What are the limitations of oxidase tests?

Limitations of oxidase tests: 

• Oxidase tests don’t provide confirmatory results. Additional biochemical tests must be performed for complete identification. 
• The reagents used are photosensitive and have been shown to auto-oxidize. To get accurate results, the reagents must be freshly prepared, preferably daily and no older than one week. 
• Fresh bacterial culture must be used to get accurate results. Bacteria from older cultures may give false negative results. 
• Testing must be carried out on pure culture or well-isolated colonies. 
• Older colonies produce weaker results. Colonies must be no older than 18 to 24 hours. 
• Using bacteria grown on media containing dyes may give aberrant results. 
• Reagent-soaked colonies need immediate subculture when performing the direct plate method or they will become non-viable quickly. 
• Bacteria grown on glucose-rich media show inhibited oxidase activity, resulting in false negative results. It is advisable to test colonies grown on nutrient agar or tryptic soy agar, which do not have excess sugar. 
• Platinum inoculation loops are recommended as iron or Nichrome may yield false-positive results. 
• The time taken for the development of color change must be precisely recorded for accurate results. Any color changes appearing after 20 seconds should be disregarded.