[NEW DELHI] A test that detects tiny amounts of Salmonella bacteria in drinking water has been developed by Indian scientists.
Salmonella bacteria, which can cause typhoid fever and gastroenteritis, are a major public health hazard in many developing countries. More than two million people catch typhoid each year — 90 per cent in Asia.
It takes just 15 bacteria to cause illness and people reliant on natural water resources — which can contain bacteria from untreated sewage — are particularly vulnerable to infection.
Conventional detection techniques take five days to give a confirmed result because the bacteria must be cultured before they can be identified and the tests cannot detect salmonella if there are fewer than 102 bacteria present.
The new method provides results in three hours and can detect as few as ten bacteria. It was developed by scientists from the Indian Institute of Toxicology Research (IITR) and Jamia Hamdard University, and published in Science of the Total Environment last week (15 February).
Public health officials need good data about the locations that are at risk of Salmonella infection so they can plan vaccination and other prevention strategies.
The researchers took water samples from rivers in northern India. They chose a section of DNA specific to a wide range of Salmonella bacteria and detected whether it was present in the water using a technique called polymerase chain reaction, which amplifies any DNA that matches the target section.
Matching strands of DNA attached to a florescent tag were then added to the samples. When these bind to the complementary target sections, a fluorescent signal is produced — indicating the presence of Salmonella.
The test works within three hours and is highly sensitive — it can detect Salmonella in water heavily contaminated by other bacteria such as Escherichia coli, say the researchers.
"The test is exciting because it does not require a culture, a process that is slow and relatively insensitive, and is reasonably fast — although it is by no means a rapid test," said W. Abdullah Brooks, head of the infectious diseases unit at the International Centre for Diarrhoeal Disease Research, Bangladesh.
"[It] potentially gives scientists, regulators, industry and others a reasonably fast, sensitive and specific tool for monitoring the level of contamination of surface water, as well as tracking the most heavily polluted locations for intervention," Brooks told SciDev.Net.
He added that the test would enable public health officials to make timely recommendations to the public about water treatment.
Science of the Total Environment doi 10.1016/j.scitotenv.2009.11.056 (2010)