[Identification of mycobacteria by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry--using reference strains and clinical isolates of Mycobacterium].

PURPOSE AND METHODS

Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) method is being played an important role for the inspection of clinical microorganism as a rapid and the price reduction. Mass spectra obtained by measuring become points of identification whether the peak pattern match any species mass spectral pattern. We currently use MALDI-TOF MS for rapid and accurate diagnosis of inactivated reference and clinical isolates of Mycobacterium because of the improved pretreatment techniques compared with former inspection methods that pose a higher risk of infection to the operator. The identification matching rate of score value (SV) peak pattern spectra was compared with that of conventional methods such as strain diffusion/amplification. Also, cultures were examined after a fixed number of days. Compared with the initial inspection technique, the pretreatment stage of current MALDI-TOF MS inspection techniques can improve the analysis of inactivated acid-fast bacteria that are often used as inspection criteria strains of clinical isolates. Next, we compared the concordance rate for identification between MALDI-TOF MS and conventional methods such as diffusion/amplification by comparison of peak pattern spectra and evaluated SV spectra to identify differences in the culture media after the retention period.

RESULTS AND DISCUSSION

In examination of 158 strains of clinical isolated Mycobacterium tuberculosis complex (MTC), the identification coincidence rate in the genus level in a matching pattern was 99.4%, when the species level was included 94.9%. About 37 strains of nontuberculous mycobacteria (NTM), the identification coincidence rate in the genus level was 94.6%. M. bovis BCG (Tokyo strain) in the reference strain was judged by the matching pattern to be MTC, and it suggested that they are M. tuberculosis and affinity species with high DNA homology. Nontuberculous mycobacterial M. gordonae strain JATA 33-01 shared peak pattern spectra, excluding the isolates, with each clinically isolated strain. However, the mass spectra of six M. gordonae clinical isolates suggested polymorphisms with similar mass-to-charge ratios compared with those of the reference strains. The peak pattern spectra of the clinical isolates and reference strains, excluding the NTM M. gordonae strain JATA33-01, were consistent with the peak pattern characteristics of each isolate. However, a comparison between the peak patterns of the reference strains and those of the six clinically isolated M. gordonae strains revealed a similar mass-to-charge ratio, which may indicate few polymorphisms. The SV spectrum of the improved inspection technique showed no fidelity, but it was acceptable after days of culture as indicated by the decrease in SV (0.3 degree). Also, the reproducibility of this method was good, but no difference was observed from the SV of the improved inspection technique, which decreased by approximately 0.3 because of the number of days of culture storage. In addition, expansion of the database and dissemination of regional specificity by genotype analysis of clinical isolates was relevant to the accumulated data, as expected. In future studies, the relevance and regional specificity of clinical isolates by genotype analysis can be determined by stacking the solid media and database penetration.