ANTHRAX, VIRULENCE
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A ProMED-mail post
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Date: Fri, 28 Mar 2003 17:43:32 -0500
From: ProMED-mail <promed@promedmail.org>
Source: NY Times Online [edited]
<http://www.nytimes.com/2003/03/27/international/worldspecial/27ANTH.html>


Scientists have discovered why different strains of the bacterium that 
causes anthrax differ so much in virulence, a finding that in theory could 
produce more effective vaccines and better tools for distinguishing and 
tracking the lethal germ. But the finding could also aid the creation of 
designer varieties of anthrax that are potentially deadlier to humans. 
Because of that potential danger, a debate occurred over whether the 
discovery should be kept secret, scientists said. In the end, it was 
decided that the benefits of publication outweighed the risks.

The discovery was made by 6 scientists at Louisiana State University, the 
Lawrence Livermore National Laboratory, and the United States Army Medical 
Research Institute of Infectious Diseases, the nation's top center for 
studying germ defenses. It is published in the current Journal of Clinical 
Microbiology. The lead author, Dr. Pamala R. Coker, formerly at L.S.U. and 
now at the Livermore laboratory in California, spearheaded the research for 
her Ph.D. dissertation. The Livermore laboratory once pioneered nuclear 
arms but increasingly studies biology and germ defenses.

The team's finding centers on the anthrax genome, which consists of a 
single large chromosome and 2 small circles of DNA, known as plasmids, that 
carry extra genes. The scientists found that, contrary to common belief, 
each anthrax bacterium carries not just one set of plasmids but up to 243 
copies of the first and up to 32 copies of the second, which is known as 
pX02. The more copies of this plasmid in a bacterial strain, the more 
capable it is of causing disease, the scientists said.

The [virulence] research was conducted in guinea pigs. The scientists 
found, for example, that an anthrax strain from Mozambique that possessed 
just one pX02 plasmid killed 25 percent of the test animals. But a strain 
from Australia with 32 copies of the plasmid left all the guinea pigs dead. 
[They] also reported that added factors like subtle features of the 
bacterium's DNA chromosome appeared to help determine virulence. Thus, the 
anthrax that killed 5 Americans in the germ attacks of 2001 -- the 
so-called Ames strain -- was found to possess just 2 copies of pX02. But it 
nonetheless killed 62 percent of the guinea pigs.

The pX02 plasmid carries genes that let the anthrax bacterium fashion an 
outer protein coat that acts as a defensive shield to thwart the immune 
system of hosts. The scientists suspect that multiple copies of pX02 
thicken that coating, letting the germ escape immune damage and multiply to 
do extensive harm.

Scientists had previously identified 89 types of anthrax as genetically 
distinct but had failed to discover what determined their wide differences 
in virulence. The plasmid findings, they said, opened a new window on that 
question. [While more research needs to be done to verify these 
observations, and if confirmed they may help in the development of new 
vaccines - Mod.MHJ] it could also aid investigations of germ attacks. Dr. 
Coker of the Livermore laboratory said the finding could help forensic 
scientists track down the country and laboratory from which the weapon 
arose. That, she said, was possible because the plasmid technique acted as 
a kind of microscope to reveal finer genetic distinctions among the 89 
known varieties of anthrax. [She] conceded that the research in theory 
could also help a genetic engineer make a more deadly form of anthrax by 
increasing the number of pX02 plasmids.

Dr. Kaplan of the University of Texas, who heads the publication board of 
the American Society for Microbiology in Washington, said no reviewer or 
official of the society raised objections to publication of the plasmid 
paper, even though the White House has urged scientists to screen their 
work carefully for possible harm to national security.

Steve Wampler, a spokesman at the California laboratory, said the plasmid 
research was done before Dr. Coker came to Livermore, but the laboratory 
nonetheless put the paper through a careful security review. "In the end," 
he said, "it was decided that it was fine to publish."

In addition to Dr. Coker of Livermore and Dr. Hugh-Jones of L.S.U., the 
paper's authors are Dr. Kimothy L. Smith of the Livermore aboratory, 
Patricia F. Fellows of the Army research institute, and Dr. Galena 
Rybachuck and Dr. Konstantin G. Kousoulas of L.S.U.

[Byline: William J. Broad]

--
ProMED-mail
<promed@promedmail.org>

[Dr. Coker had raised the point of multiple copies of the _B. anthracis_ 
plasmids some 3 years ago and then worked to develop the necessary QPCR 
techniques to see whether she was right. The article is entitled "Bacillus 
anthracis Virulence in Guinea Pigs Vaccinated with Anthrax Vaccine Adsorbed 
Is Linked to Plasmid Quantities and Clonality"  J. Clin. Microbiol. 2003 
41: 1212-1218 and has the necessary methodological details. Thanks to Pat 
Fellows we were able to use her USAMRIID data from a previous virulence 
study without killing any more animals and without the delay and costs 
involved. From one isolate to another, the virulence of this pathogen 
varies widely, and hopefully this paper injects some reason into that 
variance. The major objections have centered on the perceived excessive 
intracellular bulk of multiple plasmid copies. It is now up to our critics 
to prove us wrong. If it is confirmed, as I firmly believe it will be, it 
will produce an immediate boost on studies to understand the chromosomal 
contributions to virulence besides grossly simplifying virulence 
measurements in the field; up until now virulence studies have concentrated 
on the pX01 plasmid and the actions of protective antigen (PA), edema 
factor (EF) and lethal factor (LF). There was a lot of discussion 
internally and externally on publication, but we held that the future 
benefits of this research outweighed the possible costs. - Mod.MHJ]
......................................dk/mhj/pg/mpp


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