Multiplex PCR: Meeting targets for rapid detection of Salmonella serovars
Salmonellosis is probably one of the most widely recognised types of foodborne disease (FBD) in the US. It is certainly the most frequently reported bacterial illness associated with food, with more than a million cases reported each year in the US.
For food safety, regulations now require frequent microbial testing throughout the food processing environment: producers need fast tools that deliver results without delaying product delivery, and regulatory bodies need accuracy for tracing outbreaks.
Most people associate salmonellosis with poultry and eggs. However, records show that contamination occurs in many foods, such as fresh produce, milk and dairy products, cake mix, and pork and other meats. The bacteria that cause the disease, from the genus Salmonella, hop readily from animal to food via water and hand contamination, so strict hygiene measures help keep the disease in check.
Other food regulation measures in place to prevent salmonellosis include routine monitoring for Salmonella in food products and processing environments. Furthermore, regulatory officials stay alert to outbreaks through public health surveillance and isolating microbes from clinical samples.
With any FBD, officials must find out what is causing the outbreak and where it comes from. Once they know these two things, they can apply control measures such as food recalls and identify breakdowns in the food safety chain. Traditionally, identifying the source of an outbreak involves microbial culture to show that a pathogen is present in a food item. With Salmonella, however, the situation is complicated.
Although the genus Salmonella contains only two species — S. enterica and S. bongori — there are around 2,500 serovars of the bacterium, each with unique features, behaviour, and origin. To track and trace the source of an outbreak, analysts must therefore identify the serovar involved — this traditionally involves isolation followed by culture using selective media. The current reference method, USDA-FSIS MLG 4.09, takes around three days to show presence of Salmonella. Analysts then need to identify each serovar immunologically using agglutinating anti-serum.
Two S. enterica serovars, S. ser. Enteritidis and S. ser. Typhimurium, are the serovars commonly associated with FBD in people, causing around half the total number of human cases. They are also among the top 10 serovars isolated from raw meat. Since regulatory officials now require frequent testing throughout food processing environments to protect the public from FBD, including salmonellosis, it is important that microbial testing protocols be rapid, specific, and highly accurate. Although there are rapid tests to identify Salmonella species in foods, there are few specific tests for the two most common serovars.
Culture-independent or molecular testing offers both accuracy and speed in modern food production environments. The Thermo Scientific SureTect Salmonella Species PCR Assay uses real-time PCR (polymerase chain reaction) to show microbial presence. The new Thermo Scientific RapidFinder Salmonella species, Typhimurium and Enteritidis Multiplex PCR Kit gives rapid, reliable detection and identification in poultry, pork and environmental samples in as little as 16 hours.
Validation studies show that the RapidFinder Salmonella Multiplex Assay gives sensitive and reliable results from food matrices and environmental samples, even in the presence of multiple Salmonella serovars. Results from experimental contamination in raw poultry and pork and environmental sponges showed better performance than the reference method. Using cultured isolates of highly similar serovars, the multiplex PCR kit performed better than commercial real-time PCR assays for inclusivity (100% versus 100% and 96%) and exclusivity (98% versus 92% and 97%).
Compared with three days for traditional culture-based testing, the RapidFinder Salmonella Multiplex Assay and other molecular methods can help protect food safety and extend product shelf life for public health and brand reputation. Find out more here.
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