DNA signatures speed detection of Salmonella.

Salmonella may soon be identified within hours, rather than in as long as a couple of weeks, thanks to a rapid-detection technique developed by Lawrence Livermore National Laboratory researchers. Investigators have identified several potential unique strands of DNA in a strain of S. enteritidis. Those pieces of DNA--signatures--were compared with the genomes from other strains of Salmonella closely related to S. enteritidis to ensure they were unique to the enteritidis strain.

The most common pathogen found in eggs, S. enteritidis, is estimated to be present in only about one in 10,000 or more eggs. This bacterium only becomes a problem when disease-carrying eggs have not been thoroughly cooked or are left unrefrigerated. It is difficult to distinguish this pathogenic Salmonella from all of the other Salmonella strains that do not cause disease. Neither chickens nor eggs with this bacterium show any symptoms of the disease.

Scientists at the University of California at Davis and at the California Animal Health and Food Safety Laboratory have been using the diagnostic DNA signatures. They validated the new DNA-based detection approach in a clinical setting, running the new tests in parallel with the classical, slower microbiological approach. It appears that the primers (DNA copies) are very specific and can speed testing. They're very useful in screening out negative samples.

In the classical approach to detecting S. enteritidis or other pathogens, a sample is incubated in a broth overnight. The sample is then grown in an agar plate for another night before suspicious colonies are selected for several days of more refined testing.

As a part of their work, the Livermore investigators designed copies of short unique DNA regions of S. enteritidis that could be used in the polymerase chain reaction (PCR). Once a sample is inserted into the PCR system, the primers seek out unique sequences of DNA, such as those from S. enteritidis. If present, the primers attach themselves to the DNA and make billions of copies, indicating a positive reaction. If not, the primers have nothing to which to attach themselves, indicating the absence of the pathogen.

With the laboratory's DNA signatures for S. enteritidis, it may be possible to eliminate or drastically reduce the level of these bacterial infections, researchers believe. It may also be possible to track the source of the bacterial infections, whether they stem from feed, water, a manure pile or even processing equipment. Researchers have filed for patent protection.

In May 2001, unique DNA signatures for plague discovered by researchers were used in northern Arizona to confirm the presence of a naturally occurring outbreak of plague within four hours. Normally, plague detection tests have required about seven to ten days.

Further information. Peter Agron, Lawrence Livermore National Laboratory, Biology and Biotechnology Research Program, 7000 E. Ave., L-441, Livermore, CA 94550; phone: [phone]; fax: [phone]; email: [e-mail].