Indoor dust carrying bacteria that could be harbouring antibiotic resistance
The basis of the bandage is colorimetry. 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.
If the bandage becomes red, the researchers will pass light through the bandage, which stimulates the production of reactive oxygen species from a metallo-organic compound called PCN-224, built on a porphyrin base, and which has high photodynamic properties, releasing a flood of ROS in response to light. These inhibit or weaken the bacteria, increasing their susceptibility to the drug. Thus, the bandage has been proved to accelerate wound healing in mice after introducing both drug-sensitive and drug-resistant bacteria into the wounds. The experiment
The researchers incorporated all these elements into a cellulose sheet from which they produced the PBA. They then carried out a proof-of-concept experiment to test whether the PBA could sense drug-sensitive and drug-resistant Escherichia coli ( E. coli ) in the wound and treat it. Mice with wounds on their back were used. The wounds were infected with drug-sensitive and drug-resistant E. coli , respectively, and the PBA was used to treat the wound for 4 hours. Escherichia coli bacteria close up. Image Credit: Dreamerb / Shutterstock The findings
The experiments showed that the PBA over the wound infected with drug-sensitive E. coli turned yellow, proving that this senses the infection very well. The survival of these microbes was reduced markedly in the wound treated with PBA. The wound was almost fully healed on day 3, showing that the ampicillin was enough to heal this infected wound. The irradiated wounds in this category were, however, swollen, showing that the ROS could have caused auxiliary damage.
In the other group, the PBA turned red, showing that drug resistance was sensed well. Moreover, a combination of ROS-based PDT and PBA produced better healing in these wounds. Real-time testing on infected tomatoes showed the usefulness of PBA in picking up drug resistance, and the need to use PDT when drug resistance was sensed. Conclusion
This highly innovative all-in-one system provides a means of visualizing infection, sensing drug resistance, and selectively applying antimicrobial therapies based on the type of organism (drug-sensitive or drug-resistant). This allows real-time monitoring of drug resistance, minimal off-target side effects, avoids the need for microscopy and saves precious time. The time taken for this sensing was only 2-4 hours, and it could pick up 104 CFU/ml, in the case of drug-resistant E. coli – a highly acceptable limit for clinical use. The high performance, the low cost and the ease of use make it a very appealing application for point-of-care treatment. Journal reference:
Yuhuan Sun, Chuanqi Zhao, Jingsheng Niu, Jinsong Ren, and Xiaogang Qu. Colorimetric band-aids for point-of-care sensing and treating bacterial infection. ACS Central Science. https://dx.doi.org/10.1021/acscentsci.9b01104 .
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