How to Use Bacterial Enrichment to Accelerate Food Pathogen Detection

Simultaneous selective enrichment shares the benefits of using UPB in terms of cost savings, but it also reduces enrichment time when compared with standard protocols (see Table 1). Additionally, by reducing the number of analyses needed, simultaneous selective enrichment contributes to the ergonomic wellness of laboratory workers.

Optimizing Harmonized Enrichment

Several parameters might influence the effectiveness of bacterial enrichment. The number and variety of standard protocols clearly illustrates the complexity and the significance of this step. For example, chapter five of the Bacteriological Analytical Manual (BAM) prepared by FDA includes more than 20 procedures to detect Salmonella spp. in foodstuffs. This dearth of standardization is especially common in the context of simultaneous enrichment.

Two factors that affect the success of co-enrichment are the bacterial species and food matrix type being tested. First, scientists should adapt the buffering properties and the selectivity of their medium to the chemical characteristics of the food sample, such as fat content and pH, as well as the type and ratio of microbial flora. It would be difficult to design a co-enrichment protocol that suits the large variety of food types. For this reason, simultaneous enrichment should target a specific food category. Similarly, co-enrichment works best when performed on pathogenic bacteria with similar nutritional and temperature needs, as well as comparable susceptibility to inhibitory compounds.

Validated Protocols with Simultaneous Pathogen Detection

Over the last decade, scientists have developed innovative protocols that enable the simultaneous enrichment of several pathogen targets in a single bag. This development allows more flexibility in food microbiological routine labs and improves the overall ease of use of the pathogen detection workflow. In the context of food safety regulations, these innovative protocols must demonstrate an equivalent level of performance to related reference methods. Recently, we developed a new harmonized protocol that enables the simultaneous growth of Enterobacteriaceae, specifically Cronobacter spp. and Salmonella spp., thanks to the addition of a proprietary reagent to the buffered peptone water. The ISO 16140-2 validation demonstrated that enrichment using this protocol, followed by PCR or chromogenic agar detection for Cronobacter spp. and Salmonella spp., provides the same level of sensitivity, specificity, and selectivity as each individual reference method.

Harmonized enrichment of food samples allows the simultaneous pathogen detection of several targets. It reduces the cost of analysis and increases flexibility in the laboratory. To achieve an acceptable level of performance, however, this harmonized enrichment can be achieved only on microorganisms that share similar physiologic characteristics. Also, in the context of food safety regulations, these harmonized enrichments are useful when they allow the co-detection of several microorganisms of interest relevant for a single food matrix. The standardization of co-enrichment methods will hopefully lead to quicker and more accurate detection of pathogens in food and reduce the incidence of foodborne illness around the world.

Dievart is R&D Manager in the food science division at Bio-Rad Laboratories. She can be reached at [email protected]. Bichot is business unit marketing manager in the food science division at Bio-Rad Laboratories. Reach him at [email protected].