• 13/07/2013 09:30



    Marie-Neige Cordonnier

    L’argent pourrait-il affaiblir les bactéries Pseudomonas aeruginosa (en brun sur cette micrographie), responsables d’infections nosocomiales et très résistantes aux antibiotiques ?

    © CDC / Janice Haney Carr

    Pour en savoir plus

    J. R. Morones-Ramirez et al., Silver enhances antibiotic activity against gram-negative bacteria, Science translational medicine, vol. 5, 190ra81, 19 juin 2013.


    Marie-Neige Cordonnier est journaliste à Pour la Science.

    Les propriétés antimicrobiennes de l’argent sont connues depuis longtemps : Hippocrate décrivait déjà, environ 400 ans avant notre ère, son utilisation pour faciliter la guérison des blessures. Son mécanisme d’action demeurait cependant inconnu. L’équipe de James Collins, de l’Université de Boston, aux États-Unis, vient de résoudre l’énigme. In vitro, elle a montré que les ions d’argent perturbent plusieurs processus bactériens, notamment la régulation du fer et le métabolisme. Ces dérèglements entraînent une augmentation de la perméabilité de la membrane bactérienne et de la production de dérivés réactifs de l’oxygène néfastes pour la bactérie. De plus, dans des modèles murins d’infections, ces effets augmentent l’efficacité d’antibiotiques et rendent vulnérables à une classe d’antibiotiques des bactéries qui leur résistaient. Une nouvelle piste pour contrer la résistance des bactéries ?

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  • http://blogs.scientificamerican.com/running-ponies/2013/03/30/sea-hares-thwart-spiny-lobster-attack-with-goo/


    sea hare ink secretion

    Credit: Genevieve Anderson

    The gooey ink secretions of sea hares do more than just repel or distract their predators; scientists have discovered that this sticky substance can also mask their senses of smell and taste.

    Sea hares (genus Aplysia) are large, herbivorous mollusks that are closely related to sea slugs and nudibranchs. The largest sea hare, Aplysia vaccaria, can grow up to 75 cm long and 2 kg in weight. Sea hares have a great sense of smell thanks to a pair of large sensory rhinophores that sit erect on their heads like bunny ears. Their colouring, ranging from light grey, green and red to dark purple with white spots, helps them to camouflage, as it is determined by the colour of the seaweed they eat and live nearby.

    Because they don’t have a protective shell, sea hares have equipped with a whole bunch of defence mechanisms to keep predators away from their soft flesh, which contains toxins as a last resort. They have two defensive glands in their mantle cavity; the ink gland sits on the roof of the cavity above the gill and produces a purple ink, and the opaline gland, which is located on the floor of the cavity under the gill, produces a milky white, viscous secretion called opaline. If a sea hare is threatened or attacked, a siphon inside its mantle cavity will pump one or both of these secretions out into the surrounding water. Research has shown that these secretions can act as a decoy in response to predators such as sea anemones, crustaceans and fish, leading them to misdirect their attacks. It also commonly works as a repellent, prompting tentacle shrivelling in predatory sea anemones.

    Because it is so well defended, the sea hare doesn’t have a lot of predators to worry about, but California spiny lobsters, (Panulirus interruptus) are known to take their chances on them occasionally. So in 2005, Charles Derby and Cynthia Kicklighter from the Neuroscience Institute and Department of Biology at Georgia State University in the US decided to use the spiny lobster to test the effects of the sea hare’s ink secretions. They found that the high levels of amino acids in the ink secretion mimicked the stimulatory properties of food, so when the lobsters came in contact with the secretion, they would leave the sea hare alone and try to eat the ink instead. The spiny lobsters would start “digging with the legs into the substrate covered by the secretion (“digging”) and moving the first two pairs of legs to the mouth (“grabbing”), behaviours similar to that produced when spiny lobsters are chemically stimulated to search for and sample food items”, the team reported in a 2005 issue of Current Biology (PDF). This form of chemical defence, which has a similar result to a lizard discarding its tail to distract a predator, is known as ‘phagomimicry’.  The team concluded that, ”The detection of high concentrations of free amino acids typically signals to spiny lobsters the presence of food. Sea hares exploit this property of their predator’s nervous system by releasing secretions that mimic stimulatory properties of food and thereby divert the attention of the attacker. The highly viscous nature of opaline may create a tactile sensation of food, contributing to the mimicry.”

