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Lab 28 Goals and Objectives:
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Exercise 31: Lethal Effect of UV Light
Exercise 33: Effectiveness of Alcohol as an Antiseptic
Exercise 36: Effectiveness of Hand Scrubbing
Exercise 34: Antimicrobial Sensitivity Testing
Exercise 35: Evaluation of Antiseptics
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Exercise 31: Lethal Effect of UV Light
Score plates (+++, ++, +, -) for growth using control side of each plate
as +++ for comparison; record on class sheet
Read results
Exercise 31: Lethal Effect of UV Light
Score plates (+++, ++, +, -) for growth using control side of each plate
as +++ for comparison; record on class sheet
UV Exposed side
Cover half
with paper
card
Control
(was covered)
Exercise 33: Effectiveness of Alcohol as an Antiseptic
Calculate percent reduction for control, dip and swab
Colony count 1st press = 100%
Colony count 1st press – Colony count 2nd press = reduced number of
bacteria
(Colony count 1st press – Colony count 2nd press)
Percent reduction =
x 100
Colony count 1st press
Exercise 38: Effectiveness of Hand Scrubbing
Calculate CFU/ml for each scrubbing round: don’t forget to multiply
by dilution factors:
0.1ml → x 10 (0.1ml is 1/10 of 1ml)
0.2ml → x 5 (0.2ml is 1/5 of 1ml)
0.4 ml → x 2.5 (0.4ml is 2/5 of 1ml)
Exercise 34: Antimicrobial Sensitivity Testing
• Disk-Diffusion Test (Kirby-Bauer test) is used in determining what
treatment of antibiotics should be used when treating an infection
– to determine the inhibition of bacterial growth measured under standard
conditions
– a culture medium - the Mueller-Hinton agar
– plate lawn of bacteria and place disks of known antimicrobials on the lawn
– measure zones of inhibition (total diameter in mm)
• Record millimeter diameter on class data chart
• compare to a standard table for that drug
– Sensitive
– Intermediate
– Resistant
• Determine if organism is resistant,
sensitive, or intermediate
Figure 20.17
Exercise 35: Evaluation of Antiseptics
Note different effects Gram + vs Gram – for some agents