MALDI-TOF MS in Microbial Molecular Identification

In recent years, bacteriologists began to pay attention to the application of mass spectrometry in bacterial identification, especially matrix-assisted laser desorption ionization time of flight (MALDI-TOF). Compared with traditional phenotypic techniques or molecular biology, MALDI-TOF-MS is a fast, accurate, and economical method for the identification of complete bacteria. In addition, it allows the identification of bacteria directly from clinical samples, such as blood cultures. Creative Biolabs has unique R&D expertise to provide the highest quality custom services for live biotherapeutic product (LBP) development.

The Principle of MALDI-TOF MS

This technique quickly identifies bacterial species by measuring the molecular mass of proteins, many of which are ribosomal proteins. Analysis is performed on whole cells or crude bacterial extracts. MALDI-TOF MS requires the sample to pass through a crystallization stage in a matrix on an inert carrier. The crystal mixture is irradiated with a brief laser pulse desorbs and ionizes characteristic ions (MALDI). The ionized molecules are accelerated in an electric field and separated in a vacuum tube as a function of molecular weight. The time of flight (TOF) of each ion is measured and corresponds to the time it takes to reach the detector. Depending on the m/z ratio of the ions, the ions arrive at the detector faster or slower. The electrical signal is processed by computer and converted into a mass spectrum.

Technical description of MALDI-TOF MS.Fig.1 Technical description of MALDI-TOF MS. (Croxatto, 2012)

MALDI-TOF MS: An Efficient Tool in Bacterial Species Identification

MALDI-TOF mass spectrometry: an efficient tool in bacterial species identification. In fact, when analyzing the microbial content of the human gut, MALDI-TOF MS assisted in the fast identification of bacterial species and in filtering potential new species. Identification of MALDI-TOF is based on the following findings :(1) different microbes have different spectral fingerprints, (2) some peaks (molecular weight) are specific to genera, species, and sometimes subspecies among the compounds detected in the spectra, and (3) the obtained spectra are repeatable as long as the bacteria are grown under the same conditions. MALDI-TOF-MS is based on the analysis of phenotypic traits that vary with medium and culture time. It can identify microorganisms at the species level and sometimes at the subspecies level.

Workflow of MALDI-TOF MS

To achieve rapid, accurate, simple, and reliable microbial identification, the new MS system is designed with highly automated operational and analytical processes. The majority of bacterial samples are separated and grown on a solid agar medium, and a single colony is then selected and smeared directly as a thin film on a MALDI target. A matrix solution (typically CHCA dissolved in acetonitrile) is then applied to the cells. However, Mycobacterium spp. and filamentous fungi usually require multi-step extraction methods to ensure the quality of biological proteome, thus improving the reliability of spectroscopy and identification.

Workflow for microbial identification using MALDI-TOF MS.Fig.2 Workflow for microbial identification using MALDI-TOF MS. (Jang, 2018)

Mass spectrometry fingerprint detection has become a convenient tool for rapid bacterial analysis. MALDI-TOF MS will soon replace automated and other phenotypic techniques as a widely used technique for routine clinical laboratory bacterial identification. Creative Biolabs is highly qualified with extensive experience and exceptional skills in the fields of microbial identification. Our goal is to provide our customers with affordable services with reliable results. If you are interested in our services, please contact us for more detail.

References

  1. Croxatto, A.; et al. Applications of MALDI-TOF mass spectrometry in clinical diagnostic microbiolog. FEMS microbiology reviews. 2012, 36(2): 380-407.
  2. Jang, K.S.; Kim, Y.H. Rapid and robust MALDI-TOF MS techniques for microbial identification: a brief overview of their diverse applications. Journal of Microbiology. 2018, 56(4): 209-216.

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