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New Anthrax-Causing Clade Uncovered by Sequencing

NEW YORK (GenomeWeb) – An international team led by investigators in Germany has identified a new form of Bacillus cereus bacteria capable of causing anthrax.

The researchers sequenced the genomes of four Bacillus cereus representatives isolated from wild chimpanzees, gorillas, an elephant, and goats in several West and Central African countries. Their results, published online today in PLOS Neglected Tropical Diseases, pointed to the presence of strains classified as B. cereus biovar anthracis — a form of bacteria with similarities to both B. cereus and the traditional anthrax-causing bug B. anthracis.

"Our findings show the existence of a discrete clade of the B. cereus group capable of causing anthrax-like disease, found in areas of high biodiversity, which are possibly also the origin of the worldwide distributed B. anthracis," corresponding author Fabian Leendertz, a pathogenic microorganism epidemiology researcher at the Robert Koch-Institute, and his co-authors wrote.

He and his colleagues noted that "it will be important to adapt diagnostic methods for the detection of such atypical B. cereus strains — through the inclusion of molecular tools for the detection of the B. anthracis plasmids that appear to be the prerequisite to cause disease."

While traditional anthrax cases are usually pinned on B. anthracis bacteria, which contain the pXO1 and pXO2 virulence plasmids and are marked by low genetic diversity, there have been hints that other B. cereus bacteria carrying similar plasmids can cause the disease in humans and animals, the team explained.

To search for new disease culprits, the researchers did real-time PCR-based screening for the virulent pXO1 and pXO2 in tissue, bone, nose swab, and blood samples from livestock and wild animals in the Central African Republic's Dzanga-Ndoki National Park, a forested region in the Democratic Republic of Congo, Cameroon, and Côte d'Ivoire.

In the process, they found and cultivated B. cereus biovar anthracis in elephant, chimpanzee, gorilla, goat, and forest elephant samples, generally from animals that were sick or dead.

The team did whole-genome sequencing on new isolates from a gorilla in the Democratic Republic of Congo and an elephant from Central African Republic — alongside similar strains previously isolated from Cameroon and Côte d'Ivoire — using an Illumina MiSeq instrument.

When they compared the four new genomes to sequences from B. anthracis, B. cereus, and B. thuringiensis, the researchers uncovered genome SNPs and variants in pXO1 and pXO2 that made it possible to explore relationships between the clades.

In particular, that phylogenetic analysis suggested B. cereus biovar anthracis strains did belong to a distinct clade that seemed to be more closely tied to B. cereus than in B. anthracis, though it did contain the pXO1 and pXO2 virulence plasmids.

The researchers noted that the new clade appears to be present over large swathes of warm, tropical regions in West and Central Africa, though more detailed studies of B. cereus biovar anthracis and its distribution are needed.

"Establishing the impact of these pathogenic bacteria on threatened wildlife species will require systematic investigation," the team wrote. "Furthermore, the consumption of wildlife found dead by the local population and presence in a domestic animal reveal potential sources of exposure to humans."