As unspent antibiotics pass from our bodies into the environment, they contribute to the development of antibiotic-resistant bacteria. Scientists are addressing this problem with a new technology which causes such drugs to only become active upon exposure to green light.
Ordinarily, when antibiotics are administered orally, much of the still-active medication is simply passed in our urine without ever being taken up by the body.
Sewage treatment plants are only partially effective at removing these drugs from the waste stream, allowing significant concentrations to enter the waterways. There, they interact with harmful bacteria already present in the environment. Those microbes respond by evolving a resistance to the antibiotics, thus making them harder to kill when they infect us.
Seeking a solution to this problem, a team at The Netherlands' University of Groningen set about developing a method of keeping antibiotics inert until they're triggered by exposure to a specific color of light. That light could be administered solely at the infection site in a patient's body, causing the drugs to only kill bacteria at that place and time.
The scientists started with a molecule derived from the natural compound coumarin, and chemically linked it to the component of penicillin that kills bacteria by destroying their cell walls. As long as that coumarin molecule is bound to the drug, which is known as Penicillin-PPG (Photocleavable Protecting Groups), the antibiotic remains inactive.
The one thing that does cleave the molecule from the drug is exposure to green light. Once this has occurred, the Penicillin-PPG is activated, eradicating bacteria that are present in the irradiated region. The green light could be administered externally if the infection site isn't too deep within the body, or administered internally via an endoscope.
In lab tests, Petri dishes containing Penicillin-PPG-doped agar were inoculated with E. coli bacteria, then half of each dish was covered with a light-blocking aluminum sticker. The dishes were subsequently exposed to green light for one hour, after which they were left to incubate overnight. By the next morning, bacterial cultures were present on the aluminum-covered side of each dish, but were absent from the exposed side.
Further testing showed Penicillin-PPG to also be effective at preventing the growth of Staphylococcus epidermidis bacteria, and at treating Staphylococcus aureus infections in wax moth larvae (which have an immune system similar to that of humans). As an added bonus, PPG versions of antibiotics should also reduce unwanted side effects, as the drugs will only be active in the part of the body where they're needed.
"Controlling drug activity with light will allow precise and safe treatment of localized infections," says Prof. Wiktor Szymanski, a corresponding author of the study. "Moreover, the fact that light comes in different colors gives us the ability to take the spatial control of drug activity to the next level."
A paper on the research, which was led by Prof. Albert Schulte and Dr. Jorrit Schoenmakers, was recently published in the journal ACS Central Science.
Source: American Chemical Society
