Week 7:
Ex. 10: Microbial Sensitivity Testing: Physical Methods--Ultraviolet Light Sensitivity, pp. 93-95, and
Ex. 10: Microbial Sensitivity Testing: Chemical Methods--Chemical Sensitivity, pp. 98-99

1. Vocabulary: see p. 102
2. We're not doing the heat sensitivity or cold temp/freezing parts of this exercise on pp. 96-98.
3. Half of the groups will do the UV exercises; half will do the disinfectant/antiseptic exercises. I suggest that one end of each bench do the UV part and the other end the disinfectant/antiseptic part to make it easier for them to share results later.
4. For the UV exercise, it is very important to pre-test the procedure to optimize it for the media and cultures that we will actually be using. TA's--please do this! I can help if we schedule a time far enough in advance. We will use the procedure in the lab manual.
5. There is a table on p. 95 that students can follow to record their results, substituting the actual times used in lab.
6. Explain the effect that ultraviolet light has on bacteria and on surfaces, including why it has little effect below the surface (non-penetrating non-ionizing radiation).
7. Growth will be evaluated after a 24-48 hour incubation (NG, +, ++. +++, ++++ for control, etc.).
8. Each group should report its results at the next class period in order to compile a set of class results, which they should report and compare for their lab reports.
9. For the disinfectant/antiseptic exercise, we will follow the procedure in the lab manual, pp. 98-99.
10. There is a table on p. 99 that students can follow to record their results.
11. Make sure the students understand the difference between an antiseptic and a disinfectant.
12. There is also an informational handout on disinfectants and antiseptics, since I do not cover this in lecture. Students are responsible for knowing the material in this handout.
13. Lab Quiz 3! Covers weeks 5 and 6: carbohydrate and protein catabolism.

Cultures:

For 18 groups: Well grown broth cultures of Serratia marcescens, Bacillus subtilis, and Bacillus cereus (I suggest growing these cultures in flasks of 100 ml of nutient broth on the shaker for at least 48 hours, and aliquoting them into sterile tubes for class.)

Media:

(18 groups) 9 nutrient agar or T-soy agar plates (for the UV exercises)

Equipment:

UV light set up for the appropriate distance from the plates

Safety glasses as needed

Sterile cotton swabs

Cultures: For 18 groups: Well grown broth cultures of Escherichia coli, Staphylococcus epidermidis, and Pseudomonas aeruginosa (I suggest growing them in three largish flasks of nutient broth on the shaker for at least 48 hours, and aliquoting them into sterile tubes for class.)

Media:

(18 groups) 3 nutrient agar plates (for the disinf/antiseptic exercises)

Equipment:

Millimeter ruler (for measuring results)

Sterile filter paper disks in either aluminum foil packets or glass beakers covered with foil, 3 beakers/packets per lab section with at least 15 disks in each one.

Forceps in alcohol in small glass beakers

Sterile cotton swabs

Reagents:

Assorted disinfectants and antiseptics, plus what students bring in