PROJECT SUMMARY Multidrug-resistant bacterial infection is becoming a health crisis worldwide. Treatments for previously “untreatable” bacterial infection have been the spotlights of antibacterial studies, including minimizing the emergence, spread and persistence of drug-resistance genes, as well as directly neutralizing virulence factors. Many of these bacterial pathogens possess retractile pili, which are either part of secretion systems required for gene/protein transfer, or responsible for virulence. In this project, it is proposed to manipulate pili through ssRNA phages as an anti-virulence strategy against pathogenic bacteria and/or dissemination of antibiotic resistance genes. From the preliminary data, the infection of ssRNA phage MS2 or Qβ was found to cause the detachment of E. coli conjugative F-pilus through single-cell studies using fluorescence microscopy. Aim 1 is to examine the F-pili detachment efficiency by varying different mutants of Type IV section systems and growth conditions, and investigate how to reach 100% detachment efficiency. In addition, the study will be expanded to other types of retractile pili and their ssRNA phage systems for pili detachment. Aim 2 is to identify the essential components of ssRNA phages for F-pilus detachment and design novel minimal systems or virus-like particles to efficiently detach the F-pilus.