杏吧原创

BEACH-GOERS around the world may be having their swimming fun spoilt for no
reason by a harmless bug.

A bacterium that was thought to be a sign of sewage has now been found to
thrive naturally in the wet sands that border temperate rivers and lakes. It
could mean that freshwater swimming beaches are being closed down even when
there is no sewage contamination.

E. coli is a common bacterium found in the intestines of birds and
mammals. Some strains can cause food poisoning, but most are harmless. Because
E. coli occurs in faeces鈥攚hich are laden with other
disease-causing bacteria and viruses鈥攊t is often used as an indicator for
sewage pollution.

Richard Whitman of the US Geological Survey spent 10 years studying the
shores of the Great Lakes, where beaches are sometimes closed due to high levels
of E. coli. He has found that concentrations of the bacterium often
exceed 10,000 bugs per 100 millilitres of sand鈥攅nough when mixed with
beach water to exceed the maximum safety level set by the Environmental
Protection Agency.

But genetic tests showed that less than half of the sand bugs came from
seagull faeces or the lake water. Whitman says this strongly suggests that the
bugs occur naturally on the beaches. He found that some bacteria even persist
during the winter when the beaches are covered in snow and ice. 鈥淭he bacteria
are living there,鈥� agrees Roger Fujioka, a microbiologist at the University of
Hawaii.

Whitman claims this is the first time they have been shown to persist in
beach sand. Any freshwater sandy shore could have high levels of E. coli, he
says, and using the bug as an indicator for water quality may be flawed.