When it comes to rapid methods, antigen/antibody-based assays such as ELISA or lateral flow have been in use for many years, but a growing concern with these methods is the cross-reactivity with non-target organisms. DNA-based methods are generally considered to be more accurate, as they target a specific and unique DNA sequence of the bacteria.
Among the several kinds of DNA-based rapid methods, polymerase chain reaction (PCR) has been widely used for foodborne pathogen detection, and there are multiple vendors offering validated PCR methods to detect Salmonella, STEC (O157 and non-O157), Listeria spp., L. monocytogenes, Cronobacter, and other organisms. PCR uses Taq polymerase and repeated cycling (heating and cooling) to amplify DNA, relying on instrumentation capable of rapidly heating and cooling. In addition, PCR methods typically require multiple steps for processing enriched food samples and amplify target DNA for detection of pathogens.
Newer DNA-based methods such as the LAMP (loop mediated isothermal amplification) technology that 3M commercialized offer an alternative to PCR (see Table 2). These tests are also globally validated for their ability to detect the Salmonella, E. coli O157, Cronobacter, and other key pathogens implicated in LMFs, but with fewer steps and simpler instrumentation. LAMP uses Bst polymerase that has strand displacement activity, allowing amplification at a single temperature without the need for cycling through series of temperatures. In addition, Bst polymerase has been shown to be more resistant to inhibitors from media or food matrices that may compromise PCR results. The 3M Molecular Detection System based on LAMP integrates a proprietary bioluminescence solution for detection that offers a sample preparation process with only two transfer steps and no need for DNA extraction and purification steps.
The PCR and LAMP assays have been validated for various LMFs. Manufacturers need to select an appropriate method to fit their purpose and need based on comparative benefits such as cost, ease of use, and validations.
Lastly, whole genome sequencing (WGS) provides the complete DNA makeup of a test subject, allowing organisms to be differentiated with precision not possible with other technologies. WGS is an emerging technology for food safety applications, but it is mainly being used by regulatory agencies such as FDA and USDA to pinpoint sources of contamination during outbreaks. Its wide use for routine food safety testing is debatable given the cost and complexity of the method.
LMF, High Economic Pressure Businesses
The LMF industry is focusing on major changes to produce the highest food quality. New requirements are being enacted in supply chain controls, environmental monitoring programs, training, and recordkeeping. Greater enforcement of food safety laws and regulations is pushing LMF manufacturers to place safety at the forefront.
LMF processors are forced to balance countless procedural, competitive, and economic pressures alongside needs to cut testing time and release products to market faster. But as recent outbreaks and recalls attest, it’s imperative that they not take their eye off the ball when it comes to food safety. With goals of mitigating risk at every step and improving operational efficiencies and productivity, thoughtful workflows—from expertly designed, validated, and verified cleaning regimens to more automated pathogen testing practices to safe storage approaches—can help LMF products safely and sufficiently reach consumers.
Dr. Rajagopal is a senior global technical service specialist with 3M Food Safety. Reach him at firstname.lastname@example.org.
The “Control of Salmonella and Other Bacterial Pathogens in Low-Moisture Foods” book reviews the current state of the science on the prevalence and persistence of bacterial pathogens in low-moisture foods and describes proven techniques for preventing food contamination for manufacturers who produce those foods. Go to www.Wiley.com and type in book title to learn more.—FQ&S