title: Chemical extraction versus direct smear for MALDI-TOF mass spectrometry identification of anaerobic bacteria.
abstract: In the present study, two pre-analytic processes for mass spectrometric bacterial identification were compared: the time-consuming reference method, chemical extraction, and the direct smear technique directly using cultured colonies without any further preparation. These pre-analytic processes were compared in the identification of a total of 238 strains of anaerobic bacteria representing 34 species. The results showed that 218/238 strains were identified following chemical extraction, 185 identifications (77.7%) were secured to both genus and species [log(score) > 2.0] whereas 33 identifications (14%) were secured to genus only [log(score) between 1.7 and 2.0]. Following direct smear, 207/238 anaerobic bacteria were identified, 158 identifications (66.4%) were secured to both genus and species [log(score) > 2.0] whereas 49 identifications were secured to genus only [log(score) between 1.7 and 2.0]. Twenty strains were not identified [log(score) < 1.7] by MALDI-TOF MS following chemical extraction whereas 31 strains were not identified with the direct smear technique. Although direct smear led to a significant decrease of the log(score) values for the Clostridium genus and the Gram positive anaerobic bacteria (GPAC) group (p < 0.0001, Wilcoxon test), identification to both species and genus were not changed. However these differences were not statistically significant (p = 0.1, Chi square). Therefore, MALDI-TOF MS identification following the direct smear technique appears to both non-inferior to the reference method and relevant for anaerobic bacteria identification.
authors.affiliation: Laboratoire de Bactériologie Hygiène, CHU Lille, France.
authors.forename: Rémi
authors.initials: R
authors.lastname: Fournier
authors.forename: Frédéric
authors.initials: F
authors.lastname: Wallet
authors.forename: Bruno
authors.initials: B
authors.lastname: Grandbastien
authors.forename: Luc
authors.initials: L
authors.lastname: Dubreuil
authors.forename: René
authors.initials: R
authors.lastname: Courcol
authors.forename: Christel
authors.initials: C
authors.lastname: Neut
authors.forename: Rodrigue
authors.initials: R
authors.lastname: Dessein
mesh_terms: D001421:Bacteria, Anaerobic / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D055442:Metabolome; D058889:Molecular Typing; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S