    During this experiment, Derby and colleagues noticed that the spiny lobsters would also habitually groom their antennules (small antennae that act as the ‘nose’) and mouthparts when they came into contact with the opaline secretion, which suggested that it could be hindering their ability to taste and smell. So more recently, Derby joined Tiffany Love-Chezem and Juan Aggio from Georgia State to test if it was the chemical composition or the stickiness of the opaline secretion that was achieving this effect.

    sea hare spiny lobster

    Still from video of spiny lobster attacking a sea hare. Credit: Charles Derby et. al.

    First they extracted the water-soluble fraction of the opaline, which leaves behind the amino acids and other chemical attractants but keeps the stickiness, and painted it onto the tips of the spiny lobsters’ antennules. The lobsters were then offered delicious smelling ‘shrimp juice’ and the researchers measured the electrical activity in both their chemosensory (odour detection) and motor neurons. Reporting in Experimental Biology this week, the researchers reveal that unlike the control lobsters that had clean antennules and hence no problem sniffing out the shrimp juice, the lobsters with opaline solution on their antennules failed to get excited by food right in front of them, their chemosensory and motor neurons have been significantly reduced.

    But when the researchers applied a solution of amino acids found in opaline to see if its chemical composition affected the neuronal activity of the lobsters, they found that the lobsters reacted normally to the shrimp juice. This means that the thick, sticky texture of the opaline is the key to physically blocking the ability of the sea hare’s predator to identify it as food. “Our experiments provide strong support that the sensory inactivation is principally due to the secretion physically covering the antennule and thus blocking chemicals from accessing chemosensory neurons,” the researchers conclude. “Our experiments do not provide evidence for the chemical properties of opaline, either excitatory or suppressive, contributing to the inactivating effect, but experimental design issues allow that there might be some chemical effect that we could not resolve.”

    The researchers compare this newly discovered mechanism with a defensive behaviour found in some species of moths, whose ultrasonic emissions can ‘jam’ the echolocation of predatory bats, thereby masking the moth’s whereabouts. However, the say that this is the first time that an organism has been proven to inactivate the senses of its predators through a chemical mechanism.

    Papers cited:

    Kicklighter, C., & Derby, C. (2006). Multiple components in ink of the sea hare Aplysia californica are aversive to the sea anemone Anthopleura sola Journal of Experimental Marine Biology and Ecology, 334 (2), 256-268 DOI: 10.1016/j.jembe.2006.02.002

    Kicklighter, C., Shabani, S., Johnson, P., & Derby, C. (2005). Sea Hares Use Novel Antipredatory Chemical Defenses Current Biology, 15 (6), 549-554 DOI: 10.1016/j.cub.2005.01.057

    Love-Chezem, T., Aggio, J., & Derby, C. (2013). Defense through sensory inactivation: sea hare ink reduces sensory and motor responses of spiny lobsters to food odors Journal of Experimental Biology, 216 (8), 1364-1372 DOI: 10.1242/jeb.081828


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  • http://www.newscientist.com/article/dn23176-is-the-new-coronavirus-the-next-sars.html

    Fears a new respiratory virus identified last year in the Middle East could cause a pandemic are unfounded. The virus isn't showing signs of it – yet

    A 60-year-old man is in serious condition in hospital with the new coronavirusthat was discovered in Saudi Arabia last year. Reports that he passed it onto his son have prompted comparisons between the new virus and SARS, the disease that killed 775 of the 8000 known people it infected worldwide in 2003. But how sensible are the comparisons?

    What kind of disease does the virus cause, and can it spread?
    The man hospitalised in Manchester, UK, late last month has severe pneumonia caused by the new coronavirus – so severe, his blood is being oxygenated outside his body. The UK Health Protection Agency (HPA)reported on Wednesday that the man's son has now been hospitalised with the virus in Birmingham.

