Comparison of direct smear and chemical extraction methods for MALDI-TOF mass spectrometry identification of clinical relevant anaerobic bacteria

Abstract

BackgroundThe Bruker Biotyper MALDI-TOF MS (Biotyper) system was evaluated for identification of anaerobic bacteria by chemical extraction and the direct smear technique. MethodA total of 216 strains of anaerobic bacteria representing 36 species were analyzed by two methods. 16S rDNA sequence analysis was used to resolve discrepancies. ResultsThe results showed that 202/216 (93.5%) strains were correctly identified following chemical extraction, among them, 176 strains (81.5%) were secured to both genus and species (score>2.00); another 26 strains (12%) were secured to genus only (score between 1.70 and 2.00). Following direct smear, 194/216 (89.8%) anaerobic bacteria were identified, 155 strains (71.7%) were secured to both genus and species (score)>2.0 whereas 39 (18%) strains were identified to genus only (score between 1.70 and 2.00). Fourteen strains were not identified (score<1.70) by MALDI-TOF MS following chemical extraction whereas 22 strains were not identified with the direct smear technique. Although direct smear had a less isolate number for score values>2.00, However the overall identification differences were not statistically significant (0.05<P<0.1). ConclusionMALDI-TOF MS identification following the direct smear technique appears to be non-inferior to standard chemical extraction. It may be an acceptable alternative to chemical extraction methods for routine identification of anaerobic bacteria in a medical microbiology laboratory.