Purpose: The aim of this study was to evaluate performance of the new methods, specifically for inclusivity, exclusivity and for the detection of Listeria monocytogenes and Listeria spp. in environmental samples.
Methods: Pure cultures of known identity, both inclusive and exclusive strains from diverse sources were tested using the new molecular methods after growth in demi-Fraser broth or non-selective broth. Paired food-plant environmental sponge samples were collected using a sampling device wetted with Dey-Engley Neutralizing Broth then tested using the traditional FDA-BAM method and the new molecular methods. Presumptive results from the new methods were confirmed using microscopic, biochemical and molecular characterization according to the FDA-BAM method, followed by 16S sequencing.
Results: Of the forty-four pure cultures, all were correctly identified using the new methods. Among the ninety environmental sample locations analyzed, three positive samples were identified by both the new molecular method and the FDA-BAM method. Using 16S sequencing, two of these isolates were identified as either Listeria riparia or Listeria booriae, two newly recognized Listeria species that cannot be differentiated based on the partial 16S rDNA sequence amplified.
Significance: This study demonstrates that recently reported and newly recognized Listeria species can be found in food processing environments with advanced detection and characterization methods. In addition, this study shows that the new detection method is reliable, accurate and offers advantages to the end user, including a faster time-to-result compared to the cultural method.