About this test
What is the purpose of this test?
The purpose is to see how varying levels of oxygen impact the growth of the unknown microbe.
How are oxygen requirements determined?
Bacteria vary greatly in their need for oxygen to support growth. Aerobic species of bacteria require atmospheric levels of oxygen for growth while anaerobes are killed by attempted growth in oxygen. Some species only tolerate specific intermediate levels of oxygen in their growth environment, and do not grow well at either the top of the medium or the butt of the tube.
A medium is used that contains chemicals creating aerobic conditions at the surface and anaerobic conditions in the butt, with varying levels of oxygen found between the two extremes. The unknown is then inoculated into in the medium, and the pattern of growth observed after incubation reveals the impact of oxygen levels on growth.
What medium is used?
The medium used in VUMIE Online for determination of oxygen requirements is fluid thioglycolate broth. This is an agar-thickened broth that features chemicals supporting formation of a gradient of oxygen with full oxygen levels at the surface and oxygen-free levels in the butt of the tube.
How is the test performed?
The medium is inoculated with a pure culture of the unknown organism and incubated overnight. The location in the broth where growth is found indicates the oxygen requirements for the unknown organism.
What reagents are added?
None
Performing this test in the VUMIE Online lab.
Inoculation of the Medium
Complete the process of a tube-to-tube aseptic transfer to inoculate the medium. Forgotten how to do these things? Watch the “Show Me How To” videos.
Incubation of the Inoculated Medium
Place the inoculated tube into the 35-37 C.
Press the New Day button to move forward 24 hours. Forgotten how to do these things? Watch the “Show Me How To” videos.
Determination of Results
Incubate this test for only 24 hours.
Retrieve the incubated culture from the incubator.
No reagents are required for completion of this test.
Results will conform to one of these four growth patterns:
- Strict aerobic growth (also known as “obligate” aerobic growth). Turbidity is seen at the top of the tube but NOT at the bottom.
- Strict anaerobic growth. Turbidity is seen only at the bottom of the tube.
- Facultatively anaerobic growth. This is the pattern seen for those bacteria that can grow with or without oxygen. Turbidity is seen throughout the tube.
- Microaerophilic growth. Some bacteria cannot grow with unlimited oxygen or without oxygen, needing a modest amount of oxygen. A thin band of turbidity is seen below the top of the medium and above the bottom of the tube.
Record your test result. Forgotten how to do these things? Watch the “Show Me How To” videos.