Antimicrobial subtances

• What do i need to know how to do?

  Investigate effect of antimicrobial substances on microbial growth, using ASEPTIC TECHNIQUES
• Give an example of an antimicrobial substance?

  • Antibiotic
  • Antiseptic
  • Disinfectant
• Where will the bacteria used been grown in?

  A liquid broth (a mixture of distilled water, bacterial culture and nutrients)
• How to transfer BACTERIA FROM BROTH TO AN AGAR PLATE?

  Use sterile pipette

  Spread bacteria over plate using a sterile plastic spreader
• What is an agar plate?


  A petri dish containing agar jellu
• What do you do once bacteria is on agar plate?

  Use STERILE FORECEPS to place paper discs SOAKED with DIFFERENT ANTIBIOTICS spaced apart on the plate
• What must you add to the plate?

  a negative control disc soaked only in sterile water
• describe the negative control disc?

  Soaked only in sterile water
• What do you do once bacteria + paper discs are on agar plate?

  LIGHTLY TAPE a lid on, invert, and incubate plate at 25c for 48hours

  • Allows bacteria to grow and form a 'lawn;
• describe the inhibition zone?


  Anywhere the bacteria cannot grow can be seen as a clear patch in the lawn of bacteria = inhibition zone
• What do the sizes of an inhibition zone tell you?

  How well an antibiotic works
• Larger inhibition zone =?

  more bacteria inhibited from growing
• What can a similar technique be used to do?

  Test effects of antiseptics or disinfectants on microbial growth