PRACTICAL WRITEUP 27/02/2022
Use of aseptic techniques to investigate the effect of antimicrobial substances in microbial growth
(Practical 6 Biology.)
Aim of the experiment: Effect on different antibiotics on the bacteria
Independent Variable: The type of the antibiotic used
Dependent Variable: Zone of the inhibition left by the antibiotic (area measured in cm 3
Variables kept control
->Same concentration of antibiotic used
->Type and amount of bacteria used – E.coli will be used as the bacteria and it will be evenly
spread across an agar medium
->Volume of antibiotic used for each disc were the same
->Contamination of culture – aseptic techniques and sterile equipment used to avoid
contamination of bacteria culture
->Temperature of cultures – all Petri dishes should be incubated overnight at 25°C
->pH of medium was kept neutral for all the agar plates
Safety precautions:
• Hair tied back to mitigate risk of accidental burning
• Washing of hands and sanitising/disinfecting workspace before and after to prevent contamination
If test tube broken, inform teacher to prevent injury or inadequate removal of glass.
• Bunsen burner always on safety flame if roaring flame not in usage.
• Disinfectant flammable. Keep away from naked flame.
Part A: Measuring the effects of antimicrobial substances on the growth of bacterial populations in
the culture.
Apparatus
→ Small McCartney bottle containing broth culture of bacteria. Bunsen burner. Pipette. Plastic
sterile spreader. Beaker containing Virkon (disinfectant.) Measuring cylinder. Agar plate containing
growth medium (x5) and 4 test tubes. As well as tape and marker.
Procedure/methodology
→ Firstly, we practiced the technique to open an empty McCartney bottle 1 one hand, placing neck
of bottle on roaring flame of Bunsen burner and closing it again. This was e to minimise
contamination from undesired microorganisms. Secondly, we prepared serial dilutions of bacterial
broth. In first test tube, used measuring cylinder and pipette to measure out of water and lcm of
bacterial broth into first test tube. Then extracted 1cm from first test two poured it into second test
tube and used measuring cylinder to dilute it with 9cm of water. Cess continued for until 4 serial
dilutions prepared. Er preparing the serial dilutions we used the McCartney bottle technique to
Use of aseptic techniques to investigate the effect of antimicrobial substances in microbial growth
(Practical 6 Biology.)
Aim of the experiment: Effect on different antibiotics on the bacteria
Independent Variable: The type of the antibiotic used
Dependent Variable: Zone of the inhibition left by the antibiotic (area measured in cm 3
Variables kept control
->Same concentration of antibiotic used
->Type and amount of bacteria used – E.coli will be used as the bacteria and it will be evenly
spread across an agar medium
->Volume of antibiotic used for each disc were the same
->Contamination of culture – aseptic techniques and sterile equipment used to avoid
contamination of bacteria culture
->Temperature of cultures – all Petri dishes should be incubated overnight at 25°C
->pH of medium was kept neutral for all the agar plates
Safety precautions:
• Hair tied back to mitigate risk of accidental burning
• Washing of hands and sanitising/disinfecting workspace before and after to prevent contamination
If test tube broken, inform teacher to prevent injury or inadequate removal of glass.
• Bunsen burner always on safety flame if roaring flame not in usage.
• Disinfectant flammable. Keep away from naked flame.
Part A: Measuring the effects of antimicrobial substances on the growth of bacterial populations in
the culture.
Apparatus
→ Small McCartney bottle containing broth culture of bacteria. Bunsen burner. Pipette. Plastic
sterile spreader. Beaker containing Virkon (disinfectant.) Measuring cylinder. Agar plate containing
growth medium (x5) and 4 test tubes. As well as tape and marker.
Procedure/methodology
→ Firstly, we practiced the technique to open an empty McCartney bottle 1 one hand, placing neck
of bottle on roaring flame of Bunsen burner and closing it again. This was e to minimise
contamination from undesired microorganisms. Secondly, we prepared serial dilutions of bacterial
broth. In first test tube, used measuring cylinder and pipette to measure out of water and lcm of
bacterial broth into first test tube. Then extracted 1cm from first test two poured it into second test
tube and used measuring cylinder to dilute it with 9cm of water. Cess continued for until 4 serial
dilutions prepared. Er preparing the serial dilutions we used the McCartney bottle technique to
