Controlling Microbial Growth Flashcards
Antisepsis
Reduction in the number of microorganisms and viruses in living tissue
Aseptic
Refers to an environment or procedure free of pathogenic contaminents
Cide/Cidal
Kills microbes
Degerming
Removal of microbes by mechanical means (scrubbing)
Disinfection
Destruction of most microorganisms and viruses on nonliving tissue
Pasteurization
Use of heat to destroy pathogens and reduce the number of spoilage microorganisms in foods and beverages
Sanitization
Removal of pathogens from objects to meet public health standards
Stasis/Static
inhibiting growth
Sterilization
Destruction of all microorganisms and viruses on or in an object
Microbial Death: Factors affecting how long it takes to kill bacteria:
- Time of exposure
- environment: slowed by organic matter (feces) and hastened by prior cleaning (heat)
- number of microbes
- characteristics: spores, thick lipid coats, protozoan cysts
Actions of microbial control agents:
- mutations- non-functional proteins
- alterations of membrane permeability- poking holes in membrane causing guts to spill out
- damage to proteins and nucleic acids- if the proteins are damaged, they may not work. some are more critical than others
Physical control methods:
- Temperature: heat preservation (pasteurization), moist heat, dry heat, low heat.
- desiccation- drying out
- osmotic pressure
- radiation
Heat preservation:
must know the temperature and time needed to kill critical bacteria
Thermal Death Time
How long it takes to kill a certain bacteria at a certain temperature
Pasteurization
- used when taste is damaged by longer heat (it lowers the numbers of pathogens 63 degrees for 30 minutes)
- items that are typically pasteurized include milk, juice, ice cream, and yogurt.
- UHT: sterilization (140 degrees for 1-3 seconds) and can cause product to lose some nutritional value
Moist Heat
- denatures proteins
- Boiling: 10 minutes for most pathogens, 30 minutes for hepatitis virus, 20 hours for spores
- Autoclave: uses pressurized steam. 15 psi for 15 minutes at 121 degrees (very penetrating)
Dry Heat
Flaming, oven (170 degrees for 2 hours), spores are resistant to dry heat
Low Temp:
Refrigerator: Bacteriostatic! most pathogens do not grow. Listeria spp. are psychrotolerant. Refrigeration prevents growth
Freezing: slow freezing causes ice crystals. the ice in the membrane can shatter it. Freezing can kill or preserve pathogens
Membrane filtration
Pore size controls which microbes are removed. Using a filter sterilization of 0.2 micrometers will remove all pathogens.
HEPA filters used in safety hoods and operating theaters
Limiting Water
Desiccation: Bacteriostatic! One way to desiccate would be Lyophilization which is used to preserve cultures. You do this by removing all H2O molecules and then when you get to the lab, you add water and then it will grow
Osmotic Pressure
High concentration of salt or sugar. Molds and yeasts are most resistant
Radiation
- Ionizing radiation: gamma rays, x rays, high energy electron beams- (most energy)
- ionization of H2O to form OH- radical
- can cause mutations of DNA and death
Low level and high levels of radiation used for:
Low level ionizing radiation used on spices, some meats, and vegetables.
High energy electron beams used for medical supplies
UV Radiation (Light)
- Causes Thymine dimers in DNA
- Germicidal lamps and vaccine disinfection
- not penetrating
- can damage eyes
Microwaves
Has very little effect on some microbes. Microwaves kill vegetative pathogens by heating. Solid Foods heat unevenly
Chemical Methods:
- Disinfectants/Antiseptics
- Surface-Active agents (Surfactants)
- Chemical food preservatives
- Aldehydes (Formaldehyde= formalin)
- Gas sterilization
- Oxidizing agents
- [antibiotics]
Disinfectants/Antiseptics (Phenols)
- Phenols
- Stable
- Persist for long periods after application
- Active in the presence of organic matter
- Damage lipid membranes
- Example: Dettol
Phenols:
Originally used by Joseph Lister, as carbolic acid vapors during surgery
Disinfectants/Antiseptics (Bisphenol)
- Bisphenols
- Hexachlopophene (pHisoHex) and triclosan
- antibacterial soap and toothpaste
- broad spectrum of activity
Disinfectants/ Antiseptics (Biguanides)
- Biguanides
- Chlorhexidine
- low toxicity
- used on skin and mucous membranes
- surgical scrub used in veterinary hospitals (usually pink)
Disinfectants/Antiseptics (Halogens)
- Halogens
- Iodine: used in solution (Betadine and Isodine)
- Chlorine: gas that forms bleach (hypochlorite) in water. It destroys cell walls and enzymes
Disinfectants/ Antiseptics (Alcohol)
- Alcohol
- Protein denaturation and membrane damage
- Ethanol and Isopropanol most common
- Evaporates very quickly (good and bad)
- 100% alcohol is not good as denaturing proteins requires water molecules
Heavy Metals as Disinfectants:
- Denature proteins
- silver nitrate (topical cream)
- mercuric chloride (paint) used to be used as an antiseptic. it’s poisonous. was used to treat syphilis
- copper sulfate (algicide)
- zinc (mouthwash, paints)
Surfactants
Decrease surface tension, damages lipid membranes, and it’s in soaps (ivory) and detergents.
- Quaternary ammonium compounds: microbicidal
Chemical Food Preservatives
- Sodium benzoate:
- in acidic foods
- reduces pH to 5 or lower which inactivates phosphofructokinase
- Sorbic acid:
- weak acids
- inhibits enzymes
- Calcium propionate
- used in breads to prevent mold
- non-toxic but inhibits growth
- Sodium nitrate/sodium nitrite
- inhibits Clostridium botulinum
- toxic
Aldehydes
- Formaldehyde (formalin) and glutaraldehyde
- used to disinfect instruments
- used to preserve tissues
- irreversibly cross-links protein molecules
Gas Sterilization
- Ethylene oxide
- denatures proteins
- kills all spores and microbes with lengthy exposure
- high penetration
- for use when sensitive to heat or moisture
Oxidizing agents
- benzoyl peroxide
- hydrogen peroxide
- ozone
- peracetic acid (interfere with metabolism, especially obligate anaerobes)
What category does ethylene oxide fall under?
Gas sterilization
What category does phenol fall under?
Disinfectant/antiseptic (it is a disinfectant)
What category does soaps and detergents fall under?
Surfactants
What category does halogens fall under?
Disinfectant/antiseptic (it is an antiseptic)
What category does sodium nitrate and sodium nitrite fall under?
Chemical Food Perservative
What category does formaldehyde fall under?
Aldehyde
What category does hydrogen peroxide fall under?
Oxidizing agent
What category does calcium propionate fall under?
Chemical Food Preservation
What category does biguanide fall under?
Disinfectant/antiseptic
What category does benzoyl peroxide fall under?
Oxidizing agent
What category does sorbic acid fall under?
Chemical Food Preservative
What category does glutaraldehyde fall under?
Aldehyde
What category does ozone fall under?
Oxidizing agent
What category does sodium benzoate fall under?
Chemical Food Preservative
What category does alcohol fall under?
Disinfectant/antiseptic
What category does peracetic acid fall under?
Oxidizing agent
What category does bisphenol fall under?
Disinfectant/antiseptic
What category does silver nitrate, mercuric chloride, copper sulfate and zinc belong to?
Heavy metals as disinfectants
