REQUIRED PRACTICAL 6 - GROWTH OF BACTERIA/ASEPTIC TECHNIQUES Flashcards
the use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth
what is the purpose of this practicals
- aseptic techniques are used to avoid contamination of the sample from outside substances, like microorganisms
- important to get reliable and repeatable data
what are aseptic techniques and explain their purpose
- wipe down surfaces with antibacterial cleaner before and after experiment
- use a bunsen burner in the work space so that convection currents draw microbes AWAY from the culture
- flame the wire loop before using it to transfer bacteria
- flame the neck of any bottles before using them to prevent any bacteria from entering the vessel
- keep all vessels containing bacteria open for the minimum amount of time
- close windows and doors to limit air currents
what is the equipment needed for the practical
- bacteria sample
- disinfectant
- bunsen burner
- heatproof mat
- ethanol
- wire hoop
- pipette
- forceps
- plastic spreader
- prepared agar plate
- antibiotic ring
- ruler
what is the method for this practical
- carry out the aseptic techniques
- use a sterile pipette or wire hoop to transfer bacteria from broth (distilled water, bacterial culture or nutrients) to the agar plate
- spread bacteria evenly over the plate using a sterile plastic spreader
- use sterile forceps to place a multi disc antibiotic ring on the plate, the ring should only be moved by holding the centre NOT the arms
- lightly tape a lid on, invert and incubate at 25 degrees C for 48 hours
- for this ^, do not tape around the entire dish as this prevents oxygen entering and promotes the growth of more harmful anaerobic bacteria
- sterilise equipment used to handle bacteria and disinfect work surfaces
- post incubation, measure the diameter of the inhibition zone (clear circle) for EACH antibiotic however do not remove the lid from the agar plate
- work out the area of the inhibition zone
what formula is used to work out the inhibition zone
A = pi x diameter^2/4
what are the potential risks for this practical
- disinfectant
- biohazard
- naked flame
what is the risk for the disinfectant
flammable
what is the safety precaution for the disinfectant
keep away from the naked flame
what is the risk for the biohazard
- contamination
- infection
what is the safety precaution for the biohazard
- use disinfectant
- wash hands with soap after dissection
- do not incubate at human body temp
- do not open agar plate post incubation
what is the risk for the naked flame
- fire hazard
- burns
what is the safety precaution for the naked flame
- keep away from flammable materials
- tie up long hair
- wear goggles
what are the conclusions for the practical
- if there is a LARGER inhibition zone around the antibiotic, it has killed more bacteria
- the larger the inhibition zone, the better the antibiotic zone
- some antibiotics will have no/very little inhibition zone, this shows that bacteria are resistant to this antibiotic and are NOT killed by it
why is it important to maintain a pure culture of bacteria
- bacteria may outcompete bacteria being investigated or may be harmful to humans/pathogenic
why lightly tape/hold the lid with 2 pieces of tape instead of sealing it completely
- allows oxygen in, preventing growth of ANAEROBIC bacteria as they are more likely to be pathogenic/harmful to humans
