It’s a tidy room, bright and cheerful despite its display of bowls and knives for bleeding, leech jars with perforated lids, and oil paintings of patients with leeches stuck on their necks. He speaks of a “veritable pharmacy” of leech products, referring to potentially useful compounds he and his researchers have turned up. There’s the enzyme orgelase, a “spreading factor” that quickly distributes chemicals in leech saliva around the wound. Sawyer believes it could help carry local anesthetic deep into tissues before surgery. And there’s calin, which neutralizes the effects of collagen, a natural blood clotter. He calls it a “collagen-coating paint” that could help prevent blood clots following vascular surgery. Sawyer and others have isolated a dozen more active substances fromHirudoand nine other leech species.
Finding such a substance could lead to a way of controlling staph growth in humans. But leeches themselves may prove a direct source of antibiotics. In leeches, these peptides are produced within 15 minutes of a bacterial infection. “These antimicrobial peptides diffuse quicker and easier than antibodies,” he says, suggesting that such speed and potency might add up to a defense that can outbreed and outrun pathogens.
Within two to four weeks, about 15 to 25 leeches hatch. Under the right conditions, a leech can produce up to 1,200 young in a five-year lifetime. At Biopharm, leeches feed on pig blood poured into an artificial membrane that simulates the skin of natural prey. After rearing the leeches for six months at 80 degrees Fahrenheit, Peters transfers them to a room chilled to a growth-slowing 45 degrees.
Immature leeches feed on the thin-skinned bodies of amphibians and young fish; mature leeches can move on to larger prey, such as cattle, horses, ducks, and humans. The leech’s natural anticoagulant, hirudin, keeps blood flowing for the 20 to 40 minutes it takes to feed, during which time the leech’s body weight may increase 10 times, reaching up to 60 grams . The secretions of one leech can prevent up to half a cup of blood from coagulating. Blood sucked into its crop can take 18 months to digest. During this time, the leech does little but lie around in a stupor, rousing itself only to reproduce. The hermaphroditic leech copulates on land, wrapping around its partner using a kind of mucus, and later secretes a cocoon, which it deposits in damp soil near the shoreline.
“Antibacterial peptides from leeches may cure human diseases,” Salzet says. Courtly and soft-spoken, the North Carolinian escorts a visitor through his leech museum.
In nature, the medicinal leech inhabits the wetter environments of western and southern Europe. Sensing the warmth, motion, or shadow of possible prey, the leech cozies up, attaches itself with its suckers, injects an anesthetic so that its presence is not detected, and goes to work. The three jaws of its head sucker stiffen, protrude, and slice into the prey’s skin with a sawing motion.
When leeches leave Biopharm—thousands a year—they are packed like Chinese takeout in little cardboard boxes. They go to such places as Carolina Biological Supply, in Burlington, North Carolina, where workers store them in buckets of icy spring water until a surgeon like Levin calls. “We maintain them so that when surgeons get one, it’s a nice, clean, hungry leech,” says Lawrence Wallace, the firm’s director for live biological products. In the gut of every one, even those raised in sterile conditions, livesAeromonas hydrophila,a bacterium that prevents putrefaction of the leech’s blood meal and supplies enzymes crucial to its digestion. Studies have found that as many as 20 percent of leeched patients become infected by this bacterium, which increases the risk of serious wound infections. So preventive antibiotics are given to patients with weakened immune systems.Aeromonasalso kills other bacteria. This may be the result of inhospitable conditions within the leech, says Graf, but it’s also possible thatAeromonasproduces something that inhibits staph growth.
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