Durham tube

Durham tubes are used in microbiology to detect production of gas by microorganisms.

The culture media to be tested is then added to the larger tube and sterilized, which also eliminates the initial air gap produced when the tube is inserted upside down.

[1] Litmus solution can also be added to the culture media to give a visual representation of pH changes that occur during the production of gas.

[3] However, Durham argued that quantitive measurements are of limited value because of the culture solution will absorb some of the gas in unknown, variable proportions.

[3] Additionally, using Durham tubes to provide evidence of fermentation may not be able to detect slow- or weakly-fermenting organisms when the resultant carbon dioxide diffuses back into the solution as quickly as it is formed,[4] so a negative test using Durham tubes does not indicate decisive physiological significance.