Lecture 6: Control of Microbial Growth Flashcards
________: The killing or removal of all viable organisms within a growth medium
sterilization
even endospores!
______: Effectively limiting microbial growth
No killing taking place
inhibition
only acceptable when someone has a functioning immune system, basically just allows your immune system time to “catch up”!
_______: The treatment of an object to make it safe to handle
decontamination
______: Directly targets the removal of all pathogens
Not necessarily all microorganisms
disinfection
is it really true that it kills only pathogens? who knows!
_____ is the most widely used
method of controlling microbial growth
Heat sterilization
why do we use heat sterilization to control microbial growth?
High temperatures denature macromolecules, resistant cells (endospores) can still survive heat
Amount of time required to reduce viability tenfold is called the _______
decimal reduction time
(D)
Time it takes for a 10 fold reduction in bacterial numbers
________: is the process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids
Pasteurization
Does not kill all organisms -> not sterilization!!
when treating milk, how many time and temperature combinations for pasteurization can be used?
many! can use LTLT (low-temp/long-time) ex: 63 C for 30 mins
or HTST (high-temp/short-time) ex: 72 C for 15 secs
why can we use so many different combinations of time/temp for treating milk?
Both processes kill Coxiella burnetii, the causative agent of Q fever, which is
the most heat resistant pathogen found in milk
The ______ is a sealed
device that uses steam under
pressure
autoclave
why do we use liquid (steam) to sterilize using an autoclave?
liquid does a much better job at transferring heat! think of a dry, hot oven vs. boiling water, one transfers heat much more strongly!
what settings is an autoclave typically set to?
121oC for 15 min at 15 pounds per square inch of pressure is
typically used
T/F: To ensure sterility this means that the point that takes the longest to heat must stay at 121
for 15 min
true!
_______: physical method of growth control
radiation
Microwaves, UV, X-rays, gamma rays, and electrons can reduce
microbial growth
why can radiation be used to reduce microbial growth?
UV has sufficient energy to cause modifications and breaks in DNA, used to decontaminate surfaces by killing bugs!
T/F: UV Cannot penetrate solid, opaque, or light-absorbing surfaces
true
_____: Electromagnetic radiation that produces
ions and other reactive molecules generates electrons, hydroxyl radicals,
and hydride radicals
ionizing radiation
T/F: Some microorganisms are more
resistant to radiation than others
true!
T/F: amount of energy (radiation) required to reduce
viability tenfold is analogous to D value
true!
what are three sources of radiation?
cathode ray tubes, X-rays, and radioactive nuclides
_______ is used for sterilization in the medical field and food industry
approved by the WHO and is used in the USA for
decontaminating foods particularly susceptible to microbial contamination
Radiation
hamburger, chicken, spices may all be irridiated
____ avoids the use of heat on sensitive liquids and gases
Filtration!
Pores of filter are too small for organisms to pass through
* Allow liquid or gas to pass through
* Ex) HEPA filters, membrane filters
with the use of membrane filters, filtration can be accomplished by what three devices?
syringe
pump
vacuum
what are the three classifications of antimicrobial agents?
bacteriostatic
bacteriocidal
bacteriolytic
______: prevents cell growth as long as the antimicrobial agent is
present
Bacteriostatic
maintains level and prevents more growth… until drug goes away! still need to give something that will kill all unwanted bugs
_____: kills the cells (does not lyse them)
Bacteriocidal
______: kills and lyses the cells
Bacteriolytic
DNA is released when cells are lysed, other bugs can pick that up and change their phenotype… to our disadvantage!
which antimicrobial agent(s) results in total and viable cell counts being the same?
bacteriostatic and bacteriolytic
which antimicrobial agent(s) results in total and viable cell counts being different?
bacteriocidal
________: The smallest amount of an agent needed to inhibit growth of a microorganism
Minimum inhibitory concentration (MIC)
T/F: the minimum inhibitory concentration is the same in all organisms
false! Varies with the organism used, inoculum size, temperature, pH, etc.
in test tube experiments, the Lowest concentration with no growth = ______
MIC
May still have living (non-growing) organisms
* i.e. the antibiotic may be bacteriostatic
when broth aliquots from MIC are plated on agar plates should colonies form?
yes! MIC should only inhibit the growth of new bacteria, NOT kill
if no colonies form on agar plate from broth aliquots of antibiotics, what is this called?
Minimal Lethal Concentration (MLC)
kills everything! colonies will not form on agar plate
_______:
* 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
Disc diffusion assay
what two categories can antimicrobial agents 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
what are some examples of antimicrobial agents used in commercial and industrial applications?
chemicals in foods, air conditioning cooling towers, textile and paper
products, fuel tanks
not worried about living tissue! can be harsher
what are some examples of antimicrobial agents used for human pathogens?
sterilants, disinfectants, sanitizers, antiseptics
