Dextran-coated gold nanoparticles for the assessment of antimicrobial susceptibility.

Bacteria rapidly evolve mechanisms to become resistant to antibiotics. Therefore, identifying an effective antibiotic or antibacterial agent and administering it at concentrations that will successfully prevent bacterial growth (antimicrobial susceptibility) is critical for health care decision making and vital for the battle against multi-drug-resistant bacteria. Currently, the determination of antimicrobial susceptibility requires at least 24 h. Herein, we describe a nanoparticle-based antimicrobial susceptibility assay based on the concanavalin A-induced clustering of dextran-coated gold nanoparticles, which sense the presence of available complex carbohydrates in bacterial suspension. Under conditions of bacterial growth inhibition, addition of concanavalin A results in the formation of extensive dextran gold nanoassemblies, which are facilitated by the presence of free carbohydrates in solution and result in large shifts in the surface plasmon band of the nanoparticles. Meanwhile, at conditions of increased bacterial growth, a decrease in the amount of free carbohydrates in solution will occur due to an increased carbohydrate uptake by the proliferating bacteria. This will result in a decrease in the size of the gold nanoparticle clusters and an increase in the number of nanoparticles that bind to bacterial surface carbohydrates, causing lower shifts in the plasmonic band. The gold nanoparticle-based assessment of antimicrobial susceptibility yields results within 3 h and can be used for the high-throughput screening of samples during epidemics and identification of potential antimicrobial agents to expedite clinical decision-making in point-of-care diagnostics.