Antimicrobial peptide defenses against pathogens associated with global amphibian declines.
Global declines of amphibian populations are a source of great concern. Several pathogens that can infect the skin have been implicated in the declines. The pathogen most frequently associated with recent die-offs is a chytrid fungus, Batrachochytrium dendrobatidis. A second fungus, Basidiobolus ranarum, was isolated from declining populations of Wyoming toads. A third pathogen, Aeromonas hydrophila, is an opportunistic bacterium found in healthy frogs, but capable of inducing disease. Among the immune defense mechanisms used by amphibians is the production of antimicrobial peptides in granular glands in the skin. These packets of natural antibiotics can be emptied onto the skin when the amphibian is injured. To determine whether antimicrobial skin peptides defend against these amphibian pathogens, six peptides (magainin I, magainin II, PGLa, CPF, ranalexin, and dermaseptin), from three species, and representing three structurally different families of peptides, were tested in growth inhibition assays. We show here that the peptides can kill or inhibit growth of both fungi but not Aeromonas. Although each peptide varied in its effectiveness, at least one from each species was effective against both fungi at a concentration of about 10-20 microM. This is the first direct evidence that antimicrobial peptides in the skin can operate as a first line of defense against the organisms associated with global amphibian declines. It suggests that this innate defense mechanism may play a role in preventing or limiting infection by these organisms.
Rollins-Smith
Louise A
LA
Departments of Microbiology and Immunology and of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232, USA. louise.rollins-smith@mcmail.vanderbilt.edu
Doersam
Jennifer K
JK
Longcore
Joyce E
JE
Taylor
Sharon K
SK
Shamblin
Jessica C
JC
Carey
Cynthia
C
Zasloff
Michael A
MA
D016980:Aeromonas hydrophila / Q000187:drug effects; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology*; D001001:Anura / Q000276:immunology*; D008411:Chytridiomycota / Q000187:drug effects; D020091:Entomophthorales / Q000187:drug effects; D016905:Gram-Negative Bacterial Infections / Q000662:veterinary; D008826:Microbial Sensitivity Tests; D009181:Mycoses / Q000662:veterinary*; D010455:Peptides / Q000494:pharmacology*; D012867:Skin / Q000276:immunology*; D020096:Zygomycosis / Q000662:veterinary
D000935:Antifungal Agents; D010455:Peptides