Lecture 6- control of microbial growth Flashcards
what is sterilization?
the killing or removal of all viable organisms within a growth medium
what is inhibition
effectively limiting microbial growth (no killing taking place)
what is decontamination?
treatment of an object to make it safe to handle
what is disinfection?
directly targets the removal of all pathogens but not necessarily all microorganisms
what is the most widely used method of controlling microbial growth?
heat sterilization
how does heat sterilization work?
the high temperature denatures macromolecules
what can heat sterilization not sterilize against?
bacterial endospores because they’re heat resistant
what is the decimal reduction time?
amount of time required to reduce viability tenfold
time it takes for a 10 fold reduction in bacterial numbers
what is pasteurization?
the process of using precisely controlled heat to reduce the microbial load in heat sensitive liquids
does pasteurization sterilize?
NO, it doesnt kill all organisms, thus is not sterilization
what two processes kill coxiella burnetii heat resistant pathogen found in milk?
low temp, long time
-63C for 30 minutes
high temp, short time
-72C for 15 minutes
what is the autoclave?
sealed device that uses steam under pressure
what temperature does the water get to in the autoclave?
above 100C
how does the autoclave ensure sterility?
121C for 15 minutes at 15 pounds per square inch
what is radiation?
physical method of growth control
what is radiation used for?
sterilization in the medical field and food industry (chicken, hamburger, spices…)
what are examples of radiation that can reduce microbial growth?
microwaves
UV
X- rays
electrons
how does UV reduce microbial growth?
has sufficient energy to cause modification and breaks in DNA
what is the UV useful for?
decontaminating surfaces (cannot penetrate solid, opaque or light absorbing surfaces)
what is ionizing radiation?
electromagnetic radiation that produces ions and other reactive molecules. generates electrons, hydroxyl radicals and hydride radicals
what are sources of radiation?
cathode ray tubes
x rays
radioactive nuclides
why might we use filtration to sterilize?
because it avoids the use of heat on sensitive liquids and gases
how does filtration work?
pores of the filter are too small for organisms to pass through so it only allows liquid or gas to pass through
using a membrane filter what are the 3 ways filtration can be accomplished?
syringe
pump
vacuum
what are two different pore sizes the filter can have?
5 micrometer
0.2 micrometer
what filter size is best?
0.2 because it prevents most bacteria from going through
what are 3 ways antimicrobial agents can be classified?
bacteriostatic
bacteriocidal
bacteriolytic
what is bacteriostatic?
prevents cell growth as long as teh antimicrobial agent is present
what is bacteriocidal?
kills the cells (does not lyse them)
what is bacteriolytic?
kills and lyses the cells
what is minimum inhibitory concentration?
smallest amount of an agent needed to inhibit growth of a microorganism
what does it mean that minimum inhibitory concentration varies with the organism used?
size
temp
pH
what does the lowest concentration of MIC exhibit?
no growth but may still have living organisms
if no colonies form on nutrient agar plates what does that mean?
minimal lethal concentration has occurred
what is higher, minimum inhibitory concentration or minimal lethal concentrations?
minimal lethal concentrations
what is a disc diffusion assay? what media is used? what does it form?
-uses solid media
-antimicrobial agent is added to filter paper disc
-minimum inhibitory concentration is reached at some distance
-forms a zone of inhibition
-area of no growth around disc
the antimicrobial agents can be divided into two categories, what are they?
- 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
what is an example of a product used to control microorganisms?
chemicals in foods
air conditioning cooling towers
textile and paper products
fuel tanks
what are the 4 products used to prevent growth?
sterilant
disinfectant
sanitizer
antiseptic
what is a sterilant?
destroys all microorganisms including endospores!
what is a disinfectant?
kills microorganisms but not all endospores
used on inanimate objects
what is a sanitizer?
reduces the numbers of microorganisms on surfaces
ex. hand sanitizers
what is an antiseptic?
kills or inhibits the growth of microorganisms
ex. mouth wash
