Application of VITEK® MS System for the Identification of Pathogens from the Isolated Colonies on Chromogenic Media from a Variety of Food Samples

Introduction: The VITEK^®MS system uses Matrix Assisted Laser Desorption Time-of-Flight Mass Spectrometry (MALDI-TOF MS) to analyze spectral patterns of ionized molecules derived from intact microorganisms for their identification. This novel system provides microbial identification with similar specificity as 16S rRNA gene sequencing and could prove valuable for identification of pathogens from foods.

Purpose: Evaluate a MALDI-TOF MS based system for the identification of Salmonella, Listeria and Campylobacter spp. from isolated colonies on chromogenic media from a variety of food products.

Methods: Thirty strains each of Salmonella spp., and Listeria spp. and 15 strains of Campylobacter spp. were artificially inoculated into a variety of food matrices independently, enriched, and detected using target specific systems and isolated on selective chromogenic media and differential media including ALOA^® and PALCAM for Listeria spp.; CampyFood Agar for Campylobacter spp.; and ASAP™ and XLD for Salmonella spp. Typical colonies (2-5) on each media were identified using the MALDI-TOF MS based system.

Results: All Salmonella, Listeria and Campylobacter strains were recovered from enriched food samples on the chromogenic media and differential media studied and correctly identified (100%) using the MALDI-TOF MS based system. Additionally, colonies of all strains on the chromogenic media and sheep blood agar from pure cultures were also correctly (100%) identified.

Significance: Identification of the pathogen after their detection from food samples could be directly performed by VITEK MS using the colonies isolated on selective chromogenic media. This has potential to eliminate the requirement of isolating colonies on non-selective media before their further identification.