Lecture 14 Flashcards
Name some mechanical physical methods of controlling microorganisms
scrubbing
germicidal soap (alcohol scrubs)
filtration
sedimentation
What is the difference between bland soap and germicidal soap?
bland soap reduces the number of bacteria, but they are still able to multiply. It also lowers the surface tension (emulsifier/surfactant)
germicidal soaps have residual action
What is residual action?
germicidal soap contains a chemical that sticks to skin and continues to work at killing bacteria
Which is better according to the CDC:
non-germicidal (bland) soap OR germicidal soap (alcohol scrubs)?
They are both equals as far as routine hand-washing
the bland soap is best to use if hands are visibly dirty
What is filtration?
Passing a liquid or gas through a membrane filter to remove microorganisms
the filter is made out of cellulose (paper)
Is best for heat labile things
What is a screen hole size of .45 micro meters good for filtering?
Will filter out large prokaryotes and yeast
NOT mycoplasma and other small prokaryotes
What is a screen hole size of .2 micro meters good for filtering?
Will filter out all prokaryotic cells
MISSES viruses
Does a .2 micro meter screen hole sized filter sterilize a solution?
yes, officially
although viruses will still be able to pass through
What is the largest screen hole sized filter which all viruses will be removed?
0.02 micro meters
Why don’t we use 0.01 micro meter screen hole sized filters as the gold standard?
they can easily clog up which prolongs the filtration process
What is sedimentation used for?
water treatment such as the sewer system and septic tanks
What is the mode of action of sedimentation?
suspended particles which eventually settle
What is the process of water treatment?
first sedimentation
then filtration using rocks or soil
finally (in the city ONLY) chlorination
What chemical can be added to increase sedimentation in a septic tank?
ferric sulfate
Name 4 environmental conditions which can be used to control microorganisms
dessication
cold temperatures
osmotic pressure
sunlight
What is dessication? why is it effective against microorganisms?
drying out
it removes water necessary for enzymatic hydrolysis
How long can Hepatitis B survive in a dry environment?
at least 7 days
How long can TB survive in a dry environment?
8 months because of its waxy coat
How long can Syphilis survive in a dry environment?
minutes
How long can Gonorrhea survive in a dry environment?
hours
How long can Salmonella survive in a dry environment?
2 months
How long can spores survive in a dry environment?
indefinetly
How long can E. coli survive in a dry environment?
2 months
How long can HIV AIDS survive in a dry environment?
6 hours outside the body on a dry surface
1.5 days inside cells such as semen and pus
How long can Staphylococcus aureus survive in a dry environment?
2 months
What is the relationship between dessication of microorganisms and the food we eat?
when mixing dry foods (such as cereal) with wet foods (such as milk), eat immediately because bacteria may be static due to dessication and adding liquid will reactivate their growth
Which organism is found in cereals and can become harmful when the cereal gets wet?
Staph aureus
Which organism is found in dried eggs?
Salmonella (of course dummie :P )
Dessication can have an effect on these types of yeast:
________________
athletes foot and yeast infections
they thrive in moist environments
Freezing is cidal to what kinds of organisms? It is NOT cidal to what kinds of organisms
eukaryotic cells
it is NOT cidal to bacteria
What does the freezer do to eukaryotic cells?
frozen water forms crystals which can puncture cell walls
What does the freezer do to bacteria?
it removes the water necessary for enzymatic reactions
the bacterial population does not grow (becomes static)
What does the refrigerator do to bacteria?
slows the rate of enzymatic reaction but does NOT stop it
Bacteria will continue to grow slowly
Name 2 mediums which can be used to control microorganism populations via osmotic pressure
brine and sugar solutions
What happen to bacteria in a hypertonic environment?
they undergo plasmolysis
What grows in brine and is it a problem?
only halophiles will grow but they are non pathogenic
What grows in high sugar solutions and is it a problem?
saccharophilic organisms such as mold will grow in up to 70% sugar solution but they are non pathogenic
What is a high sugar solution used for?
preservation of fruit (would make jams and jellies)
What is the mode of action of sunlight as a form of microorganism control?
photo oxidation (of proteins)
How long can mycobacterium TB last with dessication? with dessication AND sunlight?
8 month in dessication
a few days in the sun
Name different types of radiation
UV Infrared microwaves gamma rays cathode rays x rays
what is the mode of action of radiation?
destroys DNA
Is radiation efffective against prions? why or why not?
no because prions only have RNA
Is UV penetrative?
no
this is why sunblock is effective
What can UV light do to seratia narcescens?
it can be mutated to only be white and never change back to red using laminar flow hoods
Does UV light sterilize or disinfect?
disinfect
Can UV light be used for water purification?
yes
BUT the water has to be very clean to begin with
Does UV light work on spores?
yes
What is the mode of action of UV light?
makes DNA form pyrimidine dimers (cytosine and thymine begin forming bonds with themselves instead of the normal AT and CG bonds) this breaks hydrogen bonds and forms mutations
Are infrared light and microwaves sterilizing or disinfecting?
disinfecting
What can infrared light and microwaves be used on to control microorganisms?
can be used for the disinfection of soft contact lenses and urinary catheters
What is the mode of action of infrared light and microwaves?
non-ionizing
wavelengths get absorbed and given off as heat
if the organism is dry, it is protein oxidation
if it is wet, then it is protein coagulation
Are gamma rays penetrating?
yes, very
except for lead
where do gamma rays come from?
radioactive isotopes such as cobalt 60
what are gamma rays used for? why?
sterilizing bacon and produce
to gain a longer shelf life
do gamma rays deposit radioactive materials in meat?
no
What are cathode rays? What are they used for?
electron beams of high intensity
sterilization of sutures
Do cathode rays sterilize or disinfect?
sterilization of sutures
Are X-rays penetrating?
yes of course
Are X-rays dangerous?
they are too dangerous for routine use
What forms of radiation are ionizing?
gamma rays
cathode rays
x-rays
What is the mode of action of ionizing radiation?
uses ionizing energy to create hyperactive ions
ions strike DNA causing mutation
Can you use ionizing radiation for sterilization or disinfection?
While it could be used for sterilization, the FDA won’t clear a high enough dose due to safety concerns
therefore they are only used for disinfection in the USA
