Diversity and Fitness of Listeria spp. Isolated from Two Watersheds in Nova Scotia, Canada

Introduction:  There have been many studies on the ecology and fitness (i.e., the ability of an organism to survive and reproduce under various environmental conditions) of L. monocytogenes in an effort to better understand the transmission pathways and the factors that help L. monocytogenes persist in food processing facilities. However, there are limited studies comparing the fitness of other Listeria strains, and most are limited to a few species such as L. welshimeri, L. innocua, and L. ivanovii.

Purpose:  The purpose of this study was to provide a better understanding of natural reservoirs of pathogenic and other Listeria species, as well as the factors which may contribute to their survival in food processing environments.

Methods:  Colony PCR and Sanger sequencing targeting the 16S ribosomal RNA and sigB genes were used to identify 679 naturally occurring Listeria strains isolated from fresh water samples obtained from one urban and one rural watershed in Nova Scotia, Canada. For each of the detected Listeriaspecies, the fitness of two isolates from each watershed was further evaluated through assays testing motility, biofilm formation (100% RH, 15°C), desiccation tolerance (23% RH, 15°C) and resistance of planktonic and sessile cells to benzalkonium chloride (BAC).

Results:  L. monocytogenes (26% of the 679 strains), L. innocua (52%) and L. seeligeri (18%) were isolated from both watersheds. L. welshimeri (3%) and L. fleischmannii (1%) were only isolated from the rural watershed. L. fleischmannii and L. innocua formed significantly (P < 0.05) less biofilm than the other species. L. monocytogenes strains from the urban and rural watersheds were the most and least desiccation-resistant, respectively. Generally, the non-motile L. fleischmannii was the most susceptible to BAC.

Significance: This research provides insights into natural reservoirs of pathogenic and non-pathogenic Listeria, and the fitness that may help Listeria spp. persist in food processing plants.