|513-1||Speciation of Environmental Enterococci Isolates through MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time of Flight) Mass Spectrometry Analysis|
|Autores:||Ana Paula Guarnieri Christ (CETESB - Companhia Ambiental de São Paulo) ; Solange Ramos (CETESB - Companhia Ambiental de São Paulo) ; Rodrigo Cayô (UNIFESP - Universidade Federal de São Paulo) ; Ana Cristina Gales (UNIFESP - Universidade Federal de São Paulo) ; Elayse Maria Hachich (CETESB - Companhia Ambiental de São Paulo) ; Maria Inês Zanoli Sato (CETESB - Companhia Ambiental de São Paulo) |
Introduction:In recent years a new approach to identify microorganisms based on mass spectrometric analysis had been proposed. MALDI-TOF MS (Matrix-assisted laser desorption/ionization – Time of Flight Mass Spectrometry) is a powerful method for the detection and identification of proteins by molecular weight determination of specific fragments. Bacterial identification by MALDI-TOF analysis is based on the detection of the mass spectral fingerprint obtained from the whole cell. The method is becoming widely used for the identification of clinically important microorganisms and now this approach is being tested in the environmental microbiology field. Methods:This study aimed to compare the identification efficiency of the biochemical test API® 20 STREP, which is the currently gold standard identification system for Enterococci strains in our laboratory, with the MALDI-TOF MS. Water samples from 7 beaches were collected during 4 weeks and processed by membrane-filtering technique. 127 bacterial isolates presumptively identified as enterococci on mEI media were speciated both, by the MALDI TOF Bruker Microflex apparatus and by conventional identification API system from bioMérieux. Results:API® system was able to identify 117 out of 127 strains (92%) whereas MALDI-TOF analysis returned positive results for 100% of the isolates. To the genus level, all the 111 bacterial isolates that were identified as Enterococcus by the API test, had the agreement with the MALDI-TOF system. However, to the species level only 63% of the isolates granted the same identification with both systems. API® system identified the 111 Enterococcus strains as being 71% E. faecium, 12% E. faecalis and 17% E. durans. By its time, MALDI-TOF analyses were able to identify 117 out of the127 isolates as belonging to the Enterococcus genus with the following distribution: 58% E. faecium, 18% E. faecalis. 15% E. hirae, 5% E. casseliflavus, 2,5% E. gallinarum and 1% E. munditti. Conclusion:MALDI-TOF MS demonstrated great accuracy and specificity to identify Enterococci environmental strains. Moreover, compared to API system, MALDI-TOF demonstrated a greater resolution to identify Enterococcus strains. Since speciation of Enterococcus isolates can differentiate plant-associated from fecal-associated species, this technique could represent a useful tool for microbial source tracking purposes.
Palavras-chave: Enterococcus, Speciation, MALDI-TOF, API System