CHAPTER 6 Flashcards
Antimicrobial agent
Anything that kills (cidal) or inhibits the growth of (static) microbes
Aseptic
Environment that is free of contamination
Sterilization
destruction of all microorganisms and viruses in or on an object
Sterile
any object that has been subjected to sterilization.
Disinfection
Involves the use of physical or chemical agents known as disinfectants, that inhibit or destroy vegetative microbes (not endospores) and many viruses on inanimate objects
Disinfectant
Involves the use of physical or chemical agents known as disinfectants, that inhibit or destroy vegetative microbes (not endospores) and many viruses on inanimate objects
Antisepsis
Reduction in the number of microorganisms and viruses, particularly potential pathogens on living tissues.
Antiseptic
inhibit or destroy vegetative microbes (not endospores) and many viruses on living tissue
degerming
Removal of microbes by mechanical means
sanitization
Removal of pathogens from objects to meet public health standards
pasteurization
use of heat to destroy pathogens and reduce the number of spoilage microorganisms in foods and beverages
-static and -cidal
static- inhibition
cidal- destroy kill
Microbial death
The permanent loss of reproducibility under ideal environmental conditions.
Microbial death rate
The number of bacteria that die over a given period.
Germicide Classification
Relative susceptibility of microorganisms
High Level
Kill all pathogens, including endospores
Intermediate Level
kill fungal spores, protozoan cyst, viruses, and pathogenic bacteria
Low Level
Kill vegetative bacteria, fungi, protozoa, and some viruses
Biosafety level
Four levels of safety in labs dealing with pathogens
• 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
Heat-Related Methods
Effects of high temperatures:
Denature proteins
Interfere with the integrity of the cytoplasmic membrane and cell wall
Disrupt structure and function of nucleic acids
thermal death point
The lowest temperature that kills all cells in broth in 10 minutes
thermal death time
Time to sterilize volume of liquid at set temperature
decimal reduction time (D)
The number of minutes it takes for a defined temperature to reduce the number of viable bacteria in a sample by 90%
Moist heat
Used to disinfect, sanitize, sterilize, and pasteurize
Denatures proteins and destroys cytoplasmic membranes
More effective than dry heat
Methods of microbial control using moist heat:
Boiling
Autoclaving
Pasteurization
Ultra-high temperature sterilization
Boiling
Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses
• Boiling time is critical
• Different elevations require different boiling times
• Endospores, protozoan cysts, and some viruses can survive
boiling
Autoclave
Pressure applied to boiling water prevents steam from escaping
• Boiling temperature increases as pressure increases
• Autoclave conditions: 121°C, 15 psi, 15 minutes
Pasteurization
Used for milk, ice cream, yogurt, and fruit juices • Not sterilization
• Heat-tolerant and heat-loving microbes survive
ultra-high-temperature sterilization
140°C for 1 to 3 seconds, then rapid cooling
• Treated liquids can be stored at room temperature
Dry heat
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
Desiccation
Desiccation (drying) inhibits growth due to the removal of water
Lyophilization
(freeze-drying) is used for the long-term preservation of microbial cultures. Prevents the formation of damaging ice crystals
Filtration
Fluids are forced through a filter that traps any microbes that may be present
Commonly used for media that cannot be autoclave sterilized
Filter size dictates what is allowed through
Bio safety cabinet
type of biocontainment equipment used in biological laboratories to provide personnel, environmental, and product protection.
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
Ionizing radiation
Wavelengths shorter than 1 nm (examples: electron
beams, gamma rays, some X rays) can cause molecules to ionize
What are ions and what effect might they have on microbes?
Electron beams effective at killing microbes but do not penetrate well
Gamma rays penetrate well but require hours to kill microbes, X rays require long time to kill microbes
Not practical for microbial control
non-ionizing radiation
Wavelengths greater than 1 nm (example: UV light) excites electrons, but does not form ions
▪ 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
Phenols and phenolics
Denature proteins and disrupt cell membranes Effective in presence of organic matter
Remain active for prolonged time
Commonly used in health care settings and labs Have disagreeable odor and possible side effects
Alcohols
Intermediate-level disinfectants
Denature proteins and disrupt cytoplasmic membranes
More effective than soap in removing bacteria from hands
Swabbing of skin with alcohol prior to injection removes most microbes Not effective against fungal spores or bacterial endospores
Examples: ethanol, isopropanol, methanol
Halogens
Intermediate-level antimicrobial chemicals Damage enzymes by denaturation
▪ Chlorine ▪ Iodine
Oxidizing agents
High-level disinfectants and antiseptics Peroxides, ozone, and peracetic acid
Kill by oxidation of microbial enzymes
Hydrogen peroxide can disinfect and sterilize surfaces
Not useful for treating open wounds due to catalase activity Ozone treatment of drinking water and air
Peracetic acid is an effective sporicide used to sterilize equipment
▪ Hydrogen peroxide ▪ Ozone (O3)
Surfactants
Surface active” chemicals. Reduce surface tension of solvents
Soaps - have hydrophilic and hydrophobic ends
• Good degerming agents but not antimicrobial
Detergents- Detergents are positively charged organic surfactants
Heavy metals
Low-level bacteriostatic and fungistatic agents Heavy-metal ions denature proteins
1% silver nitrate once used to prevent blindness caused by Neisseria gonorrhoeae
Thimerosal used to preserve vaccines
Silver, zinc, mercury, lead, arsenic, etc.
Aldehydes
cross-link functional groups to denature proteins and inactivate nucleic acids
Formaldehyde - Formalin is used in embalming and disinfection of rooms and instruments
Glutaraldehyde- Glutaraldehyde disinfects and sterilizes
Enzymes
Antimicrobial enzymes act against microorganisms Human tears, saliva, and breast milk contain lysozyme Digests peptidoglycan cell wall of bacteria
▪ Lysozymes- Digests peptidoglycan cell wall of bacteria
▪ Prionzymes- Prionzyme can remove prions on medical instruments
Antimicrobial drugs
Antibiotics, semisynthetic, and synthetic chemicals
Typically used for the treatment of disease
Some used for antimicrobial control outside the body
Anything that kills (-cidal) or inhibits the growth of (-static) microbes is an?
Antimicrobial
What are the three classes of antimicrobial agents?
1.Physical agents
2. Chemical agents
3. Chemotherapeutic
An environment that is free of contamination is called?
Aseptic
Procedures taken to maintain an environment that is free of contamination are called?
Sterilization