Ch 7: Control of Microbial Growth Flashcards
What is the difference between disinfection and antisepsis?
Disinfection: treatment used to kill or inhibit microorganisms on inanimate objections
Antisepsis: treatment used to kill or inhibit organisms on living tissue
What is degerming?
Removing microbes from a limited area
What is sanitization?
Lower microbial counts on eating utensils
What is sepsis?
Presence of a toxin or pathogenic organism in blood and tissue
What is Asepsis?
Absence of contamination by unwanted bacteria
What factors influence the effectiveness of antimicrobial treatments?
- Number of microbes
- environmental influences
- time of exposure
- Microbial characterists
What type of environmental influences can influence the effectiveness of antimicrobial treatments?
- Presence of organic matter that protects from antimicrobials (i.e. biofilm)
- Suspensions rich in fats and proteins that protect from heat
- Temperature
What is the thermal death point (TDP) of a microbe?
THe lowest temperature at which all the microbes in a liquid culture will be killed in 10 minutes
What is the thermal death time (TDT) of a microbe?
The length of time required to kill all microbes in a liquid culture at a given temperature
What is the decimal reduction time (DRT or D value) of a microbe?
The length of time required to kill 90% of a bacterial population at a given temperature
How effective is boiling at killing microbes?
100 ℃ kills all vegetative bacterial pathogens, fungi and their spores, and most viruses within 10 minutes
EXCEPT ENDOSPORES
How does autoclaving work?
Sterilization by steam under pressure of about 15 psi (121 ℃)
Kill all organisms and endospores in about 15 minutes
What is pasteurization?
Eliminates pathogens and reduces food spoilage organisms without alter flavor of food
What is Vat pasteurization?
Pasteur’s original method
Heat 63 ℃ for 30 minutes
How is milk most commonly pasteurized today?
High-temperature short-time (HTST)
72 ℃ for 15 seconds
Why do pasteurization times and temperatures vary for different food products?
- Heat is less efficient in viscous foods
- Fats in foods are protective against heat
How does the dairy industry routinely measure the effectiveness of pasteurization?
Phosphatase assay (normal milk enzyme denatured in pasteurization)
How is milk sterilized?
Ultra-high-temperature: 140 ℃ for 2-5 seconds
What are some dry heat sterilization methods?
- Hot-air sterilization
- Direct flaming to a red glow
- Incineration
How does membrane filtration work?
Liquid is passed through a membrane (cellulose acetate, nitrocellulose, etc.) to remove microbes >0.22 μm (some can filter 0.01 μm)
High-efficiency particulate air (HEPA) filter remove microbes _____
>0.3 μm
In what situation is filtration the only practical way to eliminate undesirable microbes?
If you have something you don’t want destroyed by the heat of an autoclave
Refrigeration (0-7 ℃) is _____ for most microbes aside from psychotrophs.
Bacteriostatic
Deep-freezing renders microorganisms _____
Dormant
Does not necessarily kill them
What very high pressure is applied to a liquid suspension to kill microbes? How does it compare to pressures in the deepest parts of the ocean?
87,000 psi for 3-5 mins
Ocean: 16,000 psi
What is desiccation?
Halting of metabolism by extreme dehydration, however it leaves cells viable for years
How does ionizing radiation kill microbes? Examples?
Splits water into ROS that react with cell components (especially DNA)
Ex: X-rays, gamma rays, high energy electron beams
How does nonionizing radiation kill microbes? What wavelength is most effective?
Induces thymine dimers
UV, 260 nm
How do microwaves kill microbes?
Moisture heating
What does this symbol indicate?
Food that has been irradiated
Would a UV germicidal lamp be a good method for a post office to sterilize mail?
No. Can’t penetrate paper
What type of radiation is used to sterilize disposable dental and medical supplies?
Gamma and high energy electron radiation
What factors must be considered when disinfecting?
- Disinfectant concentration
- Contact with microbe (is scrubbing necessary?)
- Time
- Nature of disinfected medium (pH or presence of organic material)
True or false. No single disinfectant is appropriate for all conditions.
True
What is the Use-Dilution test?
The current standard for evaluating the effectiveness of disinfectants and antiseptics
Dried cultures are placed in the manufacturer’s recommended dilution of a disinfectant for 10 minutes at 20 ℃. Survival is demonstrated by turbidity (culture)
What is the disk-diffusion method for evaluating the effectiveness of disinfectants and antiseptics?
A disk of filter paper is soaked with a chemical and placed on an inoculated agar plate, a clear zone of inhibition indicates effectiveness
Why is phenol no longer used as a disinfectant?
Skin irritation and disagreeable odor
What are phenolics? Examples?
Phenol derivatives designed to reduce irritating qualities and increase antimicrobial activity
Ex: O-phenylphenol (active ingredient in lysol)
What are bisphenols?
Disinfectants that contain two phenolic groups covalently linked
What is hexachlorophene?
Bisphenol used in prescription skin cleanser pHisoHex for acne, surgical soap, and nursery infections
What is Triclosan?
Bisphenol that was until recently used as an antimicrobial in soap, mouth wash, toys, underwear, sponges, etc.
What law is in place in regard to triclosan?
Cannot be in anything non-medical due to concerns that bacteria may develop a resistance to it
How do phenols, phenolics, and bisphenols act as antimicrobials? What microbe is especially susceptible to them?
Disrupt plasma membrane
Mycobacteria most susceptible
What are biguanides? Example?
Disinfectants synthesized from guanine that act on the cell membrane
Ex: chlorohexidine
What are biguanides least effective against?
Nonenveloped viruses and spores
What halogens can be used as disinfectants?
Iodine (I2) as betadine
Chlorine (Cl2) as hypochlorous acid or bleach
How does alcohol work as a disinfectant?
Denaturing proteins and dissolving lipid bilayers
What heavy metals can be used as disinfectants?
Silver
Mercury
Copper
Zinc
How do heavy metals work as disinfectants?
Proteins are denatured when heavy metal ions combined with sulfhydryl (-SH) groups
How do sodium benzoate and potassium sorbate function as food preservatives?
Bacteriostatic and fungistatic respectively in acid foods (cheese and soft drinks)
How does calcium propionate function as a food preservative?
Preservative for bakery products. Active against bread molds and spores
How does sulfur dioxide function as a food preservative?
Inhibit microbial growth in wine and dried fruit
How do sodium nitrates and nitrites function as food preservatives?
Selectively inhibit iron-containing enzymes of C. botulinum in meats
What antibiotics are used in food preservation? (2)
Natamycin: against molds and yeasts in cheeses
Nisin: against gram-positive organisms and spores in cheeses
What organism produces natamycin?
bacterium Streptomyces natalensis
What organism produces nisin?
Bacterium Lactococcus lactis
What are the most effective chemical disinfectants?
Aldehydes
How do aldehydes act as disinfectants?
Inactivate proteins by cross-linking with function groups:
- NH2
- OH
- COOH
- SH
What are the 3 most effective aldehydes used for disinfection?
- formaldehyde
- Gluteraldehyde
- ortho-phthaladehyde
What are the two most commonly used gaseous chemo-sterilants?
Ethylene oxide
Chlorine dioxide
How does plasma sterilization work?
Hydrogen peroxide vapor is ionized by an electrochemical field to produce UV light and free radicals (ROS)
Are gram-negative or gram-positive bacteria more resistant to disinfectants and antiseptics?
Gram-negative
True or false. Mycobacteria, endospores, and protozoan cysts are susceptible to disinfectants and antiseptics.
False. They are very resistant
