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

Background

The Bruker Biotyper MALDI-TOF MS (Biotyper) system was evaluated for identification of anaerobic bacteria by chemical extraction and the direct smear technique.

Method

A total of 216 strains of anaerobic bacteria representing 36 species were analyzed by two methods. 16S rDNA sequence analysis was used to resolve discrepancies.

Results

The 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).

Conclusion

MALDI-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.