304 COMMENTARY ( see article on p . 378 )
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Advances in dermatology and venereology Acta Dermato-Venereologica
Matrix-Assisted Laser Desorption / Ionisation Time-Of-Flight Mass Spectrometry in Dermatology
David CHANDLER 1 and Roderick HAY 2
1
Charing Cross Hospital , Imperial College NHS Trust , and 2 Kings College , London , United Kingdom . E-mail : roderick . hay @ ifd . org
Until recently the laboratory diagnosis of infections has depended on the use of cultural identification , often coupled with biochemical tests . Increasingly , this process has been changed and refined with the development of rapid and accurate molecular methods . Most attention has focused on the detection of identifying genetic material , RNA or DNA ; nucleic acid amplification techniques provide a rapid and sensitive method for microbial detection . However a new approach using Matrix-Assisted Laser Desorption / Ionisation Time-Of-Flight ( MALDI-TOF ) Mass Spectrometry ( MS ) has emerged as a powerful tool for microbial identification and research . Mass spectrometry involves the ionisation of chemical compounds into charged molecules and measurement of their mass to charge ( m / z ) ratio . The development of ‘ soft ionisation ’ methods such as MALDI has widened the application of MS to the detection of large biological molecules , including polypeptides , glycoproteins and complex carbohydrates . The process involves mixing the microbiological sample with an energy-absorbent matrix ; constituents are ionised by laser energy and separated , based on the time taken to travel along a flight tube that depends on their mass-to-charge ratio . These data are used to construct a mass spectrum or peptide mass fingerprint ( PMF ) that is compared against a database of reference spectra , identifying the organism to genus , species or strain level . Highly abundant microbial proteins , mostly ribosomal proteins in the mass range 2-20 kDa , are the main contributors to the PMF for an individual organism and results can be generated in seconds and with a minimum of material .
MALDI-TOF MS is a sensitive and very rapid technique for analysing a wide range of microbial products . In addition to the identification of organisms it can provide useful information , for instance , on antibiotic susceptibility , through the detection of resistance-associated proteins ( e . g . beta-lactamases ). The potential for rapid , high-throughput analysis of protein products from complex mixtures makes MALDI-TOF MS an important technology in studying pathogenetic mechanisms . It can also be used to image proteins directly from intact tissue sections , a process known as imaging mass spectrometry ( IMS ). This can provide information on the relative concentration and spatial distribution of proteins within different areas of tissue ( healthy and diseased ). It is a cost-effective method for microbial detection , compared with molecular and immunological methods , however high setup costs may be a barrier to initial implementation and sometimes there can be difficulty in distinguishing genetically very similar organisms .
The literature contains many examples of the benefits of using MALDI-TOF MS , for both clinical diagnosis and as a research tool in dermatology . The accurate classification of strains of Propionibacterium acnes at the proteomic level has provided a foundation for further molecular investigation to characterise the role of this organism in the pathogenesis of acne ( 1 , 2 ). Numerous case reports highlight the utility of MALDI-TOF MS ( often supported by DNA / RNA sequencing ) in the identification of new and rare organisms in clinical specimens , which might not otherwise be detected using conventional methods . Baran et al . ( 3 ) recently described a case of chronic lower leg wound infection with Kerstersia gyiorum ( diagnosed by MALDI-TOF MS ) in a patient with Buerger ’ s disease . They draw attention to the likelihood of misdiagnosis of this organism using biochemical methods in isolation . The use of this technique is not restricted to bacteria and is finding wide acceptance as a rapid method for identifying fungi such as dermatophytes and yeasts isolated from clinical material ( 4 , 5 ).
In this issue Del Giudice and colleagues ( 6 ) report the first case of cellulitis caused by an emerging pathogen , Streptococcus halichoeri . They highlight the usefulness of MALDI-TOF for microbial identification in comparison to conventional methods . Results obtained from microbiological samples using biochemical methods were discordant . Subsequent evaluation with MALDI-TOF mass spectrometry identified the organism as S . halichoeri . The use of MALDI-TOF MS in this case ( supported by 16S rRNA gene sequencing ) confirmed the cause of cellulitis .
The increasing use of modern molecular tools such as MALDI-TOF MS will result in the detection of more unusual and unfamiliar microorganisms ; but communication between clinicians and laboratory scientists will remain important in order to determine their pathogenic relevance as well as resistance patterns . Maintaining , and adding to , reference data bases where comparative information on the mass fingerprints is stored is key to the future success and application of this method .
REFERENCES
1 . Nagy E , Urbán E , Becker S , Kostrzewa M , Vörös A , Hunyadkürti J , Nagy I . MALDI-TOF MS fingerprinting facilitates rapid discrimination of phylotypes I , II and III of Propionibacterium acnes . Anaerobe 2013 ; 20 : 20 – 26 .
2 . Johnson T , Kang D , Barnard E , Li H . Strain-level differences in porphyrin production and regulation in Propionibacterium acnes elucidate disease associations . mSphere 2016 ; 1 / 1 . e00023-15 .
3 . Baran I , Düzgün AP , Mumcuoğlu I , Aksu N . Chronic lower extremity wound infection due to Kerstersia gyiorum in a patient with Buerger ’ s disease : a case report . BMC Infect Dis 2017 ; 17 : 608 .
4 . Packeu A , De Bel A , l ’ Ollivier C , Ranque S , Detandt M , Hendrickx M . Fast and accurate identification of dermatophytes by matrix-assisted laser desorption ionization-time of flight mass spectrometry : validation in the clinical laboratory . J Clin Microbiol 2014 ; 52 : 3440 – 3443 .
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This is an open access article under the CC BY-NC license . www . medicaljournals . se / acta Journal Compilation © 2018 Acta Dermato-Venereologica .