Controlling microbial growth in the environment Flashcards
What is antisepsis?
Reduction in the number of microorganisms & viruses, particularly potential pathogens, on living tissue
Examples of antisepsis
Iodine & alcohol
Antiseptics are frequently?
Disinfectants whose strength has been reduced to make them safe for living tissues
What is aseptic?
Refers to an environment or procedure free of pathogenic contaminants
Examples of aseptics
Preparation of surgical field; hand washing; flame sterilization of lab equipment
Scientists, lab technicians, & health care workers routinely follow?
Standardized aseptic techniques
What do the terms, cide and cidal mean?
Suffixes indicating destruction of a type of microbe
Examples of cide & cidal
Bactericide, fungicide, germicide, virucide
Germincides include?
Ethylene oxide, propylene oxide, and aldehydes
Define degerming
Removal of microbes by mechanical means (scrubbing, washing hands, nurse preparing an area of skin for an injection)
Examples of degerming
Handwashing; alcohol swabbing at site of injection
Chemicals play a secondary role to the?
Mechanical removal of microbes
Define disinfection
Destruction of most microorganisms and viruses on non-living tissue
Examples of disinfection
Phenolics; alchohols; aldehydes; soaps
The term disinfection is used primarily in relation to?
Pathogens
Define pasteurization
Use of heat to destroy pathogens & reduce the number of spoilage microorganisms in foods & beverages
Examples of pasteurization
Pasteurized milk & fruit juices
Define sanitation
Removal of pathogens from objects to meet public health standards
Examples of sanitation
Washing tableware in scalding water in restaurants
Standards of sanitation vary among?
Governmental jurisdictions
What do, stasis and static mean?
Suffixes indicating inhibition, but not complete destruction, of a type of microbe
Examples of stasis and static
Bacteriostatic, fungistatic, virustatic
Germinstatic agents include?
Some chemicals, refrigeration, and freezing
Define sterilization
Destruction of all microorganisms & viruses in or on an object
Give an example of sterilization
Preparation of microbial culture media & canned food
How is sterilization achieved?
Typically by steam under pressure, incineration, or ethylene oxide gas
Germicides classified as high, intermediate, or low effectiveness depending on their proficiency in inactivating or destroying microorganisms on medical instruments that cannot be sterilized with heat
– High—kill all pathogens, including endospores. Health care professionals use this to sterilize invasive instruments (catheters, implants, parts of heart lung machine)
– Intermediate—kill fungal spores, protozoan cysts,
viruses, pathogenic bacteria. Not endospores. Used to disinfect instruments that come in contact w/mucous membranes but non invasive (respiratory instrument, endoscopes)
– Low—kill vegetative bacteria, fungi, protozoa, some
viruses; used to disinfect items only contact skin (furniture, electrodes)
Germicides classified as high, intermediate, or low effectiveness depending on their proficiency in inactivating or destroying microorganisms on medical instruments that cannot be sterilized with heat
– High—kill all pathogens, including endospores
– Intermediate—kill fungal spores, protozoan cysts,
viruses, pathogenic bacteria
– Low—kill vegetative bacteria, fungi, protozoa, some
viruses
 Why are non-enveloped viruses generally more resistant than enveloped viruses?
A phospholipid envelope is typically more fragile than a protein capsid
Most resistant microbes to most susceptible
Most resistant 1) Prions 2) Bacterial endospores 3) Mycobacteria 4) Cysts of protozoa 5) Active-stage protozoa (trophozoites) 6) Most Gram-negative bacteria 7) Fungi 8) Nonenveloped viruses 9) Most Gram-positive bacteria 10) Enveloped viruses Most susceptible
Effects of high temperatures does what?
– Denature proteins
– Interfere with integrity of cytoplasmic membrane
and cell wall
– Disrupt structure and function of nucleic acids
Moist heat does what?
– Used to disinfect, sanitize, and sterilize
– Denatures proteins and destroys cytoplasmic
membranes
– More effective than dry heat
– Methods of microbial control using moist heat:
* Boiling
* Autoclaving
* Pasteurization
* Ultrahigh-temperature sterilization
Moist heat: Boiling does what?
