Microbial Control Flashcards
How is osmotic pressure used to inhibit growth?
High concentrations of salt or sugar in foods to inhibit growth
Cells in hypertonic solution of salt or sugar lose water = plasmolysis
Which have a greater ability to survive hypertonic environments? Bacteria or Fungi?
Fungi
What radiation is an alternative to chlorine gas treatment?
UV Radiation
What is more penetrating? Gamma or UV radiation?
Gamma radiation
Which form of radiation is sterilizing? UV or Gamma radiation?
Both are sterilizing
How do you know if food has been gamma irradiated
The radora logo.
What control method uses membranes to remove spores and microbes from the air?
Filtration
When is filtration used?
Liquids that are sensitive to heat (e.g. serum, vaccines, media)
HEPA filtration of operating rooms etc.
What does HEPA stand for?
High Efficiency Particulate Air
Does cold kill microbes?
No. It only reduced their metabolic activity.
Except for psychrophiles.
Stopping microbial metabolism by dehydration.
dessication
Preserving microbes and vaccines by freeze drying.
Lyophilization
Phenol and Phenolics
Examples and uses
Phenol - carbolic acid
- Used by Joseph Lister
- Has bad smell
Phenolic - Lysol
Disrupt plasma membranes
Used in cutting boards, kitty litter
Biguanides
Example and use
Surgical hand scrubs and preoperative skin preparation
disrupt plasma membranes
Ex: Chlorhexidine
- replaced carbolic acid
- No smell
- No skin irritation
- stays on the skin longer
Halogens
Oxidizing agents
Disrupt sulfhydryl groups in amino acids
Iodine
Chlorine
Tincture + Iodine (both antiseptic)
- Idophor - Iodine + proprietary organic base
Organic base allows iodine to stay on longer
Alcohols
Dissolve membrane lipids, denatures proteins.
Used for skin degerming.
Ethanol, Isopropanol
70% concentration - most effective
Soaps and detergents
Quaternary ammonium (quats):
Cationic
Denature proteins and disrupt cell membrane
Low-level disinfectant in the clinical setting
Soaps and detergents:
Fatty acids, oils, sodium or potassium salts
Sanitizing and degerming agents
More effective if mixed with germicides
Heavy Metals
Ag (Silver), Hg (Mercury), Cu (Copper)
Denature proteins
Oligodynamic action
Preservatives in cosmetics and ophthalmic solutions.
Silver nitrate - Ophthalmia neonatorum prophylaxis.
Silver sulfadiazine - burn patients and catheter tips.
Aldehydes
Formaldehyde, Glutaraldehyde
Sterilants for surgical and dialysis instruments
Also formaldehyde is an embalming fluid
Gases
Denature proteins and affect functional groups of DNA.
Sterilizes plastic materials
Example: Ethylene oxide
Peroxygens
Oxidizing agents - form hydroxyl free radicals
Effective against anaerobes
Examples:
H2O2 (Hydrogen Peroxide) - skin and wound cleaner
Peracetic acid - quick method for sterilizing medical equipment
O3 (Ozone) - water treatment
Enzymes
Antimicrobial enzymes act against microorganisms
Human tears contain lysozyme
Digests peptidoglycan cell wall of bacteria
Uses of enzymes to control microbes in the environment
Lysozyme is used to reduce the number of bacteria in cheese
Prionzyme can remove prions on medical instruments
Prionzyme
Enzyme used to remove prions on medical instruments
Food preservatives
Inhibits metabolism
Control molds and bacteria in food and cosmetics
Examples:
Organic acids - sorbic, benzoic, acetic acids
Calcium propionate - bread
Nitrite prevents endospore formation in meat products.
Why is nitrite used in meat products?
Prevents endospore formation
What are the Biosafety Levels?
Four levels of safety in labs dealing with pathogens
Biosafety Level 1 (BSL-1)- Handling microbes that do not cause disease in humans
Biosafety Level 2 (BSL-2)- Handling moderately hazardous agents
Biosafety Level 3 (BSL-3)- All manipulations of microbes done in safety cabinets
Biosafety Level 4 (BSL-4)- Handling microbes that cause severe or fatal disease; Lab
space is isolated, and personnel wear protective suits
How should bleach be used in disinfection?
A 10% solution to kill vegetative bacteria and other microbes (no endospores).
What was silver nitrite used for?
To treat gonorrhea (no longer)
What are the three microbial control methods?
Physical, Chemical, and Mechanical
What are the physical agents used in microbial control?
