Abstract
BackgroundThe complete genome sequences of 44 Bacillus cereus group isolates collected from diverse sources in Japan were analyzed to determine their genetic backgrounds and diversity levels in Japan. Multilocus sequence typing (MLST) and core-genome single-nucleotide polymorphism (SNP) typing data from whole-genome sequences were analyzed to determine genetic diversity levels. Virulence-associated gene profiles were also used to evaluate the genetic backgrounds and relationships among the isolates.ResultsThe 44 B. cereus group isolates, including soil- and animal-derived isolates and isolates recovered from hospitalized patients and food poisoning cases, were genotyped by MLST and core-genome SNP typing. Genetic variation among the isolates was identified by the MLST and core-genome SNP phylogeny comparison against reference strains from countries outside of Japan. Exploratory principal component analysis and nonmetric multidimensional scaling (NMDS) analyses were used to assess the genetic similarities among the isolates using gene presence and absence information and isolate origins as the metadata. A significant correlation was seen between the principal components and the presence of genes encoding hemolysin BL and emetic genetic determinants in B. cereus, and the capsule proteins in B. anthracis. NMDS showed that the cluster of soil isolates overlapped with the cluster comprising animal-derived and clinical isolates.ConclusionsMolecular and epidemiological analyses of B. cereus group isolates in Japan suggest that the soil- and animal-derived bacteria from our study are not a significant risk to human health. However, because several of the clinical isolates share close genetic relationships with the environmental isolates, both molecular and epidemiological surveillance studies could be used effectively to estimate virulence in these important pathogens.
Highlights
The complete genome sequences of 44 Bacillus cereus group isolates collected from diverse sources in Japan were analyzed to determine their genetic backgrounds and diversity levels in Japan
B. cereus is characterized by high-level pathogenicity and lifestyle diversity, a detailed analysis of virulence-associated genes carried by B. cereus group bacteria isolated from soil, animal feces, and human patients with food poisoning or nosocomial infections across Japan has not been performed
The resulting parasporal insecticide-producing isolates were classified as B. thuringiensis and the inclusion-negative isolates were designated as B. cereus
Summary
The complete genome sequences of 44 Bacillus cereus group isolates collected from diverse sources in Japan were analyzed to determine their genetic backgrounds and diversity levels in Japan. Outbreaks of disease caused by pathogenic Bacillus cereus strains showing virulence characteristics similar to those of B. anthracis have been restricted to a Okutani et al BMC Microbiology (2019) 19:296 strains, which pose a threat to human health, are present in Japanese soils. Multilocus sequence typing (MLST) and virulence gene profiling analyses of the emetic toxin-producing B. cereus strains associated with food poisoning or nosocomial infection have been conducted in many countries [7]. B. cereus is characterized by high-level pathogenicity and lifestyle diversity, a detailed analysis of virulence-associated genes carried by B. cereus group bacteria isolated from soil, animal feces, and human patients with food poisoning or nosocomial infections across Japan has not been performed. A comprehensive study of the genetic diversity among environmental and clinical B. cereus group isolates in Japan is warranted
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