The Role of Matrix-Assisted Laser Desorption Ionization-Time of Flight- Mass Spectrometry (MALDI-TOF-MS) in the Identification of Non-fermenting Gram-Negative Bacilli from Clinical Isolates in a Tertiary Care Hospital

Abstract

Non-fermenting Gram-negative bacilli (NFGNB) are a heterogeneous group of aerobic non-spore forming bacilli. Matrix-Assisted Laser Desorption Ionization-Time of Flight- Mass Spectrometry (MALDI-TOF-MS) is a quick, precise diagnostic method that could identify the isolates at the species level. The aim of the study is to identify the non-fermenters isolated from various clinical infections by MALDI-TOF analysis and to detect the antibiogram of these isolates. The non-fermenters were isolated from various clinical specimens, plated on Blood agar and MacConkey agar and incubated at 37⁰C for 24 hours. Identification was done on the basis of colony morphology, Gram stain, and MALDI-TOF Analysis. Antimicrobial Susceptibility Testing was done by Kirby- Bauer Disc Diffusion Technique using commercially available antibiotics on Muller-Hinton Agar. A total of 360 samples were studied. The majority of the non-fermenters were from Blood/ Body fluids (39.72%). Acinetobacter spp (31.67%) was the most common isolate, followed by Pseudomonas spp (22.50%). Other non-fermenters like Stenotrophomonas maltophilia, Burkholderia spp, Elizabethkingia spp, Achromobacter spp, Chryseobacterium spp, Ralstonia spp, Pandoraea spp, Rhizobium radiobacter, Sphingomonas spp, Ochrobactrum spp, Myroides odoratimimus and Brevundimonas spp were rarely isolated non-fermenters. Most of the strains were multi drug resistant to commonly used antibiotics like Cephalosporins, Aminoglycosides and Carbapenems. Our results showed that identifying non-fermenters using MALDI-TOF MS is a reliable and rapid technique that shortens the time to initiate appropriate therapy and even the length of the hospital stay.