Utility of MALDI-TOF MS in the rapid identification of mycobacteria

Background: In routine clinical laboratory diagnosis, characterizing a Mycobacterial isolate and its drug susceptibility is a tedious process, largely owing to its slow growth.Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a revolutionary technique which can be applied for the routine identification of Mycobacteria.Methods: In this prospective and blinded study, we attempted to characterize 100 clinical isolates of Mycobacteria using the MALDI-TOF and evaluate its utility as a useful tool for rapid identification of clinical Mycobacterial isolates.Fresh cultures (less than 7 days) of 100 (characterized to genus level) Mycobacterial isolates, grown either on Lowenstein Jensen slants or in the Bact/Alert MP bottles, were used.The isolates were initially disrupted with ethanol and silica beads.Acetonitrile & formamide acid extraction procedure was carried out and the supernatant was spotted on the target plate and Cinnamic acid was added.The plates were subjected to identification by MALDI-TOF MS.The spectra were acquired manually and recorded in the linear positive mode at a laser frequency of 20 Hz within a mass range from 2000 to 20,000 Da.The results of identification by MALDI were compared with the results from conventional techniques.Results: Among the 100 isolates, 80 were identified as Mycobacterium tuberculosis (M.tb) / bovis complex and 20 were non TB Mycobacteria (NTMs).There was a 100% correlation between the conventional and MALDI TOF results.The latter could identify the NTMs to the species level.Conclusion: This study showed that the MALDI-TOF MS was found to be an accurate, rapid and robust system for identification and differentiation of Mycobacteria.This innovative approach holds promise as an alternate and competent tool in mycobacteriology and helps in initiation of timely and appropriate therapeutic intervention.