Protection against water- and air-borne bacteria as well as their detection at very low levels is a big challenge for the health care profession. The study’s main goal was to prepare bacterial filters with a tunable trapping effectivity. We revealed that the trapping efficiency of Escherichia coli estimated from the optical density of bacteria passed through the filter was exponentially dependent on the surface density of the polyacrylonitrile nanofibre membranes. This log/linear regression profile was proven for bacterial trapping efficiency higher than 99.9% which opens a door for easy and tunable constructions of ultrasensitive filters and/or nanosensors as well as for the standardization and quality control of nanofibre membranes.