    The first man had recently travelled to Pakistan and Saudi Arabia, and fell ill after four days in Saudi. His son lives in the UK and had not been abroad – in fact he is the first of the 11 cases known so far who is not a resident of Saudi Arabia, Qatar or Jordan. The HPA says he probably caught the virus from his father.

    Does this mean the virus has the ability to spread quickly among people?
    No. The son had health issues which may have lowered his immunity, says the HPA. And no one else who has come into contact with the two has fallen sick, so far.

    Indeed, other than the son, nobody who has been in close contact with people known to be infected with the new virus have so far tested positive for it. "If novel coronavirus were more infectious, we would have expected to have seen a larger number of cases," says John Watson, head of respiratory diseases at the HPA.

    Is this the first case of person-to-person transmission of this virus?
    No. Last April, before the new coronavirus was discovered, eleven people in Jordan, including eight healthcare workers in an intensive care unit, came down with severe pneumonia. Their samples tested negative for any respiratory pathogens known at the time. But after the new coronavirus was discovered in pneumonia patients from Qatar and Saudi Arabia in September, the Jordan samples were retested. Two of the healthcare workers, who had died, tested positive for the new virus.

    The cluster in Jordan raised the possibility of human-to-human transmission, said the World Health Organization, even though not all the cases were reported as testing positive for the virus.

    This is not impossible: in the cases confirmed so far, the virus mainly affects tissues deep inside the lungs, and may not have been present in a sample from further up the respiratory tract.

    This is worrying as healthcare workers were among the chief victims of the SARS virus in 2003. Hospital workers are being closely monitored in Manchester and Birmingham.

    Three people who contracted the virus in Riyadh, Saudi Arabia, last October were also members of the same family, according to Saudi health authorities. Two died. But we do not know if these people gave the infection to each other, or if all were exposed to the same source in the environment. The results of a survey of wildlife in the region for similar viruses have not yet been released.

    Why does everyone keep mentioning SARS?
    It was also a coronavirus that caused SARS (severe acute respiratory syndrome). That virus jumped from bats to humans in southern China and spread worldwide in 2003, killing 775 people. The new coronavirus is most closely related to coronaviruses that come from bats, although that doesn't prove it is from bats or that it will do what SARS did.

    study in December found that most European health authorities have the facilities to perform a test for the new coronavirus. One problem, though, is knowing who to test. As well as being infected with the novel coronavirus, the 60-year-old man hospitalised in Manchester also had a flu virus when he was first examined. If such co-infection is common, many people with pneumonia who test positive for flu could be treated for that without being tested for any other viruses, leaving the new coronavirus to slip under the radar.

    The new virus has so far not spread widely <i>(Image: Medical rf.com/SPL)</i>

    The new virus has so far not spread widely (Image: Medical rf.com/SPL)

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  • http://www.newscientist.com/blogs/shortsharpscience/2013/01/londons-boris-turns-turtle-get.html

    Douglas Heaven, reporter


    Up a bit... left a bit... a bit more... ah, that's the spot. (Image: Mikael Buck/Rex Features)

    Named after his adoptive father, London mayor Boris Johnson, Boris the green turtle doesn't get a tickle from the cleaner every day. The divers above are taking part in Sea Life London Aquarium's annual January "Deep Clean", in which tanks and inhabitants get a good scrub.

    Despite being capable of breath-holding dives of over 10 hours - the longest of any vertebrate - green turtles are usually found in shallow lagoons in the warmer parts of the Atlantic and Pacific Oceans. But every three to four years they swim thousands of kilometres from their regular foraging grounds to remote beaches where they mate and the females lay eggs in holes in the sand. Hatchling turtles then face a desperate race to the relative safety of the sea while birds, crabs and other predators pick off the stragglers.


    Those that make it to adulthood have been shown to have an amazing homing ability - possibly guided by smell. Not only do they return to their own birthplace to breed, but they can retrace exact routes across an ocean to favoured feeding sites.

    Though some have questioned green turtles' endangered status, sea turtles generally don't have it easy. As well as animal predators, baby turtles must also now contend with changing weather and human interference.

    London Aquarium staff hope that Boris junior's new family connection will help raise awareness of their plight. "I hope he's got a thick skin," said Boris (the mayor).

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