Lab 2 - Oxygen requirements

Question 1

What are the 3 divisions of anaerobes?

Answer 1

1. Facultative anaerobes = don’t require, grow better
2. Aerotolerant anaerobes = not sensitive to presence/absence
3. Obligate anaerobes = don’t tolerate

Question 2

What are the key components of thioglycollate broth? What is it generally used for?

Answer 2

Use = microbe relationships to O2
- Thioglycollic acid and cysteine = reduce total O2 to H2O
- 0.075% agar = reduce O2 by slowing its diffusion
- Resazurin dye = indicator of O2 when red and colourless when none

Question 3

Describe how to perform stab inoculate and why it’s done

Answer 3

Stab loop down to bottom of tube and remove straight back out to minimise O2 introduction

Question 4

What is the relationship Clostridium sporogenes and Pseudomonas aeruginosa have with O2?

Answer 4

Clostridium sporogenes = Gram positive rod, anaerobic
Pseudomonas aeruginosa = Gram negative rod, aerobic

Question 5

Briefly describe the method used in this experiment to investigate the oxygen requirements of different bacteria

Answer 5

1. Stab inoculate THIO and TSB broths with Pseudomonas aeruginosa
2. Stab inoculate THIO and TSB broths with Clostridium sporogenes
3. Stab inoculate TSB broth with both bacteria
4. Incubate for 24hrs at 37C

Question 6

What are the expected results of this experiment for each broth type?

Answer 6

• Resazurin dye in THIO broth turns red when oxygen present
• TSB is used for anaerobic growth and becomes turbid if growth present