The Next Magic Bullet Antibiotic May Come from Roadkill
Our quest to find new antibiotics has taken a turn — a turn down the road, that is. A team of scientists from the University of Oklahoma is scooping up roadkill and searching for bacteria on them that might yield the world's next antibiotic.
The research — which discovered a potential antibiotic found in the ear of a dead opossum — was led by OU's Robert H. Cichewicz, principal investigator of the Natural Products Discovery Group and director of the Institute for Natural Products Applications and Research Technologies, and was published in the Journal of Natural Products.
Roadkill might seem like an unlikely reservoir of antibiotics, but there is solid reasoning behind their choice.
Everyone, humans and animals included, has a community of bacteria that lives in and on them. Part of this community includes normal bacteria that don't cause infection, but protect us from other disease-causing bacteria. Some strains of Escherichia coli, for example, produce toxins called colicins that kill other kinds of E. coli.
The scientists hypothesized that they could find some of those protective bacteria, isolate compounds from them, and some would prove to have antibiotic properties. And because they wanted to find the most diverse types of bacteria, they thought of animals — but not just any lab animal — wild animals, with the potential to have encountered and carried many different types of bacteria.
Since wild animals are hard to capture, they sought and received permission from the State of Arkansas to get a scientific collectors' permit to analyze roadkill for their study.
These adventurous researchers swabbed the ears, eyes, mouths, noses, GI tracts, and rectums of armadillos, deer, opossums, raccoons, squirrels, and skunks. Yes, even dead skunks. Then they isolated bacteria and grew them in the laboratory, after which they purified chemicals produced by the bacteria and identified the genes that produced them. After that, they looked at the chemicals' ability to kill or inhibit the growth of bacteria and yeast.
Opossum carcasses were the most frequently encountered roadkill, and they proved to be a rich source of bacteria, too. Of the 3,659 types of bacteria isolated from the animals, 39% (1,425) were isolated from opossums.
They also yielded the most promising compound. Two different bacteria, Pseudomonas and Serratia, found in the ear of an opossum, produced compounds that inhibited the ability of Candida albicans yeast to form a biofilm.
Biofilms — a network of physically closely associated bacteria usually attached to a surface — are one way disease-causing bacteria thrive and establish infections. The compounds did not kill the yeast, but biofilms are sources of human disease, so being able to inhibit them is important.
The technique used by the scientists allowed for a fast way to acquire and screen for thousands of bacterial compounds quickly and easily. If the molecules end up being medically useful, the methods used in this study could be used to harness their genes to manufacture them in large quantities. And not a moment too soon.
We aren't just in a rush, we are officially in urgent mode. The dwindling supply of antibiotics effective against certain powerful bacteria is fueling the creative pursuit to find alternatives — anywhere.
Last month, the World Health Organization published a list of the 12 bacteria for which antibiotics are urgently needed. These represent multi-drug resistant bacteria where we are running out of antibiotic treatment options. Most of these pose particular infection threats in hospitals, nursing homes, and among patients who use devices like ventilators and blood catheters.
The reasons bacteria are rapidly developing resistance to most of the drugs in our arsenal of antibiotics are many. One reason is because the use of antibiotics themselves promote resistance — they kill the sensitive bacteria and the only ones that are left to live and thrive are the ones that are resistant to the antibiotic.
Another reason is overuse and misuse of antibiotics. When antibiotics are prescribed for viral illnesses or when the bacterial cause has not been identified, exposure to antibiotics of any bacteria present can cause them to develop resistance.
Since so many people in hospitals and care facilities are treated with antibiotics, those places become a rich source of antibiotic-resistant organisms, where they can readily infect the sickest patients.
The Centers for Disease Control and Prevention estimates that at least two million people become infected with antibiotic-resistant bacteria every year in the US, and at least 23,000 people die as a direct result of those infections.
We can expect ten million deaths a year globally from antibiotic resistance by the year 2050, or about 350 million deaths, according to the Review on Antimicrobial Resistance, commissioned by the UK Prime Minister. That's over four percent of the current world population — and that prediction is enough to set fire to scientists, like Cichewicz and his team, motivated to solve the problem before the predictions come true.