Hi all,
I have been following this thread with interest.  Here are some
thoughts on the issue.
First Nick is right oxytetracycline  the antibiotic in terramycin
(TM) does indeed break down rather quickly in the presence of warmth,
moisture, or sunlight.  This is the main reason that residues have
not been found in honey from colonies with the drug in the hive
during honey production.  In the US the label for use in beehives
requires that it be removed 4 weeks before the honeyflow as an added
precaution.  Some other drugs do not break down as quickly and
therefore are much more likely to contaminate harvested honey.
 
I suspect that it is the short life of active TM in the hive when it
is administered as a dust with powdered sugar that has helped prevent
the emergence of drug tolerant or resistant strains of Bacillus
larvae in North America.  If a beekeeper is using TM and finds a
colony with AFB the colony should be destroyed as it could be drug
resistant.  It may not be but why take the risk.  I agree with Allen
that the widespread occurrence of such strains would have an impact on
international trade in honey.
 
Drug resistance appears when the drug selects for those few resistant
members or the bacterial population by elimination their competition.
The resistant stains become the dominate strains over time in the
presence of the drug.  These few resistant bacteria are already
present in the population.  The main factor in selecting for these
resistant individuals is the presence of the drug in their
environment for a long period of time ( in terms of generations of
bacteria ).  So if one wanted to develop resistant strains of a
bacteria they would keep the drug present in an active state for a
long time.  About the only way of doing this with TM in a honey bee
broodnest that I can think of is to protect the TM from moisture by
mixing it with vegetable oil.
 
My view is that TM is a valuable tool in cleaning up and dealing with
AFB but we do need to use it wisely.  All infected combs with scale
should be destroyed by rendering, burning, or burying.  TM is very
helpful for cleaning up comb and equipment that has been exposed to
AFB but does not contain scale.  If you use TM and find AFB in a
colony it is cheaper and simpler to just destroy the colony and
therefore destroy a potential resistant strain that to try to clean
it up.  If other drugs are used, you are spreading the resistant
strain.  In other bacterial diseases, resistance to multiple drugs
usually develops more quickly that resistance to the first drug so
the use of alternate drugs may not buy much time.
 
There are many things we as beekeepers can do to limit the spread of
AFB and deal with it in our operations in addition to the use of TM.
The main thing is to remember that any time you are moving broodcombs from
one colony to another you may be moving scale.  Many of our
beekeeping brothers and sisters in other countries where they don't
have the access we do to TM can give us in North America some ideas
on how to deal with AFB economically without using TM and it would be
good to hear from them.
 
blane
 
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Blane White
State Apiary Inspector
Minnesota Department of Agriculture
90 W Plato Blvd
St Paul, MN 55107
http://www.mda.state.mn.us
phone 612-296-0591
fax 612-296-7386
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