Silver Ions Inhibit Bacterial Movement and Stall Flagellar Motor

Silver (Ag) in different forms has been gaining broad attention due to its antimicrobial activities and the increasing resistance of bacteria to commonly prescribed antibiotics. However, various aspects of the antimicrobial mechanism of Ag have not been understood, including how Ag affects bacterial motility, a factor intimately related to bacterial virulence. Here, we report our study on how Ag+ ions affect the motility of E. coli bacteria using swimming, tethering, and rotation assays. We observed that the bacteria slowed down dramatically by >70% when subjected to Ag+ ions, providing direct evidence that Ag+ ions inhibit the motility of bacteria. In addition, through tethering and rotation assays, we monitored the rotation of flagellar motors and observed that the tumbling/pausing frequency of bacteria increased significantly by 77% in the presence of Ag+ ions. Furthermore, we analyzed the results from the tethering assay using the hidden Markov model (HMM) and found that Ag+ ions decreased bacterial tumbling/pausing-to-running transition rate significantly by 75%. The results suggest that the rotation of bacterial flagellar motors was stalled by Ag+ ions. This work provided a new quantitative understanding of the mechanism of Ag-based antimicrobial agents in bacterial motility.

Automated summary

Silver (Ag) in different forms has gained attention for its antimicrobial activities, especially as bacteria become more resistant to antibiotics. However, the mechanism of how Ag affects bacterial motility is not fully understood. In this study, we found that Ag+ ions significantly inhibited the motility of E. coli bacteria and increased the tumbling/pausing frequency. Using the hidden Markov model (HMM), we analyzed the results and found that Ag+ ions decreased the bacterial tumbling/pausing-to-running transition rate. This work provides new quantitative understanding of Ag-based antimicrobial agents in bacterial motility.