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

Malaria transmission linked to mosquitoes' sexual biology

13 hours ago

Sexual biology may be the key to uncovering why Anopheles mosquitoes are unique in their ability to transmit malaria to humans, according to researchers at Harvard T. H. Chan School of Public Health and University of Per ...

Intermediary neuron acts as synaptic cloaking device

14 hours ago

Neuroscientists believe that the connectome, a map of each and every connection between the millions of neurons in the brain, will provide a blueprint that will allow them to link brain anatomy to brain function. ...

Skeleton of cells controls cell multiplication

14 hours ago

A research team from Instituto Gulbenkian de Ciencia (IGC; Portugal), led by Florence Janody, in collaboration with Nicolas Tapon from London Research Institute (LRI; UK), discovered that the cell's skeleton ...

New study shows safer methods for stem cell culturing

Feb 25, 2015

A new study led by researchers at The Scripps Research Institute (TSRI) and the University of California (UC), San Diego School of Medicine shows that certain stem cell culture methods are associated with increased DNA mutations. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.