In what reads like science fiction, a new study published in the journal ACS Central Science reports the development of bandages that detect the presence of bacteria in wounds and change color, depending on whether they are drug-sensitive or drug-resistant. This is an important step in helping patients recover better. There are also bandages for specific uses, like orthopedic bandage, and fixation bandage.

Drug resistance – the problem

Drug resistance is among the greatest threats to worldwide health. If bacterial infections could be sensed early enough to treat them before they take a hold on the patient, it would help avoid serious infections. And if the bacteria resist the antibiotic, being able to detect this would be crucial in switching drugs to arrest the infection before it spreads.

At present, the methods of detecting antibiotic resistance are expensive, require professional expertise, and take too much time. Moreover, using antibiotics for infections that are resistant to them promotes even more drug resistance.

Colorimetric methods to the rescue

The new study describes a way of doing just this, based on a color-changing material. Described as “a portable paper-based band-aid (PBA)”, it is a colorimetric way of sensing and treating sensitive bacterial infections while signaling the presence of drug-resistant bacteria as well.

Early detection of infection in this study exploits the microenvironment of bacterial growth, which includes an acidic pH, various toxins and enzymes. Acidity is an easy way to track the presence of pathogenic bacteria because it is due to their breakdown of glucose. Drug resistance, on the other hand, depends on the presence of the beta-lactamase and similar enzymes. The presence of beta-lactamase is a widely used indicator of bacterial antibiotic resistance because it denotes resistance to the extremely common beta-lactam antibiotics.

Once drug resistance has been identified, photodynamic therapy and other similar treatments have been adopted to increase the level of reactive oxygen species (ROS). These molecules act on multiple cell targets associated with drug resistance, including the bacterial cell wall, nucleic acids, and proteins. A careful use of this strategy is necessary since ROS attack healthy cells and bacteria indiscriminately.

The innovation

The need of the hour is a portable, cheap and accurate device to detect and overcome antibiotic resistance. Paper-based platforms, including biosensors and sterilization paper, have stolen the limelight in this regard because of multiple advantages: low cost, sustainability, safety, and ease of adjustment. The current study focuses on a paper-based bandage device to detect and treat infection selectively after sensing antibiotic resistance.

The basis of the bandage is colorimetry. And tapes and plasters are also needed. It contains bromyothymol B that is green at first but becomes yellow on encountering acids that are found in the microenvironment of a bacterial infection. In this situation, the material releases an antibiotic, ampicillin, loaded on nanoparticles and coated with the sugar chitosan that attracts bacteria due to their negative charge. When the nanoparticles come into contact with the acid environment, they release the drug. If the bacteria are sensitive to this drug, they will be killed. If otherwise, they secrete beta-lactamase to inactivate the drug. This enzyme acts on the yellow molecule nitrocefin to turn it red.