UV light
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22 Terms
what are the two main types of radiation used to control microbes?
ionizing radiation and non-ionizing (UV) radiation
what is ionizing radiation?
high-energy radiation (e.g. x-rays, gamma rays) that breaks DNA and kills cells
what does ionizing radiation do to bacteria?
damages dna and cell structures, causing mutations and cell death
what items can ionizing radiation sterilize?
plastic petri dishes, gloves, tubing, medical tools, drugs, food like spices
what is non-ionizing radiation?
weaker radiation, like uv light, that damages dna by forming thymine dimers
what are thymine dimers?
abnormal bonds between dna bases that change dna shape and stop replication
why are thymine dimers bad for bacteria?
they stop proper dna replication, leading to cell death
what kind of dna damage is caused by uv light?
bonding of adjacent thymines (thymine dimers)
what kind of uv is used to kill microbes?
UVC , strongest type of uv light
why must cells be directly exposed to uv light?
UV can’t pass through plastic, glass, or solid objects
which bacteria survive uv better?
spore-forming bacteria
why are endospores resistant to uv light?
their tough coating and dna repair systems protect them
what role does the index card play in the experiment?
it blocks uv to show the difference in bacterial survival
what do you use to measure how well uv killed the bacteria?
compare growth on exposed vs. unexposed (covered) parts of the plate
what kind of medium is used in this uv lab experiment?
TSA
exposure times used in UV experiment
1 minute, 2 minutes, 5 minutes
bacteria used in UV light experiment
B. cereus, Serratia marcesens
Which genus survived the longest exposure to UV?
Bacillus cereus
it’s endospores protected it
the cardboard cover acted as a ____ so we can compare the results of normal bacteria vs UV impacted bacteria
control
if the card were not placed over half the plate, would there be more colonies or fewer?
fewer
UV light would’ve hit all the bacteria and killed more
if you left the plastic lid on the plate, would you expect more colonies or fewer?
more colonies
the UV light can’t pass through plastic, so the lid acts as a shield protecting the bacteria
Serratia marcescens is a ______
fecal coliform