Researchers at the University of Melbourne in Australia have published a new study that could help foodborne disease outbreak investigators interpret the results of an important genetic typing test more accurately.
The Australian researchers looked at a test called multi-locus variable number tandem repeats variable analysis (MLVA), which is often used in the investigation of disease outbreaks. The test analyses specific DNA sequences on the bacterial genome (loci) that change over time sufficiently to distinguish outbreak strains from other strains of the same bacteria, but not so rapidly that connections between individual cases in an outbreak are lost.
The study examined the rates of change in MLVA profiles for a strain of Salmonella Typhimurium grown both in laboratory culture and in mice. Five loci are commonly used to type Salmonella Typhimurium by MLVA and it was discovered that three of these changed during the course of the study while the other two did not. The researchers therefore recommend that isolates with zero or one variation in the three rapidly changing loci, but no changes in the other two should be included in the same cluster during outbreak investigations.
The results were the same in laboratory culture and in mice, leading researcher Kathryn Holt to comment, “This tells us we don’t need to worry about where the bacteria were isolated from – humans or food.”
A report of the study is published ahead of print in the Journal of Bacteriology and an abstract can be found here.