Abstract
Microorganisms that cause foodborne illnesses challenge the food industry; however, environmental studies of these microorganisms on raw grain, prior to food processing, are uncommon. Bacillus cereus sensu lato is a diverse group of bacteria that is common in our everyday environment and occupy a wide array of niches. While some of these bacteria are beneficial to agriculture due to their entomopathogenic properties, others can cause foodborne illness; therefore, characterization of these bacteria is important from both agricultural and food safety standpoints. We performed a survey of wheat and flax grain samples in 2018 (n = 508) and 2017 (n = 636) and discovered that B. cereus was present in the majority of grain samples, as 56.3% and 85.2%, in two years respectively. Whole genome sequencing and comparative genomics of 109 presumptive B. cereus isolates indicates that most of the isolates were closely related and formed two genetically distinct groups. Comparisons to the available genomes of reference strains suggested that the members of these two groups are not closely related to strains previously reported to cause foodborne illness. From the same data set, another, genetically more diverse group of B. cereus was inferred, which had varying levels of similarity to previously reported strains that caused disease. Genomic analysis and PCR amplification of genes linked to toxin production indicated that most of the isolates carry the genes nheA and hbID, while other toxin genes and gene clusters, such as ces, were infrequent. This report of B. cereus on grain from Canada is the first of its kind and demonstrates the value of surveillance of bacteria naturally associated with raw agricultural commodities such as cereal grain and oilseeds.
Highlights
Bacillus cereus sensu lato (B. cereus) is a group of Gram-positive, rod-shaped, spore forming bacteria, which occupy diverse lifestyles and ecological niches, which is facilitate by its diversity at the gene and genome level [1]
Wheat samples from Harvest Sample Program (HSP) belonged to two wheat classes that are defined according to the Canadian grain registration system, Canadian Western Red Spring (CWRS) and Canadian Eastern Red Spring (CERS) and originated from farms across Canada
In 2018, the highest incidence of B.cereus positive samples were detected in CWRS HSP and CERS HSP respectively
Summary
Bacillus cereus sensu lato (B. cereus) is a group of Gram-positive, rod-shaped, spore forming bacteria, which occupy diverse lifestyles and ecological niches, which is facilitate by its diversity at the gene and genome level [1]. These bacteria and their propagules are present in soil, dust, plants, water, feces, and animal guts [2,3,4]. The diversity and ubiquity of B. cereus makes strain monitoring challenging. As the human population continues to rise and our food production and processing intensify, it will be of utmost importance to understand the various sources of these bacteria, as well as their diversity
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