Control of Microbial Growth Flashcards
Sterilization
The killing or removal of all viable organisms within a growth medium
Inhibition
- Effectively limiting microbial growth
- No killing taking place
Decontamination
The treatment of an object to make it safe to handle
Disinfection
- Directly targets the removal of all pathogens
- Not necessarily all microorganisms
Heat Sterilization
is the most widely used
method of controlling microbial growth
Endospores
Can survive heat that would rapidly kill vegetative cells
Pasteurization
is the process of using precisely controlled heat to
reduce the microbial load in heat-sensitive liquids
- Does not kill all organisms-> not sterilization
Autoclave
The autoclave is a sealed device that uses steam under pressure
- Allows temperature of water to get above 100℃
Radiation
- Physical method of growth control
- Microwaves, UV, X-rays, gamma rays, and electrons can reduce microbial growth
- UV has sufficient energy to cause modifications and breaks in DNA
- UV is useful for decontaminating surfaces
- Cannot penetrate solid, opaque, or light-absorbing surfaces
Ionizing radiation
Electromagnetic radiation that produces ions and other reactive molecules generates electrons, hydroxyl radicals,
and hydride radicals
- Some microorganisms are more resistant to radiation than others.
- amount of energy required to reduce viability tenfold is analogous to D value
Filtration
avoids the use of heat on sensitive liquids and gases
- Pores of filter are too small for organisms to pass through
- Allow liquid or gas to pass through
- Ex) HEPA filters, membrane filters
Membrane Filters
Filtration can be accomplished by:
- Syringe
- Pump
- Vacuum
How can antimicrobial agents be classified?
- Bacteriostatic: prevents cell growth as long as the antimicrobial agent is
present - Bacteriocidal: kills the cells (does not lyse them)
- Bacteriolytic: kills and lyses the cells
Minimum inhibitory concentration (MIC)
- The smallest amount of an agent needed to inhibit
growth of a microorganism - Varies with the organism used, inoculum size,
temperature, pH, etc. - Increasing concentration of antibiotic from left to
right. - Lowest concentration with no growth = MIC
- May still have living (non-growing) organisms
- i.e. the antibiotic may be bacteriostatic
Minimal Lethal Concentration (MLC)
- Plate aliquots of broth from the MIC and from tubes with higher concentrations of antibiotic, on appropriate nutrient agar plates, without antibiotic
- Do colonies form? No colonies = Minimal Lethal Concentration (MLC)
- MLC usually higher than MIC
Disc diffusion assay
- Uses solid media
- Antimicrobial agent is added to filter paper disc
- The MIC is reached at some distance
- Forms a zone of inhibition
- Area of no growth around disc
What the two categories antimicrobial agents can be divided into?
- Products used to control microorganisms in commercial and industrial applications
- Products designed to prevent growth of human pathogens in inanimate
environments and on external body surfaces
Products used to control microorganisms in commercial and industrial applications
Ex) chemicals in foods, air conditioning cooling towers, textile and paper
products, fuel tanks
Products designed to prevent growth of human pathogens in inanimate
environments and on external body surfaces
- Sterilant: destroys all microorganisms including endospores
- Disinfectant: kills microorganisms but not all endospores.
- Used on inanimate objects
- Sanitizer: reduces the numbers of microorganisms on surfaces (e.g. hand
sanitizers) - Antiseptic: kills or inhibits the growth of microorganisms (non-toxic enough to be applied on living tissue (e.g. mouth wash))
