Bacillus cereus G9241 Makes Anthrax Toxin and Capsule like Highly Virulent B. anthracis Ames but Behaves like Attenuated Toxigenic Nonencapsulated B. anthracis Sterne in Rabbits and Mice

Abstract

Bacillus cereus G9241 was isolated from a welder with a pulmonary anthrax-like illness. The organism contains two megaplasmids, pBCXO1 and pBC218. These plasmids are analogous to the Bacillus anthracis Ames plasmids pXO1 and pXO2 that encode anthrax toxins and capsule, respectively. Here we evaluated the virulence of B. cereus G9241 as well as the contributions of pBCXO1 and pBC218 to virulence. B. cereus G9241 was avirulent in New Zealand rabbits after subcutaneous inoculation and attenuated 100-fold compared to the published 50% lethal dose (LD 50 ) values for B. anthracis Ames after aerosol inoculation. A/J and C57BL/6J mice were comparably susceptible to B. cereus G9241 by both subcutaneous and intranasal routes of infection. However, the LD 50 s for B. cereus G9241 in both mouse strains were markedly higher than those reported for B. anthracis Ames and more like those of the toxigenic but nonencapsulated B. anthracis Sterne. Furthermore, B. cereus G9241 spores could germinate and disseminate after intranasal inoculation into A/J mice, as indicated by the presence of vegetative cells in the spleen and blood of animals 48 h after infection. Lastly, B. cereus G9241 derivatives cured of one or both megaplasmids were highly attenuated in A/J mice. We conclude that the presence of the toxin-and capsule-encoding plasmids pBCXO1 and pBC218 in B. cereus G9241 alone is insufficient to render the strain as virulent as B. anthracis Ames. However, like B. anthracis, full virulence of B. cereus G9241 for mice requires the presence of both plasmids.

Immunization of Mice with Formalin-Inactivated Spores from Avirulent Bacillus cereus Strains Provides Significant Protection from Challenge with Bacillus anthracis Ames

“…We previously reported that live spores of dcG9241, a plasmidcured derivative of B. cereus G9241, is avirulent in mice (18). In a preliminary study, we found that vaccination with live dcG9241 spores completely protected A/J mice against i.n.…”

“…B. cereus G9241, which was isolated from a welder with pulmonary anthrax-like disease, contains the pXO1 homolog pBCXO1 and an unrelated megaplasmid, pBC210 (8). B. cereus G9241 produces PA, LF, and EF from the pBCXO1-carried genes pag, lef, and cya, respectively (8,18). In addition, pBCXO1 encodes an intact and functional operon required for hyaluronic acid capsule synthesis (19), and pBC210 contains an operon that is necessary for production of a putative tetrasaccharide capsule (8,18,19).…”

Vaccine Protection against Bacillus cereus-Mediated Respiratory Anthrax-Like Disease in Mice

“…Unlike B. anthracis, these B. cereus strains are not designated select agents, and their virulence and pathogenic strategies have only recently been investigated. Wilson and coworkers studied the virulence of B. cereus G9241 spores in a rabbit model of inhalational anthrax-like disease (44). In contrast to B. anthracis strain Ames, which causes lethal respiratory disease in rabbits at a dose of Ն1 ϫ 10 5 spores, only one out of seven rabbits infected with B. cereus G9241 spores succumbed to aerosol challenge; the moribund rabbit had received a dose of approximately 10 7 spores (44).…”

“…Wilson and coworkers studied the virulence of B. cereus G9241 spores in a rabbit model of inhalational anthrax-like disease (44). In contrast to B. anthracis strain Ames, which causes lethal respiratory disease in rabbits at a dose of Ն1 ϫ 10 5 spores, only one out of seven rabbits infected with B. cereus G9241 spores succumbed to aerosol challenge; the moribund rabbit had received a dose of approximately 10 7 spores (44). By using intranasal spore challenge of anesthetized C57BL/6 mice, those authors calculated an LD 50 of 6.3 ϫ 10 5 B. cereus G9241 spores.…”

Bacillus cereus G9241 S-Layer Assembly Contributes to the Pathogenesis of Anthrax-Like Disease in Mice

“…When tested in mice with a peritoneal challenge model, B. cereus G9241 causes anthrax-like disease in a manner requiring genes for protective antigen (pagA, located on pBCXO1), BPS (bpsX-H on pBC218), and HA polysaccharides (hasACB on pBCXO1). Further, B. cereus G9241 causes respiratory anthrax-like disease in rabbits (41). Of note, B. cereus G9241 does not harbor the capBC-DAE genes, which are present on B. anthracis pXO2 (24,42).…”