Date Published: July 3, 2019
Publisher: Public Library of Science
Author(s): María Florencia Rocca, Rubén Barrios, Jonathan Zintgraff, Claudia Martínez, Lucía Irazu, Carlos Vay, Mónica Prieto, Joseph Banoub.
Mass spectrometry has revolutionized the clinical microbiology field in America’s and Europe’s industrialized countries, for being a fast, reliable and inexpensive technique. Our study is based on the comparison of the performance of two commercial platforms, Microflex LT (Bruker Daltonics, Bremen, Germany) and Vitek MS (bioMérieux, Marcy l´Etoile, France) for the identification of unusual and hard-to-diagnose microorganisms in a Reference Laboratory in Argentina. During a four-month period (February–May 2018) the diagnostic efficiency and the concordance between both systems were assessed, and the results were compared with the polyphasic taxonomic identification of all isolates. The study included 265 isolates: 77 Gram-Negative Bacilli, 33 Gram-Positive Cocci, 40 Anaerobes, 35 Actinomycetales, 19 Fastidious Microorganisms and 61 Gram-Positive Bacilli. All procedures were practiced according to the manufacturer’s recommendations in each case by duplicate, and strictly in parallel. Other relevant factors, such as the utility of the recommended extraction protocols, reagent stability and connectivity were also evaluated. Both systems correctly identified the majority of the isolates to species and complex level (82%, 217/265). Vitex MS achieved a higher number of correct species-level identifications between the gram-positive microorganisms; however, it presented greater difficulty in the identification of non-fermenting bacilli and a higher number of incorrect identifications when the profile of the microorganism was not represented in the commercial database. Both platforms showed an excellent performance on the identification of anaerobic bacteria and fastidious species. Both systems enabled the fast and reliable identification of most of the tested isolates and were shown to be very practical for the user.
Traditionally, the bacterial and fungal identification from clinical samples has been based on the observation and analysis of microscopic, cultural, and metabolic characteristics through the use of special stains, conventional biochemical tests , miniaturized galleries and automated methods. These are laborious procedures that can require a long time to reach a definite result. This has a direct impact on the therapeutic and epidemiological aspects, for it is known that the earlier and more appropriate the antimicrobial treatment is, the lower the patients mortality will be, especially for the ones that are in a serious condition. Nowadays, the gold-standard method for the bacteria that cannot be identified by traditional techniques is the genomic analysis. However, this methodology can be costly and tends to be difficult to implement in a conventional microbiology laboratory [2–4].
The study was conducted between February and May 2018 in the Special Bacteriology Laboratory within the National Reference Institute INEI-ANLIS “Dr Carlos G. Malbrán”. Buenos Aires, Argentina.
The mass spectrometry results were compared with the identifications obtained by the gold-standard method and were classified as follows: correct species identification, correct genus identification, correct group or complex identification, NI. We recorded the cases in which the identification failure was due to the absence of a species protein profile in the DB and when the limitation in the identification had already been described by the manufacturers. Those cases in which it was not possible to obtain reproducible spectra (No Peaks result) in spite of testing different extraction methods, were also detailed.
Since the introduction of mass spectrometry, routine microbiological diagnosis has reached a new era; it provides faster and more reliable results and reduces the need of performing complex techniques that occupy personnel and adds costs to the laboratory. This is why a great number of health institutions throughout the world have incorporated this new technology; however, an important aspect that should be considered is the existence of two systems available in the market, and what their performance with spectra of local biological variants and South America’s laboratory infrastructure is like.
Both MALDI TOF systems showed a high performance and strength, being faster, more accurate and more economic than conventional biochemical tests or molecular techniques.