Week 8:
Ex. 10--Microbial Sensitivity Testing: Antibiotic Sensitivity Testing--Kirby-Bauer Technique (DEMO), pp. 100-106
- Discuss results from last week: UV and chemical sensitivity. Compile class results.
- This exercise will be done as a demonstration. Students will measure zones of inhibition and put their
results together as a group. We will need six sets of large Mueller-Hinton agar plates with the correct depth
of agar and properly swabbed with each of six organisms (total 36 plates), antibiotic disks placed on them,
and incubated 24-48 hours, sealed with tape, and refrigerated.
- TA's will prepare the plates the Thursday before we need them and incubate; if they are ok, refrigerate until Tuesday.
(Otherwise, make more!) Seal with tape so they don't dehydrate, and so that the early sections don't mess
them up for the later sections. Save them for the Thursday lab!
- Be sure to explain how these are used clinically, why and how these are standardized, why you have to
use a table and measurement alone is not enough, that it is the bacteria that are susceptible/sensitive to the antibiotic
and not vice versa, and why and how bacteria might be resistant to an antibiotic.
Lab Orders for Week 8
- For instructors---
- Equipment:
- disk dispensers (or forceps and alcohol), various fresh (?) antibiotic disks (preferably from among the ones listed in Table 25.1 in the lab manual, pp. 154-155, choosing some for G+ organisms and some for G-), sterile swabs (at least 36)
- Cultures:
- Staphylococcus aureus (or a different staph.), Streptococcus pyogenes (or a different strep.),
Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Salmonella spp., Shigella spp.
- Media (consult Dr. Wilson before preparing media):
- 36 large Mueller-Hinton agar plates, poured as for Kirby-Bauer standard procedure (see lab manual)
- For class---
- Equipment:
- rulers, standard antibiotic susceptibility tables