Time-Resolved Single-Cell Lysis Kinetics of Metal Nanoparticle-Infused Biopolymer Matrices

Abstract

Bacterial infections continue to be a growing concern in healthcare facilities due to the increasing number of multi-drug resistant bacteria. The extensive use of antibiotics has weakened the potency and effectiveness of these drugs, consequently promoting bacterial infections and extending healing time. Therefore, there is an immediate demand to find an alternate method to combat the spread of bacterial infections. Metal nanoparticles (MNP) have proven to be an effective antibacterial agent against antibiotic-resistant bacteria, and when incorporated into polymeric substrates, have exhibited high toxicity towards bacterial cells. Current research proposes that MNP interact with the bacterial cell wall, undergo redox processes to form ions, and the ions diffuse into the cell resulting in disruption of membrane-bound proteins. This results in the inhibition of cell replication or cell lysis. However, existing methods of antimicrobial susceptibility testing, such as broth dilution assays and disk diffusion, fail to provide a greater understanding of the time scale required for the single cell lysis process to occur. More specifically, the conventional methods have substrate and agent limitations, as well as assume homogeneity in the bacterial population, therefore making the techniques an ineffective method for probing the cell lysis mechanism of MNP-infused biopolymer matrices. To further investigate the mechanistic action of metal nanocomposites, this research utilizes epi-fluorescence optical tweezers for antibacterial characterization. More specifically, a single E. coli cell was optically trapped, non-covalently docked to MNP-infused alginate matrix, and the cell viability kinetics were monitored in situ. Initial results showed that antibacterial activity of Cu and Ag functionalized nanocomposites was related to the metal concentration and size of colloidal NP. Ag incorporated polymers exhibited greater antibacterial effectiveness when compared to Cu potentially due to the role of Cu in cellular respiration processes. Results further indicate that the size of the MNP does impact the rate of single cell lysis, which may be related to the redox kinetics at the cell/MNP interface.