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Microbiology Chapter 9 (test 2)
Controlling Microbial Growth in the Environment
Terms in this set (35)
process of destroying all microbial life on an object.
process of reducing/inhibiting microbial growth on a non-living surface.
process of reducing or inhibiting microorganisms on living tissue.
use of heat to reduce the number of food spoilage organisms. high temperature for a short time (72°C for 15sec.), is used to destroy pathogens without altering the flavor of the food.
Two ways microbial control agents affect a cell
1) alteration of cell walls/permeability 2) damage to proteins/nucleic acids.
Thermal Death Point (TDP)
lowest temperature at which all bacteria in a liquid culture will be killed in 10 minutes.
Thermal Death Time (TDT)
length of time required to kill all bacteria in a liquid culture at a given temperature.
Decimal Reduction Time (DRT)
length of time in which 90% of a bacterial population will be killed at a given temperature.
How does moist heat kill microbes?
121C for 15 min. The most effective method of moist heat sterilization. The steam must directly contact the material to be sterilized.
Ultra-high Temperature (UHT) treatment
(140°C for 3 sec.) is used to sterilize dairy products.
How does dry heat kill microbes?
passage of a liquid or gas through a filter with pores small enough to retain microbes. nitrocellulose or cellulose acetate
Physical Methods of Microbial Control
1) Heat 2) Filtration 3) Low Temperature 4) Desiccation 5) Osmotic Pressure 6) Radiation
Microbes in high concentrations of salts & sugars undergo plasmolysis.
Ionizing, UV types.
How does UV (non-ionizing) radiation affect microbes?
causes cell damage by making thymine dimers in DNA that interfere with DNA replication; the most effective germicidal wavelength is 260nm.
How does ionizing radiation affect microbes?
has a high degree of penetration and exerts its effect primarily by ionizing water and forming highly reactive hydroxyl radicals.
What reduces microbial growth on living tissues?
compounds used to decontaminate nonliving (inanimate) material?
Sterilants, disinfectants, and sanitizers
Minimum Inhibitory Concentration
Antimicrobial activity is measured by determining the smallest amount of agent needed to inhibit the growth of a test organism
bacterial survival in the manufacturer's recommended dilution of a disinfectant is determined
Classes of disinfectants
1) Phenol/Phenolics 2) Alcohols 3) Halogens 4) Oxidizing agents 5) Surfactants 6) Heavy Metals 7) Aldehydes 8) Quaternary Ammonium Compounds (Quats) 9)
Phenolics exert their action by injuring plasma membranes.
Bisphenols such as triclosan (over the counter) and hexachlorophene (prescription) are widely used in household products.
Some halogens (iodine and chlorine) are used alone or as components of inorganic or organic solutions. e.g.: bleach (sodium hypochlorite)A
What is a tincture?
something in solution with alcohol
exert their action by denaturing proteins and dissolving lipids
Exert antimicrobial action through oligodynamic action. When heavy metal ions combine with sulfhydryl (—SH) groups, proteins are denatured
Surface-Active Agents (surfactants)
decrease the tension between molecules that lie on the surface of a liquid; soaps and detergents are examples
Quaternary Ammonium Compounds. Disruption of plasma membranes allows cytoplasmic constituents to leak out of the cell. Quats are most effective against gram-positive bacteria.
Aldehydes such as formaldehyde and glutaraldehyde exert their antimicrobial effect by inactivating proteins.
G- vs G+ resistance to disinfectants/antiseptics
Gram-negative bacteria are generally more resistant than gram-positive bacteria to disinfectants and antiseptics.
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