Inhalation anthrax is a rare disease that is almost invariably fatal. This study determined whether a prolonged course of postexposure antibiotics with or without vaccination would protect monkeys exposed to a lethal aerosol dose of Bacillus anthracis when the antibiotic was discontinued. Beginning 1 day after exposure, groups of 10 animals were given penicillin, ciprofloxacin, doxycycline, doxycycline plus vaccination, vaccination alone, or saline. Antibiotics were administered for 30 days and then discontinued. Vaccine was given on days 1 and 15. Two animals died of causes other than anthrax and were not included in the statistical analysis. Nine of 10 controls and 8 of 10 animals given only vaccine died. Each antibiotic regimen completely protected animals while on therapy and provided significant long-term protection upon discontinuance of the drug (penicillin, 7 of 10 survived, P < .02; ciprofloxacin, 8 of 9 survived, P < .002; doxycycline, 9 of 10 survived, P < .002; doxycycline plus vaccination, 9 of 9 survived, P < .0002). Protection against rechallenge was provided by combining postexposure antibiotic treatment with vaccination.

No abstract

Bacillus spp. and Clostridium spp. form a specialized cell type, called a spore, during a multistep differentiation process that is initiated in response to starvation. Spores are protected by a morphologically complex protein coat. The Bacillus anthracis coat is of particular interest because the spore is the infective particle of anthrax. We determined the roles of several B. anthracis orthologues of Bacillus subtilis coat protein genes in spore assembly and virulence. One of these, cotE, has a striking function in B. anthracis: it guides the assembly of the exosporium, an outer structure encasing B. anthracis but not B. subtilis spores. However, CotE has only a modest role in coat protein assembly, in contrast to the B. subtilis orthologue. cotE mutant spores are fully virulent in animal models, indicating that the exosporium is dispensable for infection, at least in the context of a cotE mutation. This has implications for both the pathophysiology of the disease and next-generation therapeutics. CotH, which directs the assembly of an important subset of coat proteins in B. subtilis, also directs coat protein deposition in B. anthracis. Additionally, however, in B. anthracis, CotH effects germination; in its absence, more spores germinate than in the wild type. We also found that SpoIVA has a critical role in directing the assembly of the coat and exosporium to an area around the forespore. This function is very similar to that of the B. subtilis orthologue, which directs the assembly of the coat to the forespore. These results show that while B. anthracis and B. subtilis rely on a core of conserved morphogenetic proteins to guide coat formation, these proteins may also be important for species-specific differences in coat morphology. We further hypothesize that variations in conserved morphogenetic coat proteins may play roles in taxonomic variation among species.

No abstract

The development of new approaches to combat anthrax requires that the pathogenesis and host response to Bacillus anthracis spores be better understood. We investigated the roles that macrophages and neutrophils play in the progression of infection by B. anthracis in a mouse model. Mice were treated with a macrophage depletion agent (liposome-encapsulated clodronate) or with a neutrophil depletion agent (cyclophosphamide or the rat anti-mouse granulocyte monoclonal antibody RB6-8C5), and the animals were then infected intraperitoneally or by aerosol challenge with fully virulent, ungerminated B. anthracis strain Ames spores. The macrophage-depleted mice were significantly more susceptible to the ensuing infection than the salinepretreated mice, whereas the differences observed between the neutropenic mice and the saline-pretreated controls were generally not significant. We also found that augmenting peritoneal neutrophil populations before spore challenge did not increase resistance of the mice to infection. In addition, the bacterial load in macrophage-depleted mice was significantly greater and appeared significantly sooner than that observed with the saline-pretreated mice. However, the bacterial load in the neutropenic mice was comparable to that of the saline-pretreated mice. These data suggest that, in our model, neutrophils play a relatively minor role in the early host response to spores, whereas macrophages play a more dominant role in early host defenses against infection by B. anthracis spores.Bacillus anthracis is the etiological agent of anthrax and a proven agent of bioterrorism (12,16,27,41). B. anthracis sporulates in the presence of environmental stresses, such as inadequate nutrient supply or desiccation (31). The spore, the infectious form of the organism, can remain dormant and viable for decades until favorable conditions are encountered. Upon infection, the spore germinates (42) and begins to outgrow into toxin-producing (2, 4), replicating bacilli, which can ultimately kill the infected host (26). Little information exists concerning the earliest stages of spore germination in vivo and the nature of the host response to the spores. It has been proposed that macrophages phagocytose spores, promote spore germination, and play a role that has been likened to a "Trojan horse" during an infection with B. anthracis spores (11,(21)(22)(23)(24)30). However, macrophages have also been shown to be sporicidal in vitro (3,47,59,60,64) and have a protective role for the host infected with B. anthracis spores (7).Neutrophils are widely considered the first responders to an infection and can be observed at sites of infection significantly sooner than migrating macrophages (38). The roles of neutrophils during an infection with B. anthracis also remain unclear. The few accounts available suggest that they may play a more minor role, secondary to that of macrophages, in host defenses against anthrax (20,50,64). Nevertheless, the relative role of these phagocytes in the host response and their possible inte...

No abstract

Pathogenesis of Bacillus anthracis is associated with the production of lethal toxin (LT), which activates the murine Nalp1b/Nlrp1b inflammasome and induces caspase-1–dependent pyroptotic death in macrophages and dendritic cells. In this study, we investigated the effect of allelic variation of Nlrp1b on the outcome of LT challenge and infection by B. anthracis spores. Nlrp1b allelic variation did not alter the kinetics or pathology of end-stage disease induced by purified LT, suggesting that, in contrast to previous reports, macrophage lysis does not contribute directly to LT-mediated pathology. However, animals expressing a LT-sensitive allele of Nlrp1b showed an early inflammatory response to LT and increased resistance to infection by B. anthracis. Data presented here support a model whereby LT-mediated activation of Nlrp1b and subsequent lysis of macrophages is not a mechanism used by B. anthracis to promote virulence, but rather a protective host-mediated innate immune response.

The efficacy and mechanisms of protection of two live vaccines and of a protective antigen (PA) vaccine against Bacillus anthracis were studied in inbred mice. Mice that differed in their natural resistance to killing by Sterne, a non-encapsulated, toxigenic vaccine strain of B. anthracis, were used . Vaccination with live Sterne spores protected Sterne-resistant mice against challenge with the virulent Vollum 1 B (V1 B) strain of B. anthracis, but only at doses of Sterne 0 .1 50% lethal dose . The live B . subtilis recombinant strain PA2, which produces the PA component of anthrax toxin, fully protected (CBA/J) or partially protected (BALB/cJ) Sterneresistant mice against V1 B . Neither immunization with the cell-free PA vaccine nor passive administration of anti-PA antiserum protected Sterne-resistant mice against V1 B . Sternesusceptible A/J mice were not protected against V1 B by either live vaccine or by the PA vaccine . However, immunization with strain PA2 induced anti-PA antibody and protected A/J mice against Sterne . A/J mice passively treated with antitoxin antibodies also survived Sterne, and survivors were then partially protected against V1 B . Thus, immunity to Sterne correlated with an effective anti-PA response . Immunity to fully virulent V1 B also required PA but may involve mechanisms in addition to humoral immunity .