The Microbial Identification MIDI system is based on which method?

• A. Antibiograms
• B. Colony pigment on ChromAgar
• C. Fatty acid analysis
• D. Multiple biochemical tests

Answer: (C)

The MIDI system identifies microbes by comparing their cellular fatty acid composition. It analyzes the fatty acids present in the organism’s membrane, typically after derivatization to fatty acid methyl esters, using gas chromatography. The resulting profile—a pattern of peaks representing the relative amounts of various fatty acids—acts as a chemical fingerprint that is matched against a reference library to determine the organism’s identity. This approach depends on standardized growth conditions because fatty acid profiles change with culture conditions, so consistent media and incubation are important. It’s different from antibiotic susceptibility tests, pigment-based colony appearance, or broader biochemical test panels, which rely on responses or phenotypes rather than direct chemical profiling of fatty acids.