Role of Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry for Species Identification of Strains.

  species has become a leading cause of nosocomial infections in recent years.  The aim of the study was to establish the usefulness of matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) for the identification of species with respect to conventional biochemical methods and MicroScan WalkAway 96 Plus system and to compare the antibiotic susceptibility test results Kirby-Bauer disk diffusion method with MicroScan WalkAway 96 Plus automated identification and antimicrobial susceptibility testing system.  The study sample comprised 100 clinical isolates of species. They were all identified using MALDI-TOF MS and compared with other two identification systems.  Comparison of categorical variables by Fisher's exact test or Pearson's chi-square test was done. All statistical tools were two tailed, and a significant level  < 0.05 was used. All statistical tests were performed using SPSS v22.0 (Armonk IBM Corp., New York, United States). Cohen's kappa coefficients were also calculated and used as applicable.  MALDI-TOF MS revealed 92 , 2 , 3 , and 1 each was identified as , , and . There was moderate agreement between identification by MicroScan WalkAway and MALDI-TOF, and substantial agreement between conventional biochemical tests and MALDI-TOF. We found that there was a 100% categorical agreement with respect to susceptibility of aminoglycosides (amikacin, gentamicin, tobramycin) and cephalosporins (ceftazidime, cefepime, cefotaxime) between disk diffusion method and MicroScan WalkAway 96 Plus system. Total of 16 errors were observed.  Although MALDI-TOF MS could be useful to identify but not other species in the genus, it is a rapid, reliable method and can be routinely used in clinical laboratories.