HPLC (high-performance liquid chromatography) (able to make a definitive ID)
- Used by referral, research, and public health laboratories to differentiate closely related species.
- Short-chain fatty acid products are measured.
- About an hour to perform a run.
- Useful and accurate but impractical for most medical laboratories.
MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry) (able to make a definitive ID)
- Rapid identification method comparing the mass spectrum of organisms with those of known reference strains.
- Automated.
- Very sensitive method, often considered superior. High degree of accuracy.
- Extremely popular in labs that can afford the initial cost of the instrument.
- A very small amount of biomass is required.
- Aerotolerance testing is required (but this requirement may change as the use of this method becomes more popular).14
- Identification may be made directly from the primary culture plate as long as colonies are well isolated and large enough to test.
- Very small colonies from mixed cultures may need subculturing before being set up on the MALDI-TOF MS platform.
- Databases are updated frequently; however, rare anaerobes may pose a challenge.
Sequencing (able to make a definitive ID)
- Gold standard for species identification.
- Specialized knowledge and equipment is required.
- Difficult to perform—usually reserved for reference, research, or public health laboratory.
Procedural note: As with any method, care must be taken to compare the identification obtained with the Gram stain and the body site of the infection. Always ask: "Does this make sense?"
