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
