Jc. Sirard et al., Characterization of a plasmid region involved in Bacillus anthracis toxin production and pathogenesis, INT J MED M, 290(4-5), 2000, pp. 313-316
The germination of spores within the host is the initial step of anthrax in
fection. We have shown, using immunofluorescence staining, confocal scannin
g laser microscopy and image cytometry analysis, that the alveolar macropha
ge is the primary site of B. anthracis germination in a murine inhalation i
nfection model. B. anthracis germinated inside macrophages, in vesicles der
ived from the phagosomal compartment. We have demonstrated that the toxin g
enes and their trans-activator, AtxA, are expressed within the macrophages
after germination. It was also shown that the pXO1 plasmid strongly enhance
d capsule formation and that this influence is mediated by AtxA. This indic
ates the existence of a regulon where AtxA is the regulatory protein acting
on genes located on different plasmids. We identified a tricistronic germi
nation operon gerX located between the pag and atxA genes on the 40-kb toxi
n-encoding fragment of pXO1. Analysis of a gerX null mutant indicated that
gerX-encoded proteins are involved in the virulence of B. anthracis.