– Kills vegetative cells of bacteria and fungi, protozoan trophozoites, most viruses
– Boiling time is critical: Different elevations require different boiling times
– Endospores, protozoan cysts, and some viruses can survive boiling
Moist heat: Autoclaving is what?
– Pressure applied to boiling water prevents steamfrom escaping
– Boiling temperature increases as pressure increases
– Autoclave conditions – 121oC, 15 psi, 15 min
Moist heat: Pasteurization is?
– Used for milk, ice cream, yogurt, and fruit juices
– Not sterilization: Heat-tolerant microbes survive
– Pasteurization of milk
– Batch method
– Flash pasteurization
– Ultra high-temperature pasteurization
Dry heat is?
– Used for materials that cannot be sterilized with moist heat
– Denatures proteins and oxidizes metabolic and structural chemicals
– Requires higher temperatures for longer time than moist heat
– Incineration is ultimate means of sterilization
Refrigeration and Freezing does what?
– Decrease microbial metabolism, growth, and reproduction
– Chemical reactions occur more slowly at low temperatures
– Liquid water not available
– Psychrophilic microbes can multiply in
refrigerated foods
– Refrigeration halts growth of most pathogens
– Slow freezing more effective than quick freezing
– Organisms vary in susceptibility to freezing
Physical Methods of Microbial Control: Osmotic Pressure
– High concentrations of salt or sugar in foods
to inhibit growth
– Cells in hypertonic solution of salt or sugar
lose water
– Fungi have greater ability than bacteria to
survive hypertonic environments
Desiccation and Lyophilization is?
– Drying inhibits growth because of removal of
water
– Lyophilization used for long-term preservation of microbial cultures
– Prevents formation of damaging ice crystals
Physical Methods of Microbial Control: OsmoticPressure
– High concentrations of salt or sugar in foods
to inhibit growth
– Cells in hypertonic solution of salt or sugar
lose water
– Fungi have greater ability than bacteria to
survive hypertonic environments
Physical Methods of Microbial Control: Radiation Ionizing radiation
– Wavelengths shorter than 1 nm
– Ejects electrons from atoms to create ions
– Ions disrupt hydrogen bonding, oxidize double
covalent bonds, and create hydroxide ions
– Hydroxide ions denature other molecules (DNA)
– Electron beams – effective at killing but do not penetrate well
– Gamma rays – penetrate well but require hours to kill microbes
Radiation Nonionizing radiation
– Wavelengths greater than 1 nm
– Excites electrons, causing them to make new
covalent bonds
– Affects 3-D structure of proteins and nucleic acids
– UV light causes pyrimidine dimers in DNA
– UV light does not penetrate well
– Suitable for disinfecting air, transparent fluids, and
surfaces of objects
Chemical Methods of Microbial Control: Phenol and Phenolics are?
