Background: The use of MALDI-TOF has been successfully implemented for rapid identification of bacteria in clinical laboratories. Conversely, identification of mycobacteria is more cumbersome, due to the unique bacterial wall and slow growth. A recently FDA approved procedure for identification of mycobacteria and Nocardia was introducred by BioMerieux. We evaluated mycobacteria identification using Vitek® MS (bioMérieux mass spectrometry) with a wide range of species commonly found in the routine TB laboratory.
Materials/methods: Mycobacteria collected from long term stored isolates (N=23), new positive sputum samples (N=16) and external quality-control CAP samples (N=10) were processed as depicted in the scheme below. In short, incubation in MGIT liquid media (Becton Dickenson, USA) & Lowenstein Johnson solid media (LJ; Novamed Ltd. Israel), followed by verification of acid fast bacteria presence (AFB+), subcultures on TSA-blood and L.J. cultures, were carried out. Final identification was determined by Vitek® MS using Vitek® MS Mycobacterium/Nocardia kit and PCR using GenoType mycobacterium CM kit (Hein, Germany).
Results: The MS technology successfully identified 43 isolates grown on L.J. and TSA-blood cultures. The remaining 6 isolates either did not grew on subculture (N=3); grew contaminated (N=1) or were identified as non-mycobacteria (N=2). The successfully identified species included: M.intracellulare (N=13); M.simiae (N=7); MTBC (N=4); M. gordonae, M.avium, M.fortuitum & M.kansasii (N=3, each); M.abscessus (N=2); M.chelonae, M.scrofulaceum, M.xenopi, Nocardia & M.asiaticum (N=1, each). Isolated colonies from TSA-blood and L.J. cultures were identified using the Vitek® MS in equal accuracy and 99% confidence level. TSA-blood cultures required 2-5 days incubation (3.5 days average) for sufficient colony growth, vs. L.J cultures which required 12-36 days incubation (24 days average).
Conclusions: The mycobacteria isolates tested were accurately identified by the Vitek® MS with high confidence. Vitek® MS was found to be superior in comparison to the molecular method in many aspects: wide data-base enabling identification of 48 isolates, less colonies needed for identification, results received automatically with no need for subjective interpretation, reduced time to result, hands-on-time and reagent costs reduced by more than 50%. Furthermore, colonies isolated from TSA-blood cultures were appropriate for use, thus reducing incubation stage significantly.