Micro-organisms,most effective antibiotic to act against the two types of bacterium: E.coli and B.subtilis.

Apparatus and equipment used:

• 2 x bottles of molten nutrient agar
• 2 x sterile Petri dishes
• 1 x bottle containing bacteria – 1ml Bacillus subtilis
• 1 x bottle containing bacteria – 1ml Escherichia coli
• 1 x Petri dish containing two antibiotic mastrings (disc containing eight different antibiotics)
• 1 x metal forceps
• 1 x Bunsen burner and mat
• 1 x scissors
• Matches
• Sellotape
• Glass marker pens

The antibiotics on the mastring:

Amp - Ampicillin

Chl - Chloramphenicol

Ery – Erythromycin

Met - Methicillin

Pen – Penicillin

Str - Streptomycin

Sfz – Sulphafurazole

Tet – Tetracycline

An antibiotic is a  that kills or slows the growth of  and other germs. Antibiotics are one class of , a larger group which also includes anti-viral, anti-fungal, and anti-parasitic drugs. They are relatively harmless to the host, and therefore can be used to  

Step by step of the method I followed:

The practical was split into two stages.

The method I used included aseptic technique. Aseptic technique is a set of specific practices and procedures performed under carefully controlled conditions with the goal of minimizing contamination by pathogens. Aseptic technique helps to prevent or minimize infection

Before I begun the practical, I sprayed the area in front of me with a disinfectant.

Stage 1

1. I first put on a laboratory coat to protect me and my clothes and wore safety glasses to protect my eyes and also disposable gloves since I will be dealing with bacteria.
2. I placed the Bunsen burner on the mat and lit it to leave it on invisible flame.
3. I then waited till the molten agar is hand hot so I could hold it comfortably in my hand and then unscrewed the bottle gently and carefully.
4. To kill of any germs at the top of the bottle and to sop decontamination I passed the neck of the bottle through the flame a few times.
5. I gently unscrewed the bottle of bacteria – E.coli and passed the neck of the bottle through the flame.
6. I then added the E.coli to the bottle of agar, passed the bottle gently through the flame then screw the lid back on. I then inverted the bottle four times slowly and carefully
7. Next I took one of the sterile Petri dishes I was provided with and snipped the sellotape on the side facing away from me. I had to make sure I didn’t open the Petri dish in case any dust would get in.
8. I then unscrewed the bottle containing the agar and E.coli and passed the neck through the flame again then lifted the lid of the Petri dish, away from me and poured the agar and E.coli in I then closed the lid and placed the empty bottle that had E.coli on top of the Petri dish so I knew which bacteria I had put in.
9. I repeated the steps above for the other bottle of bacteria – Bacillus subtilis

Stage 2

1. I waited for a couple of minutes until the agar in both of the Petri dishes had set. I passed the top of the forceps through the flame to kill of any germs that it may have had.
2. The mastrings had a paper tab at the centre, I used the paper tab to slowly lift the mastring from the dish and placed it in the centre of the plate and pressed it down gently. I repeated this for the plate.
3. I added a piece of sellotape over the area on each of the Petri dishes I snipped earlier.
4. I turned the dish over and used a glass marker pen to write my initials, teacher’s initials and the bacteria in the plate.  
5. I disinfected the area I worked on again to make sure I didn’t leave any bacteria on the area then wash my hands using liquid to make sure it was clean and didn’t contain any bacteria.

Diagram of what I did:

I tested the antibiotics on a bacterial lawn. A bacterial lawn is a continuous cover of bacteria on the surface of a growth medium. It is the appearance of   when all the individual colonies on a Petri-dish  merge together to form a field of bacteria

Table to show which antibiotic was the most effective

The diameter of the clear zone around each antibiotic indicates how effective it is at killing the bacteria

To decide which the most effective antibiotic is I will look at the ‘Most effective by rank’ column to see which antibiotic is ranked 1st. I ranked each antibiotic by measuring the diameter of the clear zone around each antibiotic. The larger in length the diameter, the more effective it is.

The most effective antibiotic is therefore ‘Chloramphenicol’ since it had the largest diameter for both types of bacteria.