RP2 MIcrobiology

Question 1

what antiseptic techniques can be used to avoid contamination?

Answer 1

• spray working area with disinfectant and wipe dry
• wash hands with antibacterial wash
• flame the neck of the culture bottle
• lift the lid of the agar plate at an angle
• dip spreader in ethanol and pass through Bunsen flame before spreading bacteria
• use forceps to place antibiotic discs

Question 2

describe how you could investigate the effect of antibiotics on bacterial growth using zones of inhibition

Answer 2

• divide agar plate with bacteria into three segments
• use forceps to place filter paper disc with antiseptic in each zone
• loosely tape lip onto agar plate to allow oxygen to reach bacteria
• incubate at 25°C for 48 hours
• measure the diameter of clear zones (zoneas of inhibition) using a ruler from two opposite directions - calculate mean of measurements
• calculate area of clear zones

Question 3

how would you measure the zone of inhibition?

Answer 3

use a ruler to measure from a point on one side to a point directly opposite (with lid still in place)
measure again at 90° to first diameter measurement in order to calculate a mean

Question 4

why should you not completely seal the agar plate?

Answer 4

to allow oxygen to enter the agar plate, preventing the growth of harmful anaerobic bacteria

Question 5

why is it necessary to measure the diameter of the zone of inhibition twice?

Answer 5

clear zones are not always uniform - taking more than one measurement allows a mean diameter to be calculated

Question 6

what equation is used to calculate the area of clear zones?

Answer 6

area = πr^2