The proce • A pour plate culture of the bacterium Bacillus subtilis was prepared according to
the aseptic method, using nutrient agar as the growth medium.
A fixed amount of inoculum is placed in the centre of a sterile petri dish.
A ring of eight discs (1 to 8) was then placed on the inoculated culture.
Each of the discs 2 to 8 contained a different antibiotic.
Disc 1 had no antibiotic.
• The plate was incubated for 48 hours at 35°C.
The diagram below shows the results obtained after the incubation period.
bacterial
growth
bacterial growth
inhibited
Adapted from UCLES 2012 0510/32/0/N/12​