Direction methods - Detection metods
22 important questions on Direction methods - Detection metods
Why do you sample foods?
- aerobic plate count, entrobacteriaceae, pseudomonas, lactobacilli, sporeformers, yeast, mould.
- For this you do a storage test (you check if the product can still be used at the due date).
To check food safety: pathogens
- Salmonell, Campylobacter, Listeria monocytogenes, Clostridium Perfringens.
- For this you perform a challange test (See if a pathogen can grow or not, if they can not grow you can have a 2 log in your product).
What plate do you use for food quality and what information does it give you?
- all products
Indicator for:
- quality of product
- quality of ingredients
- storage problems
- poor hygiene
When is a product spoilt?
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Which micro-organism is a indicator of quality for heated products?
This is because they are suppose to be destroyed with heating.
So if they are present it is an indicator for:
- Inadequate heating
- contamination
- poor hygiene
Which micro-organism is a indicator for quality for fruits, vegetables and (MAP) meat?
indicator for:
- quality of product
- storage problems
- poor hygiene
What is the main micro organism spoiling meat (NOMAP)?
What are the different methods for detection?
- traditional culture techniques (plating on selective or non selective media)
- TEMPO
- Chromogenic media
- Immunological methods (VIDAS, dynabeads)
- Molecular techniques: PCR, DNA detection, RFLP, microarray, RNA-sequencing
- DNA/RNA technology
What is the tempo method?
- You have a dilutiong of which you pipet different volumes in the wells.
- There are dyes added that only bind to for instance entros or to every cel for TVC.
- The chance that a cell is present becomes smaller sins the volume becomes smaller.
- If one cell is present it will start growing and there will be UV light reflected
- Because of this you can make an estimation.
How do you aprove a new method?
What are the pros and contras of the TEMPO method?
+ no confirmation step for enteros
+ results available one day sooner
- estimation of counts
- no access to raw data
When do you choose a 3 class and when do you choose a 2 class sampling plan?
(salmonella, E.coli)
3-class: for things that need to grow in order to be toxic.
(B. cerus, C. perfringens, S. aureus, V. parahaemolyticus)
What would be the ideal sampling method?
- Flexibility (multi-target, detection and identification, non-destructive)
- Sensitivity: 100%
- Specificity: 100%
- Easy-to-use: fully automated
- Speed: fast, on-line
- Costs: low
What is a sensitivity?
this is about a safety issue
What are chromogenic media for ditection of pathogens?
What is the principle of immunological methods?
the antigen is the microorganism or toxic an can react specifically with the antibody.
What is a latex agglutination test?
What is the ELISA method?
Sandwich model.
Een antibody is attached to a surface, a antigen (micro organism) is added an they will bind. Then a second antibody ad added an this wil bind to the other side of the antigen. Then a substrate will bind and you wil have a sandwich formulation able to convert light so it will give a colour.
What is a VIDAS?
- Antibody coated tip
- Salmonella antigen is bound
- The immuno complex is detected by anti-Salmonella antibody, conjugated to an enzyme
- The bound enzyme catalyses the added substrate
- The product is released in the test strip and fluorescence is measured by the VIDAS scanner
What is immuno-magnetic concentration?
Magnetic beads with an antibody are added. The pathogens attach and stick to the side.
What is ricombination phage protein technology?
What is a microarray?
Sample is added. If salmonela is present the salmonella gene will be multiplied and you will get a positive signal in this part.
So multiple organisms can be found.
Which three methods can be used for enumeration of bacteria in products?- Spiral plater
- PCR
- ELISA
- Chromogenic media
- TEMPO
Spiral plate
Chromogenic media
TEMPO
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