Transcript Effecting factors of microorganism growth *radiation (ultraviolet, UV)

Effecting factors of microorganism
growth –radiation (ultraviolet, UV)
chapter 24, page 170
1. Microorganisms:
1.
bacteria: Escherichia coli,
2. Medium:
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2.
tryptic soy agar (TSA) for E. coli
All microorganisms are incubated at 37 ℃ before
experiment.
3. UV light: inside laminar flow hood.
• Procedures
– Each group takes their microbial culture
– Streak the bacterial culture onto TSA plates (two
bacteria on one TSA plate)
– Each group should has 10 TSA
– Separate the plates into 5 groups, each group has
two microorganism (group A, B, C, D, E)
• Turn on the laminar hood
• Place group A plates on test tube racks to get close to the
UV light
• Place group B plates on the bottom surface of the laminar
hood
• Measure distance between the plates and the UV light
• Open the plates
• Pull down the curtain (MUST)
• Turn on UV light
• UV exposure for 10 min
• Turn off UV light
• Close and take plates out
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Place group D plates on the same place of group A
Place group E plates on the same place of group B
Open the plates
Pull down the curtain (MUST)
Turn on UV light
UV exposure for 30 min
Turn off UV light
Close and take out plates
Group C is the control. Do NOT expose group C plates to
UV light.
• Incubate plates 37 ℃ (E. coli and B. subtilis)
• Observe the growth of bacteria on the next day.
• Group on duty on another test
• 畫後再照 (streak, incubate, then UV)
– Streak the bacteria onto one TSA plate in advance
– Place on the positions of A and B (totally two sets)
– UV light for 10 min
– Turn off UV
– Streak on new plates
Effecting factors of microorganism
reduction –heat
• Heat
chapter 24, page 170
– Moisture heat
• Water (water bath) (1-6 group)
• Steam
– Dry heat
• Oven (7-11 group)
• Microorganism
– Non spore producer
– Escherichia coli
Temperature and time
• Temperature
– 80 and 60℃
• Time
– 10 and 20 min
• Heat source
– Water bath (wet heat)
– Oven (dry heat)
• 4 combination
– 80℃ – 10 min, 80℃ -20 min, 60℃ -10min, 60℃ 20 min
– Each treatment has one heat source and one
bacteria
– Each group has 8 plates
– Place the tubes containing bacteria culture into
water bath and oven
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Cool down the tubes with running tap water
Shake the tubes
Streak the bacteria culture onto plates
Incubate plates at 37℃ for 24 hours
Observe on the next day
• Group on duty
– Place the bacterial culture into whole milk instead
of phosphate buffer
– place the tubes into water bath
– 80℃ – 10 min, 80℃ -20 min, 60℃ -10min, 60℃ 20 min
– Cool down
– Streak onto plates
– Compare organic matters vs. pure chemical buffer