Examination of the Culturable Microbiota from Low-Moisture Foods Imported into Canada for Antibacterial Activity against Listeria monocytogenes

Abstract

Listeria monocytogenes, a resilient and ubiquitous foodborne pathogen, is associated with a high case-fatality rate in humans. This study investigated the culturable microbiota of low-moisture foods (LMFs) imported into Canada to see how well bacteria isolated from these foods could inhibit or inactivate the growth of L. monocytogenes. Imported LMFs were acquired from various supermarkets in the Greater Toronto Area (Ontario, Canada). The foods included dried apples, bee pollen, cumin seeds, date fruits, fennel seeds, pistachios, raisins, and seaweed. Bacterial strains were isolated from the foods using blood agar and then screened using an in-house-designed growth inhibition plate assay against L. monocytogenes. The inhibitory strains detected were then identified using 16S rRNA sequencing. Diverse bacteria were recovered from the foods; 236 isolates belonging to 122 observed phenotypes were obtained. From the inhibition plate assays, 10 of the 11 imported LMFs harbored inhibitory strains against L. monocytogenes, whereby 48 of the collected isolates (20%) were found to produce a zone of inhibition against this pathogen. The inhibitory strains belonged to six genera (Acinetobacter, Aerococcus, Bacillus, Lysinibacillus, Paenibacillus, and Sporosarcina) and 15 unique species. Among all foods tested, the date fruit microbiota displayed the greatest number and diversity of anti–L. monocytogenes inhibitory strains. Overall, it was found that the culturable microbiota of LMFs, imported into Canada, possess bacterial members that can inhibit the growth of L. monocytogenes. These results could lead to the discovery of either novel antimicrobial metabolites or beneficial anti–L. monocytogenes bacteria that could be added to foods to inactivate and/or control L. monocytogenes.