Comparative Evaluation of Sampling Devices and Enrichment Broths for Environmental Testing of Listeria monocytogenes on Different Food Processing Surfaces

Introduction: Effective environmental testing procedures are critical for identifying source of contamination in food processing facilities; however, the current Food and Drug Administration Bacteriological Analytical Manual don’t have validated methods for environment testing of Listeria spp. 

Purpose: This research project was focused on the development and validation of testing procedures including sample collection and enrichment of Listeria spp. in food processing environments.

Methods: Five different surfaces, stainless steel, wood, rubber, glass and plastic were artificially inoculated with Listeria spp. and/or competing microflora. Four commercial brands of swabs and two commercial brands of sponges were comparatively evaluated for their ability to recover Listeria spp. from these surfaces. The enrichment scheme of half Fraser broth as pre-enrichment followed by Fraser broth as selective enrichment was compared to the enrichment scheme off our hours of enrichment in Buffered Listeria Enrichment Broth (BLEB) without antibiotics followed by 44 hours of enrichment in BLEB with antibiotics for their ability to enrich samples collected from these surfaces. 

Results: The data show that there was no statistical difference (P>0.05) in the ability to collect environmental samples among all brands of swabs and between two brands of sponges. The two enrichment schemes appear to be equivalent for enriching Listeria spp. from artificially contaminated surfaces (P>0.05).

Significance: The sources of several listeriosis outbreaks were traced back to processing environment. Development and evaluation of environmental testing procedures can contribute to preventive control and outbreak investigation of Listeria monocytogenes.