Food contaminated with microorganisms such as bacteria, yeasts, molds or viruses may pose a risk to the consumer. In addition to the detection of pathogenic microorganisms, it is important to monitor typical spoilage organisms in order to reduce losses during production.
Microorganisms are creatures of microscopically small size, mainly organized as single-cell organisms, while some of them may occur multicellularly. They can be found everywhere in the natural environment (water, soil, air, etc.). Microorganisms may naturally be present in foods or on the surfaces of foods (e.g. fresh vegetables) or added as contamination during the manufacturing process of food products (e.g. insufficient hygiene in meat processing).
In food industry, it can be distinguished between different categories of microbiological contamination:
Pathogenic microorganisms are either not allowed at all to occur in the foodstuff or they are limited to a specified number of cells per gram food. These limits differ to the respective food matrix. (For more information please visit the DGHM Website.) If limits are exceeded, this might have tremendous consequences for consumer’s health. Therefore, a zero tolerance per 25 g of food sample is predicted for most of all common pathogens (Salmonella, Campylobacter, E. coli, etc.).
In general, you can differentiate between two methods of microbiological testing: food testing and hygiene monitoring / cleaning control.
Microbiological tests for cleaning and hygiene control detect general residues of foods on insufficient cleaned surfaces in the production environment. These residues of nutrients are the basis for growth of microorganisms.
Colony counting in foods or on surfaces can be done using the ready-to-use Compact Dry plates. Compact Dry plates are available for 13 different parameters of analysis. General method base of examinations with Compact Dry is the cultivation of microorganisms on standard nutrient media. The test principle is based on specific chromogenic substrates which are converted into colored products by the metabolism of microorganisms. Beside examination of diluted food samples, Compact Dry is also suited for swab samples from surfaces or incubation of membrane filter samples from liquids.
Residues of foods on surfaces can be detected using protein tests (RIDA®CHECK) or ATP measurements (LuciPac™Pen). Determination of proteins roughly describes the stage of contamination by color change of the colorimetric detection reagent. However, the relative amount of ATP (Adenosintriphosphat) or AMP (Adenosinmonophosphat) respectively can be measured very precisely. A special bioluminescence reaction which requires the presence of ATP or AMP is recorded in a special luminometer instrument (Lumitester™ PD-20). Both systems are suited for consistent control of efficiency of cleaning procedures. These controls ensure maintenance of general industrial hygiene. Surfaces which are hygienically clean can reduce the risk of product contaminations.
| Compact Dry | RIDA®STAMP | RIDA®CHECK | Lumitester™ PD-30 |
|---|---|---|---|
| Ready-to-use nutrient plates | Ready-to-use agar plates | Protein test | ATP / AMP measurement |
| Microbial count on surfaces and in diluted food samples | Microbial count on flat surfaces in the production environment and on solid foods | Swab test for the detection of food residues on surfaces | Detection of food residues on surfaces |
| Easy and safe | Easy to use and to evaluate | Rapid and reliable method | Rapid and convenient using LuciPac®Pen with integrated swab |
Toxic residues of bacteria in food and beverage samples can be analyzed with test kits for bacterial toxins. Common test formats for microbial food testing are ELISA assays, real-time PCR tests, nutrient plates and agar plates.
For detection of pathogenic bacteria, immunological based methods (ELISA) are available. RIDASCREEN® assays are based on the sandwich technology, in which the antigen (bacterial surface protein) will be captured in the well of a microplate and detected by adding a second antibody which is marked with a special detection enzyme. The immunological detection requires suitable pre-enrichment procedures depending on the kind of pathogen bacteria.
The detection of bacterial toxins is possible directly from food samples (RIDASCREEN® SET Total and RIDASCREEN® SET A,B,C,D,E) or is used for indirect detection of toxin producing pathogenic bacteria subsequent to appropriate pre-enrichment.
The identification of pathogenic bacteria and viruses can be performed with molecular biological systems, e.g. the highly specific real-time PCR kits of the SureFast® PATHOGEN line. The modular system consists of optimized DNA preparation via spin filter columns and the commonly used TaqMan hydrolysis probe technology linked with FAM dyes for detection. It can be performed with all commonly available types of real-time PCR thermo cyclers. The internal amplification control is integrated into all PLUS kits. The appropriate choice of amplification control dye depends on the cycler type where the reaction will be applied to.
| RIDASCREEN® | SureFast® | Compact Dry | RIDA®STAMP |
|---|---|---|---|
| Immunological test (ELISA) | Molecular-biological test (real-time PCR) | Ready-to-use nutrient plates | Ready-to-use agar plates |
| For the detection of bacteria and bacterial toxins | For the detection of bacteria and viruses | Microbial count on surfaces and in diluted food samples | Microbial count on flat surfaces and on solid foods |
| Rapid and reliable method | Highly specific and fast; suitable for all standard PCR thermal cyclers | Easy and safe | Easy to use and to evaluate |
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Usage of Compact Dry AQ is a simple and safe test procedure for determination and quantification of heterotrophic water bacteria from water samples (drinking and ultrapure water). The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry CF is a simple and safe test procedure for determination and quantification of coliform bacteria in foods, cosmetics or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry EC is a simple and safe test procedure for determination and quantification of coliform bacteria and E. coli in foods, cosmetics, water or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry ETB is a simple and safe test procedure for determination and quantification of Enterobacteria in foods, cosmetics or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry ETC is a simple and safe test procedure for determination and quantification of Enterococcus in foods and water samples. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry LM is a simple and safe test procedure for detection of Listeria monocytogenes in pre-enriched samples of foods. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry LS is a simple and safe test procedure for quantification of Listeria contaminations in foods or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Compact Dry PA is a simple and safe test procedure for the determination and quantification of Pseudomonas aeruginosa counts in foods, cosmetics, water samples or pharmaceutical materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry SL is a simple and safe test procedure for detection of Salmonella in pre-enriched samples of foods or raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry TC is a simple and safe test procedure for determination and quantification of aerobic mesophilic count in foods, cosmetics or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry VP is a simple and safe test procedure for detection and quantification of Vibrio parahaemolyticus as well as Vibrio spp. in foods or raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry BC is a simple and safe test procedure for determination and quantification of Bacillus cereus in foods or raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry X-SA is a simple and safe test procedure for determination and quantification of Staphylococcus aureus in foods, cosmetics or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry YM is a simple and safe test procedure for determination and quantification of yeasts and molds in foods or raw materials – as well as pharmaceutical raw materials. The ready-to-use plates consist of a special 50 mm diameter petri dish containing a detection specific nutrient pad.
Usage of Compact Dry YMR (rapid) is a simple, safe and fast test procedure for determination and quantification of yeasts and molds in foods or raw materials – as well as pharmaceutical raw materials
Sampling device consisting of sterile swab in 10 ml sterile PBS buffer for quantitative detection of microorganisms in environmental samples in combination with Compact Dry medium systems.