Background: Cystic Fibrosis (CF ) is an autosomal recessive disorder which affects a number of organ systems, most severely the lungs. Progression of lung disease is in part monitored by culture of certain respiratory pathogens. Organisms of most concern include the Burkholderia cepacia complex (Bcc). The Bcc consists of 17 closely related species, with specific clinical outcomes. Identification of the Bcc by phenotypic methods is difficult. We previously developed an improved method for Bcc identification by recA gene sequencing, and in this study we compare that method with MALDI-TOF MS.
Method: Unique isolates of Bcc from sputa of CF patients at Westmead Hospital from December 2011 to February 2013 were speciated by recA gene sequence analysis (10 patients). MALDI-TOF MS was performed following HCO2H extraction on 24hr cultures. Protein spectra were compared to the BrukerTM Biotyper MALDI-TOF database (version 3.1.66). Seven isolates collected from blood cultures (usually environmental contaminants) were also identified by recA sequence and MALDI-TOF MS.
Results: Three Bcc species were identified by recA in CF sputa; B. multivorans, B. cenocepacia and B. cepacia. All 10 isolates of these were correctly identified to the species level by MALDI-TOF (score value ≥2.0). A further 3 species were identified by recA in blood; B. stabilis, B. lata and B. contaminans. 6 of these 7 isolates were correctly identified by MALDI-TOF. A single isolate of B. contaminans misidentified as B. cepacia (Score value 2.247). B. contaminans is not included in the BrukerTM Biotyper MALDI-TOF database (version 3.1.66).
Conclusion: MALDI-TOF MS was a fast and useful alternative to our standard method of identification of commonly encountered species of the Bcc . 94% of isolates (16/17) representing seven species were identified. Further studies to evaluate the ability of MALDI-TOF MS to identify less common species of the Bcc are needed.