New DNA test will improve tracking of Salmonella food-poisoning outbreaks

Recent data from the Centers for Disease Control and Prevention (CDC) indicate that food poisoning caused bySalmonellabacteria leads to 1.35 million infections, 26,500 hospitalizations, and 420 deaths in the United States per year. During an outbreak, the speed and simplicity of a test to detect specific types of bacteria are important for public health investigators to track down the source.

"Salmonellain a clinical or food sample may be present in very small amounts and thus requires very sensitive methods to detect them. Multiple cross-displacement amplification (MCDA) is a method that can detect very small amounts of DNA rapidly and is also performed at a single constant temperature, in contrast to the cycling of temperatures required in other methods such as PCR. This makes it a good fit for a simple, rapid, and sensitive bacterial detection test. Although an MCDA test for anySalmonellaalready exists, it does not distinguish between different serotypes," explained Professor Ruiting Lan, PhD, of the School of Biotechnology and Biomolecular Sciences at the University of New South Wales, Sydney, NSW, Australia.

The investigators developed an MCDA assay for each of the seven serovar (subtype)-specific targets ofSalmonella. All of these assays accurately detect as few as 10 copies of DNA and can produce results in approximately eight minutes. Importantly, these assays do not require specialized detection equipment, simplifying any future application in clinical or industrial settings. By combining these seven serovar-specific assays with the existing species assay,Salmonelladetection can be simplified and accelerated.

"The assays developed in this study are unique because the gene markers used were selected based on analyzing thousands of genomes. Thus, these markers future proofSalmonellaserotyping in the era of culture-independent diagnostic testing," commented Professor Lan.

Traditional methods to distinguishSalmonellaserotypes involve growing the bacteria from samples and then testing them to assign them to a serovar. The MCDA test is faster because it does not require first growing the bacteria in culture. Rather, it can detect very small amounts ofSalmonellaDNA.

Although there are hundreds ofSalmonellaserovars, the authors chose the five most commonly occurring in Australia, which cause more than 85 percent ofSalmonellainfections in that country. However, at least two of these serovars are also the topSalmonellaserovars throughout the world, therefore the researchers believe the results are applicable to other geographic regions.

Salmonellabacteria typically live in animal and human intestines and are shed through feces. Humans may become infected by ingesting contaminated water or food such as raw or undercooked meat, poultry, eggs, or egg products. Possible signs and symptoms ofSalmonellapoisoning include nausea, vomiting, abdominal cramps, diarrhea, fever, and headache.