[Applications of MALDI-TOF technology in clinical microbiology]

Instantaneous Response of Bacteria to External Stimuli Monitored by Syringe Spray Mass Spectrometry

Microbial adaptation to environmental stress involves complex adaptations of bacteria. Many such responses are transient and dynamic. However, monitoring the dynamic responses of live bacteria to stimulations at the molecular level remain a challenge. This work describes the development of syringe spray mass spectrometry (MS) method that allows direct analyses of molecules released by the bacteria in responses to external stimuli with second level time resolution. We report the application of this technique to visualize the dynamic release of small molecules from Escherichia coli ( E. coli) under ethanol and isopropanol treatments. With the unique time-resolved capability, detailed destruction process of alcohol on bacteria cell wall could be observed. Compared to other ethanol concentrations, 75% ethanol showed stronger damages to lipopolysaccharide (LPS) and peptidoglycan located on E. coli cell wall. Furthermore, isopropanol showed stronger liposolubility and permeability, and an equilibrium could be achieved in a much shorter time.

Rapid and safe one-step extraction method for the identification of Brucella strains at genus and species level by MALDI-TOF mass spectrometry

Brucellosis is essentially a disease of domesticated livestock; however, humans can also be infected via the consumption of contaminated meat or dairy products, underlying the need for rapid and accurate identification methods. Procedures for microbiological identification and typing of Brucella spp. are expensive, time-consuming, and must be conducted in biohazard containment facilities to minimize operator risk. The development of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS)-based assay has reduced the processing time while maintaining performance standards. In this study, to improve the identification accuracy and suitability of the MALDI-TOF-based assay for routine diagnosis, we developed a new protein extraction protocol and generated a custom reference database containing Brucella strains representative of the most widespread species. The reference library was then challenged with blind-coded field samples isolated from infected animals. The results indicated that the database could be used to correctly identify 99.5% and 97% of Brucella strains at the genus and species level, respectively, indicating that the performance of the assay was not affected by the different culture conditions used for microbial isolation. Moreover, the inactivated samples were stored and shipped to reference laboratories with no ill effect on protein stability, thus confirming the reliability of our method for routine diagnosis. Finally, we evaluated the epidemiological value of the protocol by comparing the clustering analysis results of Brucella melitensis strains obtained via multiple locus variable-number tandem repeat analysis or MALDI-TOF MS. The results showed that the MALDI-TOF assay could not decipher the true phylogenetic tree, suggesting that the protein profile did not correspond with the genetic evolution of Brucella.

Accuracy of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Mycobacteria: a systematic review and meta-analysis

Mycobacterium species are a significant cause of morbidity and mortality worldwide. The present study was carried out to systematically evaluate the accuracy of Matrix-assisted laser desorption ionization-time of flight mass spectroscopy (MALDI-TOF MS) for the identification of clinical pathogenic mycobacteria. After a rigid selection process, 19 articles involving 2,593 mycobacteria isolates were included. The pooled result agreed with the reference method identification for 85% of the isolates to genus level, with 71% (95% CI of 69% to 72%) correct to the species level. The MALDI-TOF MS correctly identified 92% of the M.tuberculosis isolates (95% CI of 0.87 to 0.96), and 68% of M. bovisisolates (95% CI of 27% to 100%) to the species level. Mycobacterium tuberculosis complex in solid media with reference strains using augmented database showing more accurate identification. The identifying accuracy rate of bioMérieuxVitek MS was slight higher than Bruker MALDI Biotyper (75% vs 72%). However, opposite results were obtained in identifications of M. fortuitum, M. kansasii, M. marinum, and M. terrae with these two systems. In summary, our results demonstrate that application of MALDI-TOF MS in clinical pathogenic mycobacteria identification is less satisfactory to date. Increasing need for improvement is important especially at species level.

MALDI-TOF MS Versus VITEK®2: Comparison of Systems for the Identification of Microorganisms Responsible for Bacteremia

We evaluated the reliability and accuracy of the combined use of MALDI-TOF MS and classical ID VITEK₂ to identify monomicrobial infection in blood culture bottles. In total, 70 consecutive positive blood cultures were included in this study. Positive blood culture bottles were subjected to Gram staining and subcultured on solid media. Isolates grown from such culture media were used for classical ID using VITEK₂ system. In parallel, an aliquot was subjected to a lysing-centrifugation method and used for the identification with the MALDI-TOF system. Results evidenced the correct genus and species identification of 91.4 % of microorganisms responsible for bacteremia with an agreement to the species and the genus level. If compared with the standard method VITEK₂, our simple and cost-effective sample preparation method would be very useful for rapid identification of microorganisms using blood culture bottles. In fact, the direct method showed rapid and reliable results, especially for the gram-negative group.