Week 10
Posted by drstocksblog on October 31, 2009
Exercise 13: Testing Disinfectants
- View the comic in Vancko Hall.
- Work in teams of three students.
- Each student prepares a lawn of differenct bacteria on the surface of a plate of agar following the directions. The bacteria are:
- E. coli, Staphylococcus aureus, Salmonella sp.
- Then follow the directions and test the same set of disinfectants on each plate.
- Plates are then incubated at 37 degrees C for 48 hours and the zone of inhibition is measured to determine which worked the best against which bacterium.
Exercise 15: Identification of Gram Negative Bacteria
- Work in groups. Each lab will have 6 groups because we are using 6 species of bacteria:
- E. coli
- Enterobacter aerogenes
- Alcaligenes faecalis
- Salmonella sp.
- Proteus vulgaris
- Pseudomonas aeruginosa
- One of the most important things is to GET ORGANIZED — pick a person to keep a check-list of media and to be sure that all tubes are inoculated.
- Be sure that all tubes are labeled in such a way that if the person doing the labeling is absent for the return lab, other members of the group can identify the tubes as to bacterium and type of medium.
- Each group will get a known gram negative bacterial culture and an unknown gram negative bacterial culture.
- BE SURE TO RECORD THE NUMBER OR LETTER OF THE UNKNOWN.
- Then you will inoculate TWO sets of microbiological media: one set with the known and the other with the unknown.
- Your inoculated cultures will be incubated for 48 hours and then you will collect results for your known and unknown.
- Basically you are looking for products of reactions that indicate the bacteria were able to utilize the substrate, i.e. sugar or amino acid, given them in the medium.
- Sometimes you just look at the tube for a color change; for some media you must add reagents.
- Results of the knowns will be shared so that you can try and figure out what your unknown was.
- Media will include the following:
- OF glucose — agar deeps (one with air and one shielded from air)
- Fermentation Broths with phenol red containing sugars:
- Glucose
- Lactose
- Sucrose
- MR-VP Medium — a broth
- Simmons Citrate Agar slants
- Urea Broth
- Phenylalanine agar slants
- SIM medium (semi-solid agar deeps)
- Nitrate broth
