biology - microbiology Flashcards
1
Q
what antiseptic techniques can be used to avoid contamination?
A
- spray work area with disinfectant spray and wipe dry
- wash hands with antibacterial wash
- flame the neck of the culture bottle
- lift the lid of agar plate at an angle
- dip spreader in ethanol and pass through bunsen flame before spreading bacteria
- use forceps to place antibiotic discs
2
Q
how to investigate the effect of antibiotics on bacterial growth using zones of inhibition?
A
- divide agar plate with bacteria into three segments
- use forceps to place filter paper disc with antiseptic in each zone
- loosely tape lid onto the agar plate (to allow oxygen to reach the bacteria)
- incubate at 25°C for 48 hours
- measure the diameter of each clear zone (zones of inhibition) using a ruler
- calculate mean diameter
- calculate the area of clear zones
3
Q
how to measure the zone of inhibition (clear zones)?
A
- 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
4
Q
why should you not completely cover seal the agar plate?
A
to allow oxygen to enter the bacteria, preventing the growth of harmful anaerobic bacteria
5
Q
why is it necessary to measure the diameter of a clear zone twice?
A
clear zones are not always uniform (symmetrical) so taking more than one measurement allows for a mean to be calculated
6
Q
what formula is used to calculate the area of the zone of inhibition?
A
area = π X radius^2
