Samenvatting eindwerk 2014-2015: Validation and implementation of MALDI -TOF MS in a clinical microbiology lab
In the clinical microbiology laboratory of CRI the identification of bacteria is based on current methods, quick tests and selected media. These methods have some cons. The identification of bacteria takes very long. The methods needs many hours of incubation. A second disadvantage is the cost because there are many different tests required.
Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) offers the possibility of accurate, rapid, inexpensive identification of bacteria in clinical microbiology laboratory. This technique is an ionization method which allows desorption of proteins from different microorganisms. Ions will be separated and detected by their molecular mass. The bacteria are identified on the basis of the mass/charge ratio (m/z). This proceeds to a spectrum. This spectrum can be compared to a database. There will be an agreement between the measured spectrum and the reference spectrum. This is linked to the correct microorganism.
The validation results will be compared with American Type Culture Collection (ATCC) strains, Extern Quality Control (EQC) strains and routine germs.
A validation plan was worked out and containing the following criteria:
- Accuracy and reliability
- Effect of culture age on reliability
- Stability of germ on target covered or uncovered spots with matrix
- Formic acid extraction on yeasts
- Streptococcus species in a bacterial solution
All of the criteria of the MALDI-TOF method were good. The identification of bacteria and yeasts by MALDI-TOF MS proved to be extremely reliable and reproducible. But there are still some limitations noticed in our validation. These are very important in the daily operation of a routine microbiology lab. The two most important constrains are the Shigella limitation and the S. pneumoniae/mitis/oralis limitation. The efficacy of MALDI-TOF MS identification of Candida species appeared to be higher with the 70% formic acid extraction. So the formic acid extraction of yeast will be included as a standard procedure in the labprotocol. The bacterial solution of Streptococcus was not optimal. Further research is recommended.
As a final conclusion, we can conclude that the identification of bacteria and yeast with MALDI-TOF MS is a great progress in a clinical microbiology. The benefits are low cost, speed of execution, reliability and reproducibility.
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