Microbiology: antibiotics and antiseptics
Method overview
Use aseptic technique to spread bacteria evenly on sterile agar. Add equally sized antimicrobial discs with sterile forceps, include a sterile-water control, tape the lid at a few points, incubate inverted at 25°C in school laboratories, then measure inhibition zones without opening.
Apparatus set-up
Diagramsterile agar plate; bacterial culture; sterile swab; forceps; paper discs; disinfectants/antibiotics; tape; incubator; ruler
Independent variable
type or concentration of antimicrobial
Dependent variable
diameter or area of zone of inhibition
Control variables
bacterial species; agar depth; disc size; volume/concentration; incubation time and temperature
Apparatus
sterile agar plate; bacterial culture; sterile swab; forceps; paper discs; disinfectants/antibiotics; tape; incubator; ruler
Safety
Disinfect benches, minimise lid opening, use sterile equipment, tape but do not fully seal, incubate at 25°C and do not reopen grown plates.
Scientific rationale
Aseptic technique prevents contamination; inverted incubation stops condensation dripping; 25°C reduces growth of harmful human pathogens; a control shows whether the solvent/disc affects growth.