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: 1. tryptic soy agar (TSA) for E. coli 2. 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

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℃ -10 min, 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

• • • 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℃ -10 min, 60℃ 20 min – Cool down – Streak onto plates – Compare organic matters vs. pure chemical buffer