DETERMINE THE BACTERIAL POPULATIONS SENSITIVITY TO A RANGE OF ANTIBIOTICS.
- This can be done by placing small disks of filter paper or agar impregnated with various types of antibiotics onto the bacterial lawn. The bacteria are allowed to incubate for a day or two, and then the plate is examined to see whether the bacterial growth is inhibited (or not) by the antibiotics on each disk.
- SENSITIVE: In this case, a clear, circular "halo" (technically known as a "plaque," or zone of inhibition) will appear around the antibiotic disk, indicating an absence of bacteria. The antibiotic has inhibited their growth and/or killed them, meaning that this particular antibiotic should be effective against the infection your rabbit has.
- INTERMEDIATE: A somewhat cloudy plaque indicates that not all the bacteria in the area around the disk have been killed. This means that there are some members of the bacterial population that are sensitive to this particular antibiotic, but others that are genetically immune to its effects. If an antibiotic to which the bacteria show "intermediate" sensitivity is used, it is likely that the sensitive members of the bacterial population will be killed, and the resistant ones will survive, resulting in the selection of a population resistant to that particular antibiotic.
- RESISTANT: In this case, the filter paper will have no discernable plaque around it, meaning that the bacteria are growing normally, even in the presence of the antibiotic. An antibiotic producing no plaque will most likely be ineffective against the bacteria causing your bunny's infection.
In modern laboratories, bacteria are usually identified by characterization of the genome: identifying the characteristics of the DNA and RNA of a sample species. This type of testing is generally considered more reliable (and soon, less expensive) than actually growing bacterial cultures and exposing them to various types of antibiotics to see which drugs kill or inhibit the bacterial growth. But if more than identification is required, and if an antibiotic that usually works against a particular bacterial strain is ineffective, then it may be necessary to actually grow the bacteria and perform an "old fashioned" culture and sensitivity test.