MCB 2010L – Microbiology
Water Disinfection, UV Light, and Evaluation of Antiseptics
Disinfection of Drinking Water – Lab 23
Work with entire bench (6 students)
o There will be 6 petri dishes, one for each student
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Perform step 1
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Plate 1 – label “control – bleach”
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Plate 2 – label “control iodine”
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Perform step 2
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Plate 3 – label “pretreatment – bleach”
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Plate 4 – label “pretreatment – iodine”
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ADD AGAR TO PLATES 1-4
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Perform step 3 – allow to stand for 30 minutes
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Perform step 4
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Plate 5 – label “post-treatment bleach”
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Plate 6 – label “post-treatment iodine”
Follow handout, BE SURE TO ADD AGAR IMMEDIATELY TO PLATES 1-4 AFTER YOU TAKE PRETREATMENT SAMPLE
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Pre- treat bleach (E.coli added to tap water, “contamination”)
Post treat bleach (Bleach added, sat for 30 minutes, successfully disinfection)
Ultraviolet light: Lethal effects – Lab 19
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Table in lab 19
o Change B. megaterium to B. subtilus
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Bacillus megaterium is an endospore former while Staphylococcus aureus isn’t – how does this make a
difference?
o Each student will be assigned with species and time
o Obtain TSA plate
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Take sterile swab and dip in sample (use aseptic technique)
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Wipe entire plate with swab (want to cover the plate with bacteria)
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Label plate with initials, species, and exposure time (write small) - refer to table
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Take lid off (except if are #8 or 16), place note card over half of plate, then place in UV chamber for assigned
time
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#15 or 16 – place with lid on plate in chamber for 30 minutes instead of 60
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S. aureus, 10 seconds
B. subtilus, 10 minutes
Evaluation of Antiseptics – Lab 24
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Antiseptics
o Sporocides – destroy all microbial life, including endospores
o Sanitizers – kill most but not all
o Bacteriostatic – inhibits growth but does not kill
o Bacteriocidal – kill bacterial cells
Each bench will be split into groups of 2 (2 TSA plates per group)
Antiseptics are on bench for each groups, so are paper disks
On bottom of petri dish, use marker to divide plate into 3 sections
Label plate with initials, species, and mark each section as to what antiseptic is used (write small)
Using a swab, gain a sample of S. aureus and cover TSA agar (want “blanket” of bacteria) ; then put disks soaked in antiseptic on
plate; do same on other plate for P. aeruginosa
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S. aureus
P. aeruginosa
Remember to take PDA plate home with you!!!!! Set it out to capture some Fungi 