Epidemiologic Investigation of Two Welder's Anthrax Cases Caused by Bacillus Cereus Group Bacteria: Occupational Link Established by Environmental Detection

Characterization of the Bacillus cereus Group Isolated from Ready-to-Eat Foods in Poland by Whole-Genome Sequencing

Bacillus cereus sensu lato can contaminate food and cause food poisoning by producing toxins such as cereulide, toxin BL, and cytotoxin K. In this study, we retrospectively analyzed B. cereus sensu lato from retail food products and food poisoning cases using PCR methods to determine their virulence profiles. A new toxin profile, encoding all four toxins (hbl, nhe, cytK, ces), was found in 0.4% of isolates. The toxin profiles, classified into A-J, revealed that 91.8% harbored nhe genes, while hbl, cytK, and ces were detected in 43.8%, 46.9%, and 4.2% of isolates, respectively. Whole-genome sequencing (WGS) identified four distinct species within the B. cereus group, with 21 isolates closely related to B. cereus sensu stricte, 25 to B. mosaicus, 2 to B. toyonensis, and 1 to B. mycoides. Three novel sequence types (STs 3297, 3298, 3299) were discovered. Antibiotic resistance genes were common, with 100% of isolates carrying beta-lactam resistance genes. Fosfomycin (80%), vancomycin (8%), streptothricin (6%), tetracycline (4%), and macrolide resistance (2%) genes were also detected. These results highlight the genetic diversity and antibiotic resistance potential of B. cereus sensu lato strains in Polish food products.

Investigating Anthrax-Associated Virulence Genes among Archival and Contemporary Bacillus cereus Group Genomes

Bacillus anthracis causes anthrax through virulence factors encoded on two plasmids. However, non-B. anthracis organisms within the closely related, environmentally ubiquitous Bacillus cereus group (BCG) may cause an anthrax-like disease in humans through the partial adoption of anthrax-associated virulence genes, challenging the definition of anthrax disease. To elucidate these phenomena and their evolutionary past, we performed whole-genome sequencing on non-anthracis BCG isolates, including 93 archival (1967-2003) and 5 contemporary isolates (2019-2023). We produced annotated genomic assemblies and performed a pan-genome analysis to identify evidence of virulence gene homology and virulence gene acquisition by linear inheritance or horizontal gene transfer. At least one anthrax-associated virulence gene was annotated in ten isolates. Most homologous sequences in archival isolates showed evidence of pseudogenization and subsequent gene loss. The presence or absence of accessory genes, including anthrax-associated virulence genes, aligned with the phylogenetic structure of the BCG core genome. These findings support the hypothesis that anthrax-associated virulence genes were inherited from a common ancestor in the BCG and were retained or lost across different lineages, and contribute to a growing body of work informing public health strategies related to anthrax surveillance and identification.

Whole genome sequencing of Bacillus anthracis isolated from animal in the 1960s, Brazil, belonging to the South America subclade

Bacillus anthracis causes anthrax disease and can affect humans and other animals. This zoonotic disease has an impact on the economic and health aspects. B. anthracis population is divided into three major clades: A (with worldwide distribution), B, and C (restricted to specific regions). Anthrax is most common in agricultural regions of central and southwestern Asia, sub-Saharan Africa, Southern and Eastern Europe, the Caribbean, and Central and South America. Here, we sequenced by short and long reads technologies to generate a hybrid assembly of a lineage of B. anthracis recovered from animal source in the 1960s in Brazil. Isolate identification was confirmed by phenotypic/biochemical tests and MALDI-TOF MS. Antimicrobial susceptibility was performed by in-house broth microdilution. B. anthracis IAL52 was susceptible to penicillin, amoxicillin, doxycycline, levofloxacin, and tetracycline but non-susceptible to ciprofloxacin. IAL52 was classified as sequence type ST2, clade A.Br.069 (V770 group). Sequencing lineages of B. anthracis, especially from underrepresented regions, can help determine the evolution of this critical zoonotic and virulent pathogen.

Pathogenic Bacilli as an Emerging Biothreat?

Bacillus anthracis, present as a very durable endospore in soil, causes zoonotic illness which is mainly associated with herbivores and domestic animals. Human cases are scarce and often involve populations close to infected livestock. If anthrax is no longer of public health concern in developed countries, B. anthracis is one of the top-tier biological weapon agents. It is classified by the CDC as a category A agent. Since 1994, emerging strains of Bacillus cereus have been associated with anthrax-like disease in mammals. Some clinical strains of B. cereus harbor anthrax-like plasmid genes (pXO1 and pXO2) associated with non-human primate and human infections, with the same clinical presentation of inhalation anthrax and mortality rates. Although currently restricted to certain limited areas of circulation, the emergence of these new strains of B. cereus extends the list of potential agents possibly usable for bioterrorism or as a biological weapon. It is therefore important to improve our knowledge of the phylogeny within the B. cereus sensu lato group to better understand the origin of these strains. We can then more efficiently monitor the emergence of new strains to better control the risk of infection and limit potentially malicious uses.