Many current tests take days to complete and require samples to sent away to laboratories.

It could speed the closure of danger beaches - and their reopening once the danger has passed.

Millions of Britons are heading for the beach this summer, but hundreds of millions of gallons of raw or partially-treated sewage are discharged around the UK coastline every day.

These may harbour a variety of potentially harmful bugs.

Researchers from the Michigan School of Public Health have developed a portable testing kit.

It can yield a result in less than 45 minutes.

Magnetic field

The test works by a principle called "immunomagnetic separation".

This uses tiny beads coated with antibodies - which are designed to lock onto E.coli bacteria as they pass by.

The beads with bacteria attached can then be extracted with a magnet, and mixed into clean water.

A chemical process allows the bacteria to be broken open, to release a substance called adenosine triphosphate (ATP).

A marker chemical is then added which fluoresces when it meets ATP.

The amount of light, easily measured with a handheld luminometer, equals the concentration of E.coli bacteria.

The testing device costs about $5,000 to buy and each test approximately $5.