Unknown bacteria are often tested for their antibiotic resistance or sensitivity in the microbiology lab. Not only is resistance an important thing to know when deciding on an antibiotic treatment for a patient, but some antibiotic sensitivity tests are useful in identification of microbes.
VUMIEtm 2012 simulates testing of antibiotic sensitivity through a modified Kirby-Bauer sensitivity plate method. Bacteria from a pure culture of the unknown are used to seed the surface of the agar plate, and then paper disks impregnated with known amounts of antibiotics are placed on the agar surface. The antibiotics diffuse into the agar and away from the disks, creating gradients where the concentration is high near the disk and dissipates as the distance from the disk increases. The plate is incubated overnight and the bacteria seeded on the agar surface grow and replicate. Were there no antibiotic disks, the bacteria would create a bacterial lawn. But if an antibiotic prevents bacterial growth, the microbe will not grow in the region surrounding the disk, leaving a zone of inhibition. At the point where the concentration of diffusing antibiotic has fallen below toxic levels, the lawn grows in, leaving a distinctive pattern of zones of inhibition reflecting which antibiotics are toxic to the microbe. The size of the zones is compared to known standards for each antibiotic to allow interpretation of the results as "sensitive" (the microbe is sensitive to the antibiotic), "intermediate" (the microbe is marginally sensitive), or "resistant" (the antibiotic is not effective for killing this microbe).
To see how this works in the micro lab, open VUMIEtm 2012 and Micro Digital Media Exercise 7 "Antimicrobial and Chemotherapeutic Agents".
Follow your instructor's direction on what documentation to turn in at the completion of this activity: VUMIEtm 2012 Virtual Lab Report, MDM Exercise 7, or other.
When done, you may be asked to take a quiz over the material.