What precautions should I take during oxidase tests?

These are some of the recommended precautions you should be mindful of during oxidase tests: 

• Always use fresh bacterial culture and freshly-made oxidase reagent for your test.
• Make sure that your sample is obtained from well-isolated colonies. To ensure that your sample is sure, it is advisable to obtain cultures from selective media. If you’re working with a mixed culture, do not perform the direct plate technique. 
• When necessary, store oxidase reagent at – 20°C in a dark place. 
• Avoid testing bacteria grown on glucose-rich culture medium or media with dyes such as EMB or MAC medium. 
• Use only as much oxidase reagent as necessary on the plate. Avoid over-flooding the plate with an oxidase reagent. 
• Avoid using nichrome wire loops, as they often tend to produce false-positive results. 
• Avoid testing strict anaerobes. 
• Be precise when recording time to distinguish between rapid oxidase-positive bacteria, delayed oxidase-positive bacteria, and oxidase-negative bacteria. 
• When using Kovacs reagent, make sure to record the result within 60 seconds. When using Gaby-Hadley Reagents, the result must be recorded within 3 minutes.