VPE 511: Environment and Environmental Hygiene (2+1)

PRESUMPTIVE TEST

• In presumptive test, only the presence of coliforms are identified.

Durham’s Tube Test

• In this test lauryl tryptose mannitol broth is used. 

Materials Required

• Test tube with durham’s tube
• 10 ml and 1 ml pipette
• Lauryl tryptose mannitol broth
• Incubator
• Water sample                                        

Procedure

• 5-8 ml of lauryl tryptose mannitol broth is taken and 1 ml of water sample is added in a test tube.
• Durham’s tube is placed along with the broth.
• The test tubes are incubated at 440C for 18-24 hours.

Interpretation

• In positive samples, E.coli present in the water utilizes the lactose and produces acid and gas.
• Acid production leads to change in colour of the medium.
• Gas produced accumulates and the Durham’s tube rises to the surface.