Horseradish peroxidase (HRP)-conjugated anti-E. coli IgG (ab20425; Abcam, Cambridge, UK) was diluted to 10 ng/mL in phosphate-buffered saline (PBS) containing 3% BSA and 0.05% Tween-20, and used as a labeling agent. PBS containing 3% BSA and 0.05% Tween-20 was used as a wash ...