To determine CFU/mL for each condition, a serial dilution (10-fold) in PBS was performed and spotted onto LB agar at least 3 times. LB agar plates were incubated for 24 h before colonies were counted. The log reduction factor (LRF) was determined by subtracting the average log 10 CFU/mL of the treatment condition (Zr-NT, 24 h; Zr-NT/Ag-Np/AgO, 24 h) from the average log 10 CFU/mL of the bacterial starting inoculum.