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

Abstract

bBacillus anthracis spores are the infectious form of the organism for humans and animals. However, the approved human vaccine in the United States is derived from a vegetative culture filtrate of a toxigenic, nonencapsulated B. anthracis strain that primarily contains protective antigen (PA). Immunization of mice with purified spore proteins and formalin-inactivated spores (FIS) from a nonencapsulated, nontoxigenic B. anthracis strain confers protection against B. anthracis challenge when PA is also administered. To investigate the capacity of the spore particle to act as a vaccine without PA, we immunized mice subcutaneously with FIS from nontoxigenic, nonencapsulated B. cereus strain G9241 pBCXO1 ؊ /pBC210 ؊ (dcG9241), dcG9241 ⌬bclA, or 569-UM20 or with exosporium isolated from dcG9241. FIS vaccination provided significant protection of mice from intraperitoneal or intranasal challenge with spores of the virulent B. anthracis Ames or Ames ⌬bclA strain. Immunization with dcG9241 ⌬bclA FIS, which are devoid of the immunodominant spore protein BclA, provided greater protection from challenge with either Ames strain than did immunization with FIS from BclA-producing strains. In addition, we used prechallenge immune antisera to probe a panel of recombinant B. anthracis Sterne spore proteins to identify novel immunogenic vaccine candidates. The antisera were variably reactive with BclA and with 10 other proteins, four of which were previously tested as vaccine candidates. Overall our data show that immunization with FIS from nontoxigenic, nonencapsulated B. cereus strains provides moderate to high levels of protection of mice from B. anthracis Ames challenge and that neither PA nor BclA is required for this protection.

Acetalated Dextran Microparticulate Vaccine Formulated via Coaxial Electrospray Preserves Toxin Neutralization and Enhances Murine Survival Following Inhalational Bacillus Anthracis Exposure

“…Given this difficulty, there is a paucity of studies where mice have been challenged this way. When considering the limited inhalational Ames challenges that have been performed, the protection achieved in our study was very similar to the protection provided by formaldehyde‐inactivated spores and a two‐fold higher rPA dose (20 μg) delivered via a transcutaneous route . We also demonstrated improved protection compared to a study using a combinatorial immunogen consisting of rPA and spore antigens .…”

The roles of AtxA orthologs in virulence of anthrax‐like Bacillus cereus G9241

“…A list of strains and plasmids used for mutagenesis and primers used can be found in Supporting Information Tables S1 and S2, respectively. Briefly, to generate the vectors for insertional mutagenesis, an Ω‐kanamycin or Ω‐spectinomycin cassette was cloned between ∼1 kb PCR products that flank the 5′ and 3′ ends of the genes of interest in pGEM‐T, subcloned into pUTE583, and introduced into G9241 as described previously (Vergis et al ., ). For markerless deletion, the ∼1 kb PCR products that flank the 5′ and 3′ ends of the gene of interest were cloned into pGEM‐T, subcloned into pJMS1, and introduced into G9241 as described in the Supporting Information.…”

The Exosporium Layer of Bacterial Spores: a Connection to the Environment and the Infected Host

“…Animal studies of the efficacy of the human vaccine found that protection against the most virulent strains of B. anthracis required the addition of spore antigens to the vaccination regimen (144)(145)(146)(147). Improved vaccine protection was observed when the added spore antigens included inactivated whole spores (147)(148)(149)(150), live attenuated spores (146,(151)(152)(153)(154), BclA (81,83,148,155), BxpB (68,148), and BAS5303 (68,148). Antibodies directed against whole spores or, specifically, BclA have been shown to be inhibitory to spore germination in vitro (148,156).…”