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Honey bee larvae
infected with American foulbrood become a stringy mass of material that later
dries and carries the spores that may infect other larvae. Click the image
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Gene Helps Explain Foulbrood's Spread Among U.S.
Bees
By Alfredo
Flores July 17, 2007
A gene for resistance to tetracycline drugs has been discovered in the
microbe that causes the bacterial disease American foulbrood (AFB) in honey
bees, according to scientists with the Agricultural Research Service (ARS).
AFB, caused by the spore-forming Paenibacillus larvae
bacterium, is so serious that infected colonies must be burned—an
extremely costly option for beekeepers.
From the 1950s until very recently, the only AFB treatment approved
for use in the United States has been the antibiotic oxytetracycline (OTC),
sold under the name Terramycin. But recently there have been reports of P.
larvae suddenly developing resistance to Terramycin.
At the
ARS
Honey Bee Research Unit, Weslaco, Texas, molecular biologists
Dan
Murray and
Katherine
Aronstein have discovered a natural plasmid in P. larvae—called
pMA67—that contains an OTC-resistance gene. Plasmids are small DNA
molecules containing up to several dozen genes that bacteria pass on when they
reproduce. This is the first report of any tetracycline-resistance gene being
found in any Paenibacillus bacteria.
In tests on 36 P. larvae strains gathered from across the
United States and Canada, all 21 OTC-resistant strains were found to possess
the pMA67 plasmid, and all 15 OTC-sensitive strains did not.
Two explanations for the rapid spread of OTC resistance are thought to
be likely. First, bees from broad geographical areas are brought together when
beekeepers rent their hives to agricultural producers for pollination. This
provides the opportunity for OTC-resistant bacteria to spread among bees that
otherwise wouldn’t encounter them.
Second, it appears, based on its DNA sequence, that plasmid pMA67 has
the ability to move into other bacterial cells through a process called plasmid
mobilization. In this process, copies of pMA67 are physically transferred to
other bacterial cells that they come in contact with.
Read
more about the research in the July 2007 issue of Agricultural
Research magazine.
ARS is the U.S. Department of
Agriculture’s chief scientific research agency.
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