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Pathogen Detection Solution for Food Samples

Detection of pathogen in food using culture media, chromogenic culture media, immunology and molecular based method.

Pathogen Detection

Detecting pathogens is an important aspect of food safety, as it is aimed at detecting harmful microorganisms that could harm consumers. Pathogen detection requires both accuracy and timing – accurate and timely detection helps prevent contamination, and further ensures food quality and safety.

Various methods are used to detect pathogens in food, ranging from traditional culture media to advanced molecular-based techniques. They provide critical tools for meeting regulatory standards and safeguarding public health against pathogens such as Salmonella, Listeria monocytogenes, and Listeria spp.

Traditional Culture Media

The pre-enrichment (or primary enrichment) and selective enrichment (or secondary enrichment) processes up to more than 32 hours. Hence, safe and efficient culture media preparation is an important part of cell and microorganism sample growth in the lab. To help ensure that the quality control of culture media in a microbiology laboratory can be performed accurately and quickly, DKSH offers ready-to use culture medias for Salmonella and Listeria detection.

Example: Salmonella

Products for Salmonella detection according to EN-ISO 6579:2002

Buffered peptone water (pre-enrichment)
Rappaport Vassiliadis broth (selective enrichment)
XLD and other second agar: for example, Hektoen Enteric Agar, Brilliant Green Agar, modified, SS-Agar and chromogenic media like Salmonella Chromogen Agar or HiCrome Salmonella Agar, improved for detection

The procedure of Salmonella culture

Example: Listeria Monocytogenes and Listeria spp.

Products for Listeria detection according to EN ISO 11290-1:2017:

Primary enrichment in half-Fraser broth: incubation changed to 25 h ± 1 h.
Secondary enrichment in Fraser broth updated to 24 h ± 2 h.
Enriched half-Fraser and Fraser broths may be refrigerated before transfer or isolation on selective agar for max. 72 h.
Incubated isolation plates can be refrigerated for a maximum of two days before reading
Microscopic confirmation aspect is optional in the case of use of agar specific for pathogenic Listeria spp.
New performance characteristics included
CAMP and catalase tests are optional

The procedure of Listeria culture

Chromogenic
Culture Media

This technology is based on soluble colorless molecules called chromogens, composed of a substrate targeting a specific enzymatic activity and a chromophore. When the target organism’s enzyme cleaves the colorless chromogenic conjugate, the chromophore is released. In its unconjugated form, the chromophore exhibits its distinctive color and forms a precipitate due to reduced solubility

Immunology

Antibody-based detection tests

Antibody-based detection relies on a highly specific and sensitive antibody-based system for the antigen present on the target pathogen. Most antigens contain amino acid sequences that are distinguishable among the target pathogens and other related non-target organisms. This specificity allows strong reactivity of antibody to the antigen in the target pathogen.

Enzyme-linked immunosorbent assay (ELISA)

Enzyme-linked immunosorbent assay is one such standard pathogen detection tool, whose detection system is based on enzyme-labeled reagents.

Molecular Based Method

Scientists have developed nucleic acid-based methods for detection and identification of specific DNA or RNA sequence of the target pathogen. Detection of a target nucleic acid sequence is performed by simple polymerase chain reaction (PCR), hybridization probes, or primers. Nucleic-acid based methods detect specific genes in the target pathogens associated with seafood.

Real-time PCR combines the specificity of conventional PCR with the quantitative measurement of fluorescence for monitoring amplification of specific genes in the target pathogens. A number of qPCR schemes have been designed to detect target genes such as the cholera toxin gene (ctxA) of V. cholerae or the tdh/trh genes of V. parahaemolyticus in fish and crustacean samples. Detection of multiple target genes of different species, serotype, or subtypes can be done in a single reaction by multiplex assay.

Blenders, Diluters
and Filter Bags

Loop-mediated isothermal amplification (LAMP) is another variant of nucleic acid-based methods. Most LAMP-based assays have been used for detection of V. parahaemolyticus, V. vulnificus, Salmonella spp., and L. monocytogenes in seafood and environmental samples. LAMP is proven to be more specific and sensitive compared to the other PCR-based assays for the detection of foodborne pathogens.