Use of MALDI-TOF in the diagnosis of infectious diseases

1. Use ofMALDI-TOF in the diagnosis ofinfectious diseases
1. In this presentation the following papers have been used and these references and are
recommended for additional information
2. Clinical microbiology asa well-organized diagnostic profession has experienced a complete and
unexpected change by introducing the MALDI-TOF MS. Today everyone agrees that the
method of MALDI-TOF MS, a technology that is less than 30 years old, has revolutionized
clinical microbiology.
Almost the whole century bacterialidentification need more than 24 hours and the whole process
from sampling till presenting the finding to clinicians need 2 or 3 days (in some cases even
more). Matrix-assisted laser desorption ionization time-of-flight MS (MALDI-TOF MS) has
drastically improved the time to identification of a positive culture – only a few minutes are
needed.So, the whole processimproved dramatically. Together with some other novel methods,
such as molecular technology the time from sampling to results of diagnostic process are
shortened to just a few hours or in a worst case one day.
The role of mass spectrometry methods is not just in identification but typing as well, which is
shown in this illustration.
3. Identification of microorganism relies on different methods: Conventional detection of
phenotypic characteristics which includes Gram stain, and colony morphology
Morphology, microscopic examination, differential growth on selective media and various
biochemical tests
Using manual or automated methods
Molecular diagnostic methods including
16S ribosomal RNA sequencing and real-
time PCR detection of selected genes
The common characteristics of different molecular method is that they are complicated and
costly
And as stated the revolutionary technology - MALDI-TOF MS
4. MALDI-TOF MS: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry
– has many Advantages
- Implementation in a clinical microbiology laboratory is easy
- It has great Performance in bacterial identification with routine samples:
>90% - efficient and it is
- Reliable method for the identification of bacteria from clinical samples - It is Cost-effective:
At least ¼ of the price of conventional methods
(€2.44 with MALDITOF MS vs. €4.60–13.85 with an automated identification
- It is fast comaparing conventional methods
6 min versus hours or even days at sam identificaions level -
And even can be used in purpose of antimicrobial stewardship:
Together with local antibiotic resistance data

2. Efficiently optimize early empirical antibiotic treatment
5. The whole Workflow of MALDI-TOFMS is very simple: on one sample plate different samples
or multiple parallel direct depositions for the same sample might be performed in same time. In
a case of non- valid or doubtful results separate protein extractions might be done.
6. In short, after incubation, cultured colonies are applied directly to the test plate. The next step
is application of matrix which is a saturated solution of low-mass, acidic organic compounds
shuch as sinapinic acid - samples are overlaid with matrix. The next step is drying. After drying,
the prepared plate is loaded into the MALDI-TOF MS analyzer with software associated with
the system which enables fast identification.
7. So, the prepared sample plate, a metal carrier, is placed in the instrument, and brief laser pulses
hit the analyte (mixture of investigated colony and acidic matrix). The small desorbed and
ionized molecules are accelerated through an electrostatic field and drift through a fieldfree
tunnel until they reach the mass spectrometer’s detector. Molecules of different masses and
Charges will ‘fly’ at different speeds (hence the term ‘time-of-flight’). The result is a spectral
signature, with spikes generally in the range of 1000–20 000 m/z (mass-to-charge ratio). This
signature is then searched for in the appropriate database for the identification of the organism
to the genus or species level, according to values determined by the provider of the database.
8. The power of MALDI TOF MS are shown in specific species studies which gave nearly 100%
correct identifications of many bacterial species such as Neisseria, Clostridia, Mycobacteria,
Nonfermenters, Salmonella etc. And Yeasts (96% of 250 clinical Candida isolate) so there is
theoretically no limit to the identification ability although in some cases such as filamentous
fungi and dermatophytes because of their unique growth characteristics and morphology further
improvements in databases and pre-analytical protocols are needed
9. Another superior application of MALDI TOF MS versus conventional microbiology technique
is direct identification of pathogens in the sample itself, without a culture step which gave 66-
90 % of correct identification. This makes MALDI tof MS a promising tool in early start of
empirical antimicrobial therapy because of further shortening of identification time.
10. The weakest part of this technology is antibiotic susceptibility testing which is in development
and there is successes in ability to distinguish methicillin-susceptible S. Aureus from
methicillinresistant S. Aureus
Detection of various bacterial targeting antimicrobial molecules (such as b-lactamases,
methylases and efflux pumps) and detection of some other major virulence factors such as
Panton–Valentine leukocidin with a sensitivity of 100% and specificity of 90.6%
11. Also, another application of MALDI tof MS technology is in genotyping - MALDI-RE
(SEQUENOM) and electrospray ionization mass spectrometry (ESI-MS) MS methods are used
to analyse amplification products of PCR,and allowing precise typing of bacteria, comparable
with other molecular method such as multilocus sequence typing (MLST)
12. Nevertheless, this technology reveals many thing and open horizons and during the time of its
integration in routine practice there was different moments from high expectations to falls but
there are perfectly clear that MALDI TOF MS is revolution inside clinical microbiology

3. laboratory, a technology of today which provides rapid and fast identification of almost all
microbial pathogens, it is easy to use and low cost method.