No identification method dominates on every axis, and the laboratory's choice depends on what the clinical situation demands. A conventional biochemical panel is inexpensive and needs no specialized instrument, but it depends on growth and typically takes 18 to 24 hours. Rapid chromogenic and enzyme-substrate tests cut that to hours by detecting preformed enzymes, at the cost of a narrower range and a presumptive rather than definitive result. Antigen tests are fast and can work directly on body fluid, but each test answers only one question. MALDI-TOF is fast, cheap per test, and broad within its library, but it requires a pure viable colony and a reference library that contains the organism. Automated panels standardize the whole process and reduce technical variation, yet they inherit the same dependence on isolate quality and database completeness.
The practical rule is to match the method to the decision. When a result is needed within hours and the organism is already suspected, a rapid or antigen test may be sufficient. When a broad, definitive identification is needed and the organism is growing on a plate, MALDI-TOF is usually the first choice. When the organism is unusual or absent from the library, the laboratory must fall back on conventional biochemical testing or, as a later chapter covers, molecular methods.