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  Table of Contents  
COMMENTARY
Year : 2014  |  Volume : 32  |  Issue : 4  |  Page : 423-424
 

MALDI-TOF MS for rapid identification of clinically relevant bacterial and fungal isolates


Department of Microbiology, Dr. Pinnamaneni Siddhartha Institute of Medical Sciences and Research Foundation, Chinoutpalli, Gannavaram Mandal, Krishna, Andhra Pradesh, India

Date of Web Publication4-Oct-2014

Correspondence Address:
C R Setty
Department of Microbiology, Dr. Pinnamaneni Siddhartha Institute of Medical Sciences and Research Foundation, Chinoutpalli, Gannavaram Mandal, Krishna, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


PMID: 25297029

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How to cite this article:
Setty C R. MALDI-TOF MS for rapid identification of clinically relevant bacterial and fungal isolates . Indian J Med Microbiol 2014;32:423-4

How to cite this URL:
Setty C R. MALDI-TOF MS for rapid identification of clinically relevant bacterial and fungal isolates . Indian J Med Microbiol [serial online] 2014 [cited 2019 Nov 17];32:423-4. Available from: http://www.ijmm.org/text.asp?2014/32/4/423/142260


Dear Editor,

All clinical microbiology laboratories wish to bring down the turnaround time as much as possible, at the same time maintaining accuracy and quality. [1] Many traditional culture-based methods take at least 24 h for identification after isolation of the microorganism. To reduce this time, so that the clinician and thus the patient get benefit for early and accurate diagnosis and treatment, many attempts were made. The rapid tests like the spot tests like indole, oxidase, etc., the semi automated tests like API panels, sceptor, enterotube and the automated systems like Phoenix, MicroScan Walkaway and Vitek are in this direction. However all these developments still need about 16 h to get identification itself after isolation of the organism. While these developments have given significant contribution towards accuracy and to some extent rapidity in identification, still limitations exist. Newer approaches of utilising developments in molecular techniques for bacterial identification like DNA sequencing, real time polymerase chain reaction (RT-PCR) and peptide nucleic acid-fluorescent in situ hybridisation have helped in reducing turnaround time.

Matrix-assisted laser desorption/ionisation-Time of fl ight Mass spectrometry (MALDI-TOF MS) is an ionisation technique where biological molecules like proteins, DNA, etc., and large organic molecules like polymers are analysed using mass spectrometry. [2] The biomolecules are fragile and fragment when ionised by conventional ionisation methods. MALDI and electro spray are two techniques for obtaining large molecules into gas phase without fragmenting these biomolecules. Thus they are called soft ionisation processes. It is a two step process. Initially the desorption and ionisation take place triggered by an ultraviolet (UV) laser beam followed by measurement of the mass/charge ratio of the resulting ions of the biomolecules. The sample to be analysed is mixed with a large quantity of matrix and placed onto MALDI plate, which is a metal plate specially designed for this purpose. A laser is passed on to this spot of matrix, which absorbs the laser energy and converts it to heat energy. Due to this heat energy, a small portion of matrix (up to about 100 nm from the top) heats up rapidly in nanoseconds and gets vaporised along with the sample. During this process, the matrix absorbs laser energy and gets ionised. The matrix then transfers the protons to the analyte thereby ionising the analyte as well. These ions are separated based on mass/charge ratio in the time of flight (TOF) analyser. The smaller ions of lower m/z travel faster and reach the instrument's detector earlier than larger ions of higher m/z. The resulting pattern is compared with the known data of yeasts and bacteria in the test system database to identify the pathogen. This procedure requires only a small amount of yeast or bacterial growth and so testing can start as soon as the growth is visible, generally within 18-24 h. The authors in this issue's article "Use of MALDI-TOF MS technique for rapid identification of bacteria from positive blood culture", however, were able to work on the growth within 4-6 hours itself and got results correlating to 80.6 - 90.9% thereby reducing the identification time significantly. However, it is to be used as always, along with other clinical [1] and laboratory findings as an aid for diagnosis of bacterial and fungal infections.

This approach in spite of having the potential to reduce the turnaround time still has limitations. This procedure is not applicable to specimens directly. So the necessity to have initial culture is one of the limitations. The use of automated blood culture systems like Bact/Alert and Bactec have benefited the microbiology laboratories when dealing with blood and sterile body fluids in reducing the times for getting the inital growth. However the main hurdle of determining the antibiogram still remains since the new MALDI-TOF MS cannot provide simultaneous antibiogram. This is the place where antibiotic stewardship comes in. Thus this new technique holds promise for rapid and accurate identification of bacteria and fungi though it has limitation on antibiogram. Further the initial and running costs, work load, type of patients and working environment whether it is a tertiary care centre or not would be the guiding factors in opting such a technology for laboratories. There are studies evaluating the identification accuracy and time on clinically relevant isolates. [3],[4]

Bruker Biotyper (microflex-LT) and VITEK MS are two instruments, which use the above principle for identification of microorganisms. [5] The US food and Drug Administration has approved the VITEK MS for the purpose of automated identification of bacteria and yeasts in August 2013. The system can identify 193 different microorganisms and can perform up to 192 different tests in a single automated series of testing, with each test taking about 1 min. [6]

 
 ~ References Top

1.Hong SK, Chang BK, Song SH, Kim EC. Use of MALDI-TOF MS technique for rapid identification of bacteria from positive blood culture. Indian J Med Microbiol 2014:34:419-24.   Back to cited text no. 1
    
2.Caprioli RM, Farmer RB, Gile J. Molecular imaging of biological samples: Localization of peptides and proteins using MALDI-TOF MS. Anal Chem 1997;69:4751-60.  Back to cited text no. 2
    
3.Tan KE, Ellis BC, Lee R, Stamper PD, Zhang SX, Carroll KC. Prospective evaluation of a matrix-assisted laser desorption ionization-time of flight mass spectrometry system in a hospital clinical microbiology laboratory for identification of bacteria and yeasts: A bench-by-bench study for assessing the impact on time to identification and cost-effectiveness. J Clin Microbiol 2012;50:3301-8.  Back to cited text no. 3
    
4.Ford BA, Burnham CA. Optimization of routine identification of clinically relevant Gram-negative bacteria by use of matrix-assisted laser desorption ionization-time of flight mass spectrometry and the Bruker Biotyper. Clin Microbiol 2013;51:1412-20.  Back to cited text no. 4
    
5.Marko DC, Saffert RT, Cunningham SA, Hyman J, Walsh J, Arbefeville S, et al. Evaluation of the Bruker Biotyper and Vitek MS matrix-assisted laser desorption ionization-time of flight mass spectrometry systems for identification of nonfermenting gram-negative bacilli isolated from cultures from cystic fibrosis patients. J Clin Microbiol 2012;50:2034-9.  Back to cited text no. 5
    
6.New test system identifies 193 different yeasts and bacteria known to cause illness. FDA press release:2013. www.fda.gov/newsevents/newsroom/pressannouncements/ucm365907  Back to cited text no. 6
    




 

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