Bacillus cereus Biovar Anthracis Causing Anthrax in Sub-Saharan Africa-Chromosomal Monophyly and Broad Geographic Distribution

Abstract

Through full genome analyses of four atypical Bacillus cereus isolates, designated B. cereus biovar anthracis, we describe a distinct clade within the B. cereus group that presents with anthrax-like disease, carrying virulence plasmids similar to those of classic Bacillus anthracis. We have isolated members of this clade from different mammals (wild chimpanzees, gorillas, an elephant and goats) in West and Central Africa (Côte d'Ivoire, Cameroon, Central African Republic and Democratic Republic of Congo). The isolates shared several phenotypic features of both B. anthracis and B. cereus, but differed amongst each other in motility and their resistance or sensitivity to penicillin. They all possessed the same mutation in the regulator gene plcR, different from the one found in B. anthracis, and in addition, carry genes which enable them to produce a second capsule composed of hyaluronic acid. 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. Establishing the impact of these pathogenic bacteria on threatened wildlife species will require systematic investigation. Furthermore, the consumption of wildlife found dead by the local population and presence in a domestic animal reveal potential sources of exposure to humans.

Fig 1. Geographic locations of carcasses.

Red diamonds show sites where Bacillus cereus bv anthracis isolates have been detected, the star represents the site where the bovine isolate B. cereus JF3964 was found. Locations (GPS data) and animal carcasses for B. cereus bv anthracis are: Taï National Park (CI)–chimpanzee (5°50.876’N, 7°19.679’W); Dja Wildlife Reserve (CAM)–gorilla, chimpanzee (3°07.589’N, 13°06.543’E); Dzanga-Sangha (RCA)–gorilla, chimpanzee, elephant (2°53.747’N, 16°24.208’E); Luebo (DRC)–goat (5°21.074’S, 21°25.298’E). Strain JF3964: Koza (CAM)–cattle (10°57.769’N, 13°55.560’E).

Fig 2. Maximum likelihood tree based on core chromosomal SNP data.

A: Full tree. B: Zoom-in focused on the Bacillus cereus biovar anthracis clade. Bacillus anthracis sequences are black, Bacillus cereus and Bacillus thuringiensis red and B. cereus bv anthracis blue. Branch support values were estimated by approximate likelihood ratio tests and are only reported for these internal branches not supported by maximal values. This tree was rooted with TempEst v1.5.

Fig 3. Maximum likelihood tree based on core plasmid SNP data.

A: pXO1. B: pXO2. Bacillus anthracis sequences are black, Bacillus cereus red and Bacillus cereus biovar anthracis blue. Branch support values were estimated by approximate likelihood ratio tests and are only reported for these internal branches not supported by maximal values. The trees were rooted with TempEst v1.5.