Sharpening a test for tracing food-borne illness to source

Jun 23, 2014

Research from the University of Melbourne, Australia, could make it easier for public health investigators to determine if a case of food poisoning is an isolated incident or part of a larger outbreak. The findings are published ahead of print in the Journal of Bacteriology.

The study focuses on a test called multi-locus variable number tandem repeats variable analysis (MLVA). The test, which is increasingly used in the detection and investigation of foodborne outbreaks, analyzes specific sequences of DNA (called loci) that change rapidly enough over time to distinguish strains from other circulating strains of the bacteria but not so rapidly that connections could be masked by changes arising during the course of an outbreak.

However, the rates at which MLVA profiles change have not been directly investigated for Salmonella, and thus it is sometimes unclear how these profiles should be interpreted in the context of outbreak detection and investigation.

In the study, the investigators grew an isolate of Salmonella Typhimurium from an Australian outbreak, and observed changes in its MLVA profile during more than 28,000 generations of growth in the laboratory. Then, using the same bacterial lineage, they observed changes in MLVA profile during 500 days of growth in mice.

They estimated the rates of copy number change at each of the five loci that are commonly used for S. Typhimurium MLVA. Three of the loci saw changes in the DNA, but two did not. Based on these results, the researchers are recommending that isolates with zero or one variation in the three rapidly changing loci but no differences in the other two should be considered part of the same cluster.

They also noted that the relative rates of change among the loci were the same in the Petri dish studies and in the mouse study.

"This tells us we don't need to worry about where the bacteria were isolated from—humans or food," says Kathryn Holt, an author on the study.

MLVA is used for investigations of food-borne illnesses besides Salmonella, including Listeria, and E. coli. It is the primary method for investigations of Salmonella outbreaks in Europe, the UK, Australia, and elsewhere, says Holt.

"In the U.S., the Centers for Disease Control and Prevention uses another technique called PFGE for initial investigations and follows that with MLVA," she says.

Explore further: Food safety specialist says food poisoning cases underreported

add to favorites email to friend print save as pdf

Related Stories

Historically low number of Danes infected with salmonella

Jun 20, 2014

The number of Danes who contracted a salmonella infection reached a historic low level in 2013. More than half of those infected became ill during a trip abroad. For the third year in a row no salmonella cases were linked ...

Do people and pigs share salmonella strains?

Apr 03, 2014

If antimicrobial-resistant Salmonella is showing up in pigs, then are bacon-loving people also at risk? In his latest research, NC State population health and pathobiology professor Sid Thakur looks at serotypes, ...

Recommended for you

Molecular gate that could keep cancer cells locked up

Jul 31, 2014

In a study published today in Genes & Development, Dr Christian Speck from the MRC Clinical Sciences Centre's DNA Replication group, in collaboration with Brookhaven National Laboratory (BNL), New York, ...

The 'memory' of starvation is in your genes

Jul 31, 2014

During the winter of 1944, the Nazis blocked food supplies to the western Netherlands, creating a period of widespread famine and devastation. The impact of starvation on expectant mothers produced one of the first known ...

Sugar mimics guide stem cells toward neural fate

Jul 30, 2014

Embryonic stem cells can develop into a multitude of cells types. Researchers would like to understand how to channel that development into the specific types of mature cells that make up the organs and other structures of ...

User comments : 0