Sterne B.anthracis

Lars Andrup andrup at
Fri Apr 17 02:57:17 EST 1998

"I Garsan" <jigs1941963 at HOTMAIL.COM> skrev i artiklen
<19980415172517.12135.qmail at>...
> Hi,
> A lot of Pharmaceutical Labs are using the Sterne strain of Bacillus 
> anthracis for vaccine production because this strain has low virulence 
> by its uncapsulated phenotype. My questions are: Can the Sterne strain 
> change to capsulated phenotype (so more virulent) through in vivo or in 
> vitro pass?. Can shift the haemolysis production or colonial suface 
> characteristics be connected with virulence in this strain?.
> Kind regards
> I.Garsan

Dear Garsan
Virulent strains of Bacillus anthracis contain two large plasmids  encoding
the functions required for pathogenicity. One of the plasmids, pXO1 (200
kb), encodes the three components of the anthrax toxin and the other
plasmid, pXO2 (100 kb), encodes the glutamic-acid capsule of the bacterium.

The classic vaccine made by Pasteur was probably cured of plasmid pXO1 (he
made it from virulent strains by passing through animals, growth at
elevated temp. etc. – sometimes they didn't work). The avirulent Sterne
strain does not have the pXO2 plasmid, hence it produces toxins but no

There is a, maybe theoretical, risk that if these two strains were brought
together a virulent strain may be formed. Both plasmids have been shown to
be mobilizable via horizontal DNA-transfer (e.g. mediated by conjugative
plasmids, which are often present in related species of Bacillus). However,
without  exogenous DNA I can't imagine that the Sterne strain could revert
to a anthrax-causing bacterium.



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Lars Andrup, senior researcher
National Institute of Occupational Health
Lersø Parkallé 105, DK-2100 Copenhagen, Denmark
phone:+45 3916-5223 fax: +45 3916-5201
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