent fluids, and surfaces of objects

Chemical agents' targets

Microbes' cell walls, cytoplasmic membranes, proteins, or DNA

Microbes most susceptible to chemical agents

Enveloped viruses and vegetative cells of bacteria, fungi, and protozoa

Phenol and phenolics (mechanism)

Denature proteins and disrupt cell membranes

Phenolics (advantages)

Effective in presence of organic matter and remain active for a prolonged time

Phenolics (disadvantages)

Disagreeable odor and possible side effects

Alcohols (level and mechanism)

Intermediate-level disinfectants that denature proteins and disrupt cytoplasmic membranes

Why 70-90% alcohol beats 100% alcohol

Water is required to denature proteins

Halogens

Intermediate-level antimicrobial chemicals that damage enzymes by denaturation (e.g., iodine tablets, iodophors, chlorine, bleach, chloramines, bromine)

Oxidizing agents

High-level disinfectants and antiseptics that kill by oxidation of microbial enzymes

Hydrogen peroxide limitation

Not useful for treating open wounds due to catalase activity

Ozone use

Treatment of drinking water

Peracetic acid

An effective sporicide used to sterilize equipment

Surfactants

"Surface active" chemicals that reduce surface tension of solvents

Soaps and detergents

Have hydrophilic and hydrophobic ends, and are good de-germing agents but not antimicrobial

Quaternary ammonium compounds (quats)

Low-level disinfectants that disrupt cellular membranes, ideal for many medical and industrial applications

Heavy metals

Ions denature proteins and act as low-level bacteriostatic and fungistatic agents

Heavy metal examples

1% silver nitrate to prevent blindness caused by Neisseria gonorrhoeae, thimerosal to preserve vaccines, and copper to control algal growth

Aldehydes

Denature proteins and inactivate nucleic acids

Glutaraldehyde

Aldehyde that disinfects and sterilizes

Formalin

Aldehyde used in embalming and disinfection of rooms and instruments

Gaseous agents

Gases used in closed chambers to sterilize items by denaturing proteins and DNA, used in hospitals and dental offices

Disadvantages of gaseous agents

Can be hazardous to people, often highly explosive, extremely poisonous, and potentially carcinogenic

Lysozyme

Enzyme in human tears that digests the peptidoglycan cell wall of bacteria, also used to reduce bacteria in cheese

Prionzyme

Enzyme that can remove prions on medical instruments

Considerations for disinfectant use

Age of disinfectant, concentration of disinfectant, and exposure time (NOT brand)

Antimicrobial drugs

Antibiotics, semisynthetic, and synthetic chemicals typically used for treatment of disease, with some used for antimicrobial control outside the body