Lab Test Simultaneously Detects Foodborne Pathogens

A laboratory test that simultaneously detects Salmonella and a deadly form of E. coli O157:H7 has been developed by Agricultural Research Service microbiologists in Ames, Iowa.

The new test uses a technique called fluorescent polymerase chain reaction (PCR) to detect the two foodborne pathogens. PCR makes many copies of genetic material called DNA, the basic genetic building blocks of bacteria and other living organisms. Then two fluorescent probes, which are present in the PCR tube, specifically detect Salmonella and O157:H7 by detecting the DNA specific to these bacteria.

So far, the test has been evaluated to detect between one and 10 bacterial cells in meats and feces that are cultured for 6 to 16 hours prior to performing PCR, which requires only 4 hours. This makes the new test several hours faster than standard culturing techniques now used to detect bacterial contamination in meat or livestock feces.

Detecting the deadly E. coli O157:H7 is critical to stopping the spread of this disease-causing bacterium, which causes bloody diarrhea and can be fatal. Salmonella and E. coli are found in animal feces and spread to humans through undercooked contaminated foods. Each year, about 40,000 reported cases of salmonellosis and 73,000 estimated cases of diarrheal illness due to O157:H7 occur in the U.S.

ARS microbiologists Vijay K. Sharma and Steve A. Carlson at ARS’ National Animal Disease Center in Ames validated the test by using artificially contaminated beef, chicken and cattle feces. The test would be just as accurate on pork.

The meat processing industry, which slaughters more than $50 billion worth of livestock annually, could use this technology to meet current federal regulations that mandate zero tolerance for visible fecal contamination and for E. coli O157:H7.

Sharma presented the findings today at the American Society for Microbiology (ASM) meeting in Los Angeles.

ARS is the chief research agency for the U.S. Department of Agriculture.

Scientific contact: Vijay K. Sharma, National Animal Disease Center, P.O. Box 70, Ames, IA 50010, phone (515) 663-7279, fax (515) 663-7458, vsharma@nadc.ars.usda.gov.