How researchers discovered medical leeches were causing antibiotic-resistant infections: 10 things to know

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On Dec. 13, 2012, a medical team at The University of Iowa Hospitals and Clinics in Iowa City administered medical leeches, along with the antibiotic ciprofloxacin, to a patient with failing facial skin grafts. Two weeks later, the patient developed an antibiotic-resistant infection due to the leeches being cipro-resistant. A study published July 24 in mBio takes a deep dive into these types of medical cases, investigating the connection between leeches and antibiotic resistance.

Here are 10 things to know:

1. The FDA permits the use of medical leeches for venous congestion only after certain surgeries, such as skin grafting, according to STAT. Hospitals turn to leeches when blood is able to flow to a patient's arteries, but cannot flow through the veins, causing the skin to swell, harden and eventually die.

2. Surgeons give patients antibiotics before administering leeches to protect them from bacteria within the leeches' stomach. Leeches are starved for months so they can suck blood from the wound for up to 15 minutes at a time and, in the process, turn the patient's formerly swollen, almost dead skin to a healthier color.

3. Only two manufacturers are currently licensed to sell leeches with the intent for therapy in the United States: France-based Rimcarimpex and Wales-based Biopharm Leeches, which respectively ship an estimated 80,000 and 20,000 leeches to the U.S. a year.

4. To assess the link between leeches and antibiotic-resistant infections, Bradley Ford, MD, PhD, director of microbiology at the University of Iowa Hospital and Clinics, sought out specialist Joreg Graf, PhD, associate professor of molecular and cell biology at the University of Connecticut in Harford and his PhD student Lidia Beka who were studying leeches and the bacteria in their guts.

5. The researchers put out a request for samples of the bacteria and received mailed-in samples from pus or the surgical instruments used on leech therapy patients from healthcare facilities in Iowa, Missouri, California and France. They began sequencing the leeches' DNA looking for any historical patterns.

"In 2013 and 2014, in four different shipments, 95 percent of the strains had this resistance marker," Dr. Graf, lead author of the mBio study, told STAT. "We go back to 2011 and 2009, it’s less than 1 percent."

6. When they received their test results from the leeches between 2013 and 2014, the gut samples showed traces of cipro, also containing enrofloxacin, a veterinary drug, which becomes cipro when metabolized.

7. Ms. Beka also fed the leeches two strains of bacteria at once to see how the leeches would hold up with different amounts of antibiotics. When no drug was present, the susceptible bacteria appeared, but when the antimicrobials formed a level traceable inside the leeches, antibiotic resistance was activated.  

8. Dr. Graf and Ms. Beka created a family tree of the general leeches, mapping the antibiotic resistance of the gut bacteria within the samples sent in from California, France and Iowa. They found the gut bacteria had become stronger due to careless overflow of drugs within their environment. The source of the enrofloxacin is still unclear.

"In Europe, there was the fear, after bovine spongiform encephalopathy that it was dangerous to give cattle blood to leeches, so in Germany they switched to using horse blood, and in France they probably switched to poultry blood. Enrofloxacin is approved for veterinary use in poultry," said Dr. Graf, who also serves as a consultant for a German leech farm, which is not approved by the FDA to sell leeches for therapy in the U.S.

9. Brigitte Latrille, the director of Rimcarimpex, told STAT in an email that no agency has ever contacted her about switching away from cow blood, although she's fed her leeches chicken blood since 2001. Rimcarimpex also tests every one of its leeches for antibiotic-resistant bacteria before they get sold. When asked how long those tests have been going on and whether she knew how the cases of antibiotic-resistant infections came about, Ms. Latrille did not reply to STAT.

10. Based on the study findings, researchers suggest using a different antibiotic when administering leeches to patients.

More articles on clinical leadership and infection control: 

3-pronged intervention improves intraoperative antibiotic redosing compliance
10 recent findings on antibiotic stewardship and resistance
Superbugs drive new antibiotic developments from the dirt

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