Heat and Radiation
Types of Heat
Dry - Incineration (Sterilization)
Dry Oven - (Sterilization)
Moist - Steam under pressure (Sterilization)
Boiling Water, Hot Water, Pasteurization ((Disinfection)
Types of Radiation
Ionizing - Gamma, X-Ray, Cathode (Sterilization)
Non-Ionizing - UV (Disinfection)
Types of Chemical Agents
Gases (Sterilization, Disinfection)
Liquids (Animate) - Antisepsis
Inanimate - Disinfection, Sterilzation
Mechanical microbial removal methods
Filtration (Air) - Disinfection
Filtration (Liquids) - Sterilization
Static agents
Inhibit Microbe Growth
Eg: bacteriostatic, fungistatic
-cidal agents
Destroy or kill microbes
Eg; bactericidal, fungicidal
Sterilization
Complete removal or destruction of all viable microbes including endospores
Decontamination
Use of physical or chemical methods to kill vegetative bacterial and other microbes except endospores
Disinfectant
chemical agent used to kill vegetative forms of bacteria and other microbes on non-living surfaces such as wiping off table tops.
Antiseptic
chemical agent used to control microbes on living tissue such as surgical scrubbing of patients
Sanitization
reduction of microbial counts to acceptable levels of public health standards.
Example: Sanitization of eating utensils in restaurants
Degerming
Physical removal or reduction of microbes from a limited area.
Example: Washing of hands with germicidal soap.
Factors affecting efficacy of control methods
Number of microbes
Target microbe characteristics
Environmental factors - temperature, pH, biofilms
Concentration and mode of action of agent
Organic matter - sputum, blood, feces
Ideal antimicrobial control agent
Inexpensive
Fast-acting
Stable during storage
Capable of controlling microbial growth while being harmless to humans, animals, and objects
Modes of action for antimicrobials
Damage to cell wall
Alteration of membrane function
Damage to proteins
Damage to nucleic acids
Damage to cell wall
Blockage of cell wall synthesis
Degradation of cell wall components
Reduction of its stability and integrity
When damaged, effects of osmosis cause cells to burst
Ex: Penicillin, detergents, alcohols
Injury to cell membrane
Bind and penetrate membrane lipids
Loss of selective permeability resulting in leakage of cytoplasmic contents.
Ex: Surfactants – surface active agents.
Effects on Nucleic Acids
Irreversible binding to microbial DNA results in:
Ceasation of transcription and translation
Fatal mutations
Ex: Formaldehyde and ionizing radiation
Effects on proteins
Blockage of enzyme active sites prevents binding of substrate.
Protein denaturation
Protein function depends on 3-D shape
Example: Heat, acids, alcohols, phenolics, and metallic ions.
Boiling
Boiling at 100 ˚C for 10-30 minutes kills most non- spore forming pathogens.
Ex: Boiling of baby bottles and unsafe drinking water
Hepatitis B virus needs at least 1 hour of boiling to be killed.
Pasteurization
Pasteurization reduces spoilage caused by microbes and kills pathogens.
Thermoduric microbes survive
Used in milk industry, wineries, breweries.
Prevents transmission of milk-borne diseases caused by: Salmonella, Campylobacter, Listeria, Mycobacteria.
Pasteurization Methods
Classical (Batch): 63 ˚C for 30 minutes
High Temperature Short Time (Flash): 72 ˚C for 15 seconds
Ultra High Temperature: 140 ˚C for < 1 second
Autoclaving
Uses steam under pressure
Used in media preparation and glassware sterilization
Autoclave setting at 121 ˚C, 15 p.s.i. pressure for at least 15 minutes
effectively destroys spores.
Pressure cooker – a table top autoclave.
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
Hot air oven
Effective at 170˚C for 2 hrs
Useful for sterilization of glasswares and oils
Incineration
destroys microbes to ashes or gas
Bunsen flame - up to 1870˚C
Ex: Sterilization of loops and needles.
Furnace - 800˚C to 6500˚C
Ex: Incineration of animal carcasses.
Ionizing radiation
Ejects orbital electrons from an atom to create ions
Ions create radicals and denature DNA
High energy - penetrates liquids and solids effectively.
Nonionizing radiation
Raises atoms to a higher energy level
Low energy - less penetrating
UV - formation of pyrimidine dimers
Applications of ionizing radiation
Alternative sterilization method
Materials sensitive to heat or chemicals
Some foods (fruits, vegetables, meats)
Applications of Nonionizing radiation
Alternative disinfectant
Germicidal lamp in hospitals, schools, food preparation areas (inanimate objects, air, water)
