7. control of microbial growth Flashcards
this is the process by which all living cells, spores and acellular entities (e.g. viruses, viroids and prions) are either destroyed or removed from an object or habitat; it can be accomplished by incineration, non-destructive heat treatment, certain gases, exposure to ionizing radiation, some liquid chemicals, and filtration
sterilization
this is the destruction of pathogenic microorganisms by processes that fail to meet the criteria for sterilization. bacterial spores, organisms with waxy coats (mycobacteria) and some viruses may be resistant; these are agents, usually chemicals that are used only on non-living objects or surfaces
disinfection
this is closely related to disinfection. the microbial population is reduced to levels that are considered safe by public health standards; it is used primarily in housekeeping and food preparation concepts
sanitization
this is the destruction of inhibition of microorganisms on living tissue
antisepsis
these are chemical agents applied to tissue to prevent infection by killing or inhibiting pathogens. they also reduce the total (good and bad) microbial population; they are generally not as toxic as disinfectants
antiseptics
this is the use of chemical agents (antibiotics) to kill or inhibit the growth of microorganisms within host tissue (inside human or animal body)
chemotherapy
substances that KILL microbes have the suffix _____
cide
kills pathogens (and many non-pathogens) but not necessarily endospores
germicide
eliminates spores
sporicide
chemicals that do not kill, but they do prevent the growth of microbes have the suffix _____
static
- preventing infections
- improve surgery and intrusive medical techniques
- food preservation prodcedures
these all apply to the process of __________________
sterilization
what are the different physical methods with regards to heat that can be used to control microbial growth?
- incineration
- dry heat
- moist heat
- pasteurization
- tyndallization
- autoclave
- low temperature
this physical method exposed the surface of the object to direct flame, e.g. flaming wire loops, knife, blade, or needle
incineration
this physical method uses oven heat at 160 degrees C for 2 hours.
- kills vegetative bacteria and spores (sterilization)
- is applicable to metals, glassware, and some heat-resistant oils and waxes
dry heat
this physical method uses boiling/hot water or steam
- reactive water molecules denature proteins in microbes
- kill most of the vegetative bacteria (disinfection)
- bacterial spores can resist boiling for prolonged periods
moist heat
this physical method is the use of heat at a temperature sufficient to kill pathogenic organisms in liquids such as milk, beer, or other food products.
- does not sterilize, but it drastically slows down spoilage by reducing the level of non-pathogenic spoilage microorganisms.
- heating at a temperature of 74 degrees C for 3-5 seconds or 62 degrees C for 30 mins kills the vegetative forms of most pathogenic bacteria
pasteurization
this physical methods is used to destroy heat-resistant micro-organisms
- this process uses steam (30-60 mins) to destroy vegetative bacteria. the steam exposure is repeated for a total of three times with 24 hours incubations between exposures
tyndallization
what is the purpose of the 24 hour incubation periods in tyndallizaiton?
the incubations permit remaining endospores to germinate into heat-sensitive vegetative cells that are destroyed upon subsequent steam exposure
this physical method uses steam under pressure (121 degrees C and 15 psi for 10-15 mins)
- most effective method for sterilization
- kills vegetative cells and spores
autoclave
this physical method inhibits microbial growth and reproduction
- freezing at -20 degrees C or lower stops microbial growth and some microbes will be killed by ice crystals
- freezers (-30 to -80 degrees C) are used in labs for long term storage of microbial samples
- this is a good method for storing food and other items
low temperature/freezing
what are the different physical methods with regards to radiation that can be used to control microbial growth?
- UV light
- ionizing radiation
this physical method uses a 240-280nm wavelength range that causes genetic damage for nucleic acids (forming thymine dimers)
- this type of radiation has poor ability to penetrate glass, water and other substances
- lamps with this type of radiation can be placed on ceilings of rooms to disinfect the air and any other exposed surfaces
UV light
this physical method carries far greater energy than UV and penetrates deep into objects
- causes direct damage to DNA and destroys bacterial endospores and all microbial cells
- cathode and gamma rays from cobalt 60 source are widely used in industrial process, including cold sterilization of antibiotics, hormones, and many disposable surgical supplies such as gloves, plastic syringes, and specimen containers
- can be used to sterilize foodstuffs and meats
ionizing radiation
this physical method is used to sterilize heat-sensitive solutions
- microfilters can be used to remove all microbes (except viruses)
- air can also be sterilized by this method
filtration
