Add 1ml sterile saline to a  sterile screwcap test tube

Use a sterile  spade/applicator stick to emulsify in the saline two spadefuls of growth from a four-week-old culture

Use sterilised forceps and carefully insert a nitrate test strip (arrow indicates which end to insert first); do not  let the strip contact any fluid on the side of the tube

Cap the tube tightly and incubate in a vertical position at 37EC for two hours

After one hour of  incubation, shake the tube gently without tilting

After two hours of incubation, tilt the tube six times to wet the entire strip

Allow the tube to remain slanted for 10 minutes with the liquid covering the strip

Examine the top portion of the strip for changes to light or dark blue (= positive)