– Intermediate- to low-level disinfectants
– Denature proteins and disrupt cell membranes
– Effective in presence of organic matter
– Remain active for prolonged time
– Commonly used in health care settings, labs, and homes
– Have disagreeable odor and possible side effects
Chemical Methods of Microbial Control: Alcohols
– Intermediate-level disinfectants
– Denature proteins and disrupt cytoplasmic membranes
– More effective than soap in removing bacteria from hands
– Swabbing of skin with 70% ethanol prior to injection
Chemical Methods of Microbial Control: Halogens
– Intermediate-level antimicrobial chemicals
– Believed to damage enzymes via oxidation or by denaturation
– Widely used in numerous applications
– Iodine tablets, iodophores, chlorine treatment, bleach, chloramines, and bromine disinfection
Chemical Methods of Microbial Control: Oxidizing Agents
– Peroxides, ozone, and peracetic acid
– Kill by oxidation of microbial enzymes
– High-level disinfectants and antiseptics
– Hydrogen peroxide can disinfect and sterilize surfaces
– Not useful for treating open wounds because of catalase activity
– Ozone treatment of drinking water
– Peracetic acid is effective sporocide used to sterilize equipment
Chemical Methods of Microbial Control: Surfactants
– “Surface active” chemicals
– Reduce surface tension of solvents – Soaps and detergents
– Soaps have hydrophilic and hydrophobic ends – Good degerming agents but not antimicrobial
– Detergents are positively charged organic surfactants – Quats
– Low-level disinfectants
– Ideal for many medical and industrial applications
Chemical Methods of Microbial Control: Heavy Metals
– Heavy-metal ions denature proteins
– Low-level bacteriostatic and fungistatic agents
– 1% silver nitrate to prevent blindness caused by
N. gonorrhoeae
– Thimerosal used to preserve vaccines
– Copper controls algal growth
Chemical Methods of Microbial Control: Aldehydes
– Compounds containing terminal –CHO
groups
– Cross-link functional groups to denature proteins and inactivate nucleic acids
– Glutaraldehyde disinfects and sterilizes
– Formalin used in embalming and disinfection
of rooms and instruments
Chemical Methods of Microbial Control: Gaseous Agents–Ethyleneoxide
– Microbicidal and sporicidal gases used in closed chambers to sterilize items – Denature proteins and DNA by cross-linking functional groups – Used in hospitals and dental offices – Disadvantages * Can be hazardous to people * Often highly explosive * Extremely poisonous * Potentially carcinogenic
Factors Affecting the Efficacy of Antimicrobial Methods
– Site to be treated
– Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects
– Microbial control based on site of medical procedure
– Temperature
–pH
– Residual organic matter
The Selection of Microbial Control Methods: Ideally, agents should be?
– Inexpensive
– Fast-acting
– Stable during storage
– Capable of controlling microbial growth while being harmless to humans, animals, and objects
Such ideal products & procedures do not exist- every agent has limitations & disadvantages
Action of Antimicrobial Agents: Damage to proteins and nucleic acids
– Damage to proteins and nucleic acids
– Protein function depends on 3-D shape
– Extreme heat or certain chemicals denature
proteins
– Chemicals, radiation, and heat can alter/destroy
nucleic acids
– Produce fatal mutants
– Halt protein synthesis through action on RNA
Action of Antimicrobial Agents: Alteration of cell walls and membranes
– Alteration of cell walls and membranes
– Cell wall maintains integrity of cell
– When damaged, cells burst because of osmotic
effects
– Cytoplasmic membrane controls passage of
chemicals into and out of cell
– When damaged, cellular contents leak out
– Nonenveloped viruses more tolerant of harsh conditions
What are the factors to consider in selecting a microbial control method?
1) The nature of the sites to be treated
2) The degree of susceptibility of the microbes involved
3) The environmental conditions that pertain
When performing medical procedures, medical personnel must choose a method & level of microbial control based on the site of the procedure, because the site greatly affects the potential for subsequent infection. For example medical instruments…
medical instruments that penetrate outer defenses of the body (needles, scalpels) carry great potential for infection, so they must be sterilized. Disinfection may be used for items that mucous membrane surface contact surface or skin. In the latter case, sterilization is required for immunocompromised
Enveloped viruses (HIV) are susceptible to antimicrobial agents and heat than are?
Non-enveloped viruses (poliovirus) because envelops are more easily disrupted than the protein coats of non enveloped
Bacterial endospores (spores of bacillus) are the most resistant forms of life. They can survive what?
Environmental extremes of temp. & acidity & withstand many chemical disinfectants. They can survive more than 20 yrs in 70% alcohol
Mycobacterium species cell walls contain large amounts of waxy lipids. This wax allows them to?
Survive drying and protects from most water-based chemicals. Must use strong disinfectants or heat to treat whatever comes into contact with TB patients including utensils, equipment and patients room
Cysts of protozoa. A protozoan cyst’s wall prevents?
Entry of most disinfectants, protects against drying, and shields against radiation & heat
