New approaches to the management of debilitating diabetic foot ulcers may be on the horizon, thanks to new microbiome research. Today at the Society for General Microbiology Annual Conference, Eleanor Townsend from the University of the West of Scotland is outlining the first comprehensive analysis of the range of bacteria found in the diabetic foot ulcer microbiome.
Diabetes is on the rise, affecting at least 3.2 million people in the UK. Along with the immediate problem of managing blood sugar, there are several very serious complications that can occur.
Severe skin ulcers are one of the worst problems faced by patients with diabetes. These chronic open wounds are typically on the foot or lower leg, can be extremely difficult to treat, easily become infected and can get so severe that it is necessary to amputate the affected limb.
Researcher Eleanor Townsend explained, “In the worst cases, the dead tissue [in these ulcers] goes all the way down to the bone. It’s a huge challenge for diabetes clinics to manage such intractable wounds and they require a three pronged attack: antimicrobial treatment; removal of dead, damaged, and infected tissue; and high-tech dressings.”
The doctors, nurses, podiatrists and other professionals tasked with managing infected diabetic foot ulcers have to be innovative and individually tailor treatment to each patient. These treatments are usually based on close monitoring of interventions to see what works best for that person. “It’s a bit better than trial and error,” Eleanor said, “but knowing where to start is a problem – it tends to be a case of starting broad and focusing in.”
All this could change, thanks to Eleanor and her colleagues, who have uncovered the range of bacteria species present in diabetic foot ulcers. This knowledge could improve the specificity of treatment and the outcomes of patients, for the better.
Previous studies of diabetic foot ulcers have relied on growing bacteria from swabs, in the lab. This tends to bias results towards common skin and water bacteria that are easy to culture, such as Streptococcus, Staphylococcus, and Pseudomonas. Treatments, it then follows, have typically included antimicrobial drugs that act mainly against these species.
Eleanor’s work has uncovered a previously unknown threat, lurking deep in the infected tissues of diabetic foot ulcers – bacteria that require a very low oxygen environment to grow. Known as anaerobes, these bacteria are difficult to grow under laboratory conditions and so they didn’t show up in earlier studies. There was also the problem, as Eleanor explained, that expert microbiologists carrying out earlier studies rarely did the swabbing themselves. This time, the microbiologists visited the clinic and, like the best wine tasters, their well-practiced noses smelled the anaerobes straight away.
“It’s hard to describe the smell of anaerobic bacteria but when you know it, it’s hard to miss! They can be quite pungent, ranging from sweet and musky through to fishy and acrid. We heard of a patient who had been asked not to visit their local pub because the smell of their ulcers was so bad.”
To get a more accurate picture of the diabetic foot ulcer microbiome, the research team took swabs from patients and extracted the DNA from every microbe that was picked up. They then sent the DNA off to a specialist company that could tell them which species were present.
Between just 16 patients, Eleanor has found 216 unique species and sub-species. “We expected to find typical skin bacteria but there were some weird and wonderful species in there – about two thirds of them, I’d never even heard of before starting my PhD research,” she said.
One patient had a total of 86 different bacterial species in their ulcer, while the least diverse microbiomes comprised of around 20 species. As well as the previously identified bacteria, the ulcers also harboured species associated with the human gut and with soil. “It seems that ulcers provide such a perfect environment that getting the wound dirty just once could be enough to establish some of these species,” Eleanor explained.
Armed with this knowledge, the health professionals treating diabetic foot ulcers have a far better chance of success in the battle against infection because treatments can be targeted at the organisms most likely to be present.
This isn’t the end of the story though. One of the most interesting aspects of the bacteria in diabetic foot ulcers is that they form biofilms – three dimensional communities that are self-supporting, with each species of bacteria fulfilling its own particular niche. These structures are very difficult to clear completely with antibiotics. So the next step in this research is to recreate the biofilms in the lab and use them to test potential new drugs, dressings and treatment strategies.
Nancy is a freelance science writer www.nancywmendoza.co.uk