Lab 5 - Antimicrobials

Question 1

What was the first instance of a microbe producing an antibiotic?

Answer 1

1897 Ernest Duchesne = Penicillum glaucum inhibited bacterial growth

Question 2

Which genus is responsible for the most antibiotics?

Answer 2

Streptomyces from Actinomycetes

Question 3

Explain how the cross-streak method works

Answer 3

1. Obtain pure cultures of sample
2. Grow isolate on agar
3. Excreted antimicrobial diffuses thru agar
4. Cross-streaked bacteria may be inhibited

Question 4

Is Streptomyces more effective against Gram negative or positive bacteria overall?

Answer 4

Gram negative (also effective against some Gram positive)

Question 5

Briefly describe the method of this experiment

Answer 5

1. Inoculate TSA plates with 1 Streptomyces species each
2. Incubate 10 days at room temperature
3. Inoculate loopfuls of bacteria culture onto plates parallel to Streptomyces growth
4. Incubate overnight at 37C
5. Measure inhibition in mm and estimate growth density using given charts

Question 6

Which bacteria was consistently resistant to inhibition?

Answer 6

Pseudomonas aeruginosa