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Subject:
From:
Peter L Borst <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Fri, 28 Nov 2008 12:56:33 -0500
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Antimicrobial Defense and Persistent Infection in Insects
Eleanor R. Haine, et al
http://www.sciencemag.org

> During 400 million years of existence, insects have rarely succumbed to the evolution of microbial resistance against their potent antimicrobial immune defenses. We found that microbial clearance after infection is extremely fast and that induced antimicrobial activity starts to increase only when most of the bacteria (99.5%) have been removed. Our experiments showed that those bacteria that survived exposure to the insect's constitutive immune response were subsequently more resistant to it. These results imply that induced antimicrobial compounds function primarily to protect the insect against the bacteria that persist within their body, rather than to clear microbial infections.

> Constitutive defenses, including haemocytes and cytotoxic enzyme cascades, are responsible for "frontline" physiological defense against microbial insults. Our observations imply that induced antimicrobial effectors do not function to clear bacteria, but rather "mop up" those that have survived selection via the host's constitutive defenses ... recent work on Drosophila melanogaster showed that haemocytes, rather than antimicrobial peptides, are responsible for the protection against secondary infection.


Comment:

This study describes antimicrobial response in insects as the last
line of defense.  In essence, insects use IPM in employing a tiered
response saving the most toxic and possibly most effective responses
for the last resort. This probably helps to prevent invading microbes
from developing resistance to these, but also may reflect the
additional metabolic cost as well as the potential harm that such more
sophisticated and toxic responses may inflict on the very organism
that delivers them.

pb

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