Antibiotic Resistant Lab

Antibiotic resistance of bacteria

Procedure Using a sterile loop, pick an isolated colony from you bacterial plate. Try to find one that grew well but is all by itself. Move the colony (don’t scoop up the agar) to a new plate. Using a moist, sterile, cotton swab, spread the bacteria around on the plate.

The goal is to get an complete, even, coverage of bacterial growth on the plate (called a “lawn”). Remember to open the plate only minimally, using the lid as an “umbrella” to prevent contamination (see image below). Label each plate on the bottom (agar contaning side) and store it for examination during next week’s lab.Each new prepared plate will receive four paper discs containing antibiotics. We will be using several different types of Antibiotics and/or antimicrobials.

(please fill in which antibiotics you used below)

  • 1
  • 2
  • 3
  • 4

The antibiotic discs come in a little tube-like dispenser. To remove the discs take a sterile toothpick and push out a disc into your plate. Use the toothpick to gently press the disc onto the agar. Once you have added the five antibiotic discs to your plates, make sure the plates are labelled and store them in the back of the lab until next week.

If the bacteria are susceptible to the antibiotic a zone of inhibited growth will be evident next week. Measuring the size of this zone is a relative indication of the effect of the antibiotic on the particular bacteria.

Bacteria possess several characteristics that enable them to become resistant to antimicrobial drugs:

  • Asexual reproduction
  • Short generation times
  • High mutation rates

Some Information on Antibiotics


1. Name two ways (1. and 2. ) that common human practices towards antimicrobials aids bacteria in becoming resistant.


2. Name two reasons your Physician will perform cultures such as the ones you have done in this lab.



4. How are materials are collected for cultures?



5. Why is neccesary to use sterile technique when obtaining cultures?