Quaternary ammonium carbon quantum dots as an antimicrobial agent against gram-positive bacteria for the treatment of MRSA-infected pneumonia in mice

In this work, quaternary ammonium carbon quantum dots (QCQD) was successfully synthesized with 2,3-epoxypropyltrimethylammonium chloride and diallyldimethylammonium chloride by a simple green “one-pot” method. QCQD was demonstrated to have satisfactory antibacterial activity against gram-positive bacteria, including Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Listera monocytogenes and Enterococcus faecalis. QCQD was used to treat MRSA-infected pneumonia in mice, and could promote the regression of pulmonary inflammation in lung of mice. In vivo and in vitro toxicity tests also confirmed that QCQD had acceptable biocompatibility. There is no doubt that all the experimental results confirmed that QCQD is a promising antimicrobial agent for treating infections of gram-positive bacteria. The antibacterial mechanism of QCQD was analyzed and confirmed by the quantitative proteomics based tandem mass tags, revealing that QCQD might interfere with the protein translation, posttranslational modification and protein turnover in bacterial cells by mainly acting on ribosomes and upregulating RNA degradation related proteins. The application of proteomics extended the research on antibacterial mechanism from single target to protein network and realized the research and analysis on multiple targets of bacteria treated by QCQD, providing a new idea and strategy for the development of efficient bactericidal weapon against drug-resistant bacteria.