Frog skin fights 'superbugs'

Infection by antibiotic-resistant pathogens is becoming increasingly widespread in hospital and community settings. Many researchers have begun to study naturally occurring antimicrobial peptides (AMPs) as a potential treatment for these diseases. AMPs, which are produced by a variety of multicellular organisms, directly damage the bacterial membrane. As a result, microbes acquire resistance to these molecules more slowly than they do to conventional antibiotics.

In a study led by Giovanna Batoni of the Sapienza University of Rome (Italy), researchers isolated five AMPs (temporins A, B and G, Esc(1–18) and bombinin H2) from the skin of two species of frog and one toad (Antimicrob. Agents Chemother. 52, 85–91; 2008). They examined the effects of these peptides on five bacterial species that are commonly involved in hospital-acquired infections, as well as on several emerging pathogens. When tested in buffer, all AMPs killed the bacteria, though they differed in potency and mechanisms of action.

When tested in human serum, which is known to inhibit the effects of AMPs, all of the peptides had bactericidal effects against Gram-positive species. Only Esc(1–18), however, was able to substantially affect Gram-negative bacteria in the presence of serum.

Mole-rats can take the heat

Sensitivity to pain is generally consistent across vertebrates: most stimuli that would cause pain in humans are also painful to other animals. A new study led by Thomas Park of the University of Illinois at Chicago and by Gary Lewin of the Max-Delbrück Center for Molecular Medicine (Berlin, Germany) shows that, at least in some respects, the African naked mole-rat may be an exception to the rule.

When the team exposed mole-rats to capsaicin, the ingredient in chili peppers that causes an intense burning sensation in humans, the rodents did not show a pain response (PLoS Biol. 6, e13; 2008). Mole-rats were also insensitive to acid injected subcutaneously and did not show thermal hyperalgesia, in which inflamed areas of the skin are more sensitive to extreme heat.

In a previous study, the group discovered that mole-rats do not produce substance P, a compound involved in transmitting pain impulses to the central nervous system. By inducing production of this compound, the researchers showed that they could 'rescue' mole-rats' sensitivity to capsaicin and cause thermal hyperalgesia.

Researchers believe that a better understanding of substance P could provide insight into chronic pain in humans and may aid in the development of new analgesic drugs.

Communication, not camouflage, drives chameleon change

Color change in chameleons can serve at least two purposes: signaling to other chameleons and hiding from potential predators. New research from Devi Stuart-Fox (University of the Witwatersrand, South Africa, and The University of Melbourne, Australia) and Adnan Moussalli (University of KwaZulu Natal, South Africa, and Museum Victoria, Melbourne, Australia) has established that social signaling, rather than camouflage, drives the evolution of this color change.

Stuart-Fox and Moussalli used field-based behavioral trials to quantify color change in 21 lineages of southern African dwarf chameleons (Bradypodion spp.). The capacity for color change varies markedly among lineages; some show only shifts in brightness (different shades of one color), whereas others have prominent chromatic changes (including many different colors).

The results indicated that species with the greatest capacity for color change had display signals that were conspicuous to other chameleons because of contrast against the environmental background and against adjacent body parts (PLoS Biol. 6, e25; 2008). In addition, the capacity for color change was not related to the variation in environmental background that chameleons would need to match in order to camouflage themselves. Overall, the research suggests that color change in some chameleon species evolved as a strategy to facilitate social signaling rather than camouflage.