Genomic surveillance of Bacillus cereus sensu lato strains isolated from meat and poultry products in South Africa enables inter- and intra-national surveillance and source tracking
Abstract
Members of the Bacillus cereus sensu lato (s.l.) species complex, also known as the B. cereus group, vary in their ability to cause illness, but are frequently isolated from foods, including meat products; however, food safety surveillance efforts that employ whole-genome sequencing (WGS) often neglect these potential pathogens. Here, WGS was used to characterize B. cereus s.l. strains (n = 25) isolated during surveillance of meat products in South Africa. Strains were collected from beef, poultry, and mixed meat products obtained from (i) retail outlets, processing plants, and butcheries across six South African provinces (n = 15, 7, and 1, respectively), and (ii) imports in cold stores (n = 2). Strains were assigned to panC Groups IV, III, II, and V (n = 18, 5, 1, and 1, respectively) and spanned multiple genomospecies, regardless of the taxonomy used. All strains possessed diarrheal toxin-encoding genes, while one sequence type 26 (ST26) strain possessed cereulide (emetic toxin) synthetase-encoding genes. No strains harbored anthrax toxin- or capsule-encoding genes. The 25 strains were partitioned into 15 lineages via in silico seven-gene multi-locus sequence typing (MLST), six of which contained multiple strains sequenced in this study, which were identical or nearly identical at the whole-genome scale. Five MLST lineages contained (nearly) identical genomes collected from two or three South African provinces; one MLST lineage contained nearly identical genomes from two countries (South Africa and the Netherlands), indicating that B. cereus s.l. can spread intra- and inter-nationally via foodstuffs.
Importance
Nation-wide foodborne pathogen surveillance programs that employ high-resolution genomic methods have been shown to provide vast public health and economic benefits. However, B. cereus s.l. are often overlooked during large-scale, routine WGS efforts. Thus, to our knowledge, no studies to date have evaluated the potential utility of WGS for B. cereus s.l. surveillance and source tracking in foodstuffs. In this proof-of-concept study, we applied WGS to B. cereus s.l. strains collected via South Africa’s national surveillance program of domestic and imported meat products, and we provide strong evidence that B. cereus s.l. can be disseminated intra- and inter-nationally via the agro-food supply chain. Our results showcase that WGS can be used for source tracking of B. cereus s.l. in foods, although future WGS and isolate metadata collection efforts are needed to ensure that B. cereus s.l. surveillance initiatives are on par with those of other foodborne pathogens.
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