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Eurofins Food testing Belgium

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Abstract bachelorproef 2016-2017Validatie van Rapid 'Salmonella binnen Eurofins Food Testing Belgium

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Abstract bachelorproef 2015-2016Measurement uncertainty tests for different parameters in microbiology food testing / Method validation of Pseudomonas CN agar and Rapid Pseudomonas aeruginosa agar for quantitative analysis of Pseudomonas aeruginosa in water samples

This bachelor’s thesis has two subjects: measurement uncertainty tests for different parameters in microbiology food testing and the method validation of Pseudomonas cetrimide naladixic acid (PCN) agar and Rapid Pseudomonas aeruginosa (RPSA) agar for quantitative analysis of Pseudomonas aeruginosa in water samples.

The measurement uncertainty is one of four validation parameters for a microbiological quantitative method validation. It is a parameter that quantifies the dispersion of results. These results are results of analyses in double with several quantitative methods, used in Eurofins Food Testing Belgium. The dispersion of these results is caused by varying the in double analyses on the basis of black box parameters. These black box parameters include a different analyst, different sampling, different matrices and others.  For the measurement uncertainty tests, four matrix categories must be tested. Category 1 are liquids and powders, category 2 are mixed solid food samples, category 3 are small solid food samples and category 4 are other solid food samples. The target is to test 10 samples for each matrix category for each quantitative method.

For the measurement uncertainty tests, previously analysed samples are used. These samples are naturally contaminated, which cause that these samples contain realistic concentrations of microorganisms. Each of these samples are registered in double and analysed in with other food samples in the flow of the routine.

A lot of widely tested methods in Eurofins Food Testing Belgium mostly achieved the target of ten samples for each matrix category. For a lot of less tested methods, the target isn’t achieved. There are various reasons. First, category 1 products aren’t widely tested in Eurofins Food Testing Belgium. Second, for some parameters food companies take precautions to avoid these micro-organisms in their products (ex. Listeria monocytogenes). Third, a lot of parameters (like anaerobic parameters or coliforms) experience difficulties to survive in the storing conditions (-20°C and aerobically).

Pseudomonas cetrimide naladixic acid (PCN) agar and Rapid Pseudomonas aeruginosa (RPSA) are both growth media for Pseudomonas aeruginosa. Pseudomonas aeruginosa is quantitative analysed by a membrane filtration. For this analysis method two media can be used. PCN agar is routinely used in Eurofins Food Testing Belgium for the quantitative analysis of Pseudomonas aeruginosa in water samples. This medium has a major drawback. The confirmation tests are complex and intensive. As an alternative, RPSA agar can be used. This medium needs no confirmation. In the method validation, both methods must be compared, to decide if RPSA agar can be used as an alternative for PCN agar.

A method validation for a quantitative method has four validation parameters: trueness, repeatability, reproducibility and measurement uncertainty. Both media are compared based on these four parameters.

Two separate validations were performed. For trueness, no data was acquired. In the first validation, samples of drinking water, groundwater and surface water were spiked with Pseudomonas aeruginosa. The samples were tested on both media and evaluated on the parameter repeatability. Both media have comparable results, but the variability is high, because there is a low colony count on the plates.

In the second validation, samples of drinking water and water in bottles for consummation were spiked with a higher concentration of Pseudomonas aeruginosa and were evaluated on repeatability, reproducibility and measurement uncertainty for both media. The results for both media were comparable and have a low variability.

Based on the results of both validations can be concluded that RPSA agar is a possible alternative to PCN agar.


Samenvatting eindwerk 1 2013-2014: Implementation - Validation of the method 'TEMPO-AC' for the determination of total aerobic mesophilic bacteria count and compare general methods in the context of automatisation in a routine microbiological laboratory
This bachelor thesis is about the TEMPO, an automated alternative test method in microbiological research. Also the use of petrifilms will be discussed. The bachelor thesis will be divided into four parts.
First of all, there will be a research to replace the Total Viable Count (TVC) kit with the Aerobic Count (AC) kit. The TVC is the method that is now used to determine total germ number. The producer of the TEMPO TVC has developed an improved method (the TEMPO AC). The old method is no longer supported by the manufacturer; therefore it is replaced by the TEMPO AC. There will be drawn a validation for this replacement. This includes the accuracy, repeatability, reproducibility and measurement uncertainty.
In the second part there will be more tests that can be performed on the TEMPO (Table 1). The lab currently uses the Total Viable Count (TVC), Escherichia coli (EC), Enterobacteriaceae (E) and total coliforms (TC) kits on the TEMPO. These tests are already accredited. In the study, coagulase- positive staphyloccoci (STA) and Lactic Acid Bacteria (LAB) kits will be added. There will be examined what impact this would have, practically, in the lab. These two kits will be further investigated. According to the guidelines of the TEMPO they must incubate at 30°C.  There will be examined whether the samples from the TEMPO could also incubate at 22°C.
For Staphylococcus aureus, the third test, there are also molded plates; the Brilliance Staph 24 agar plates. The correctness of these plates against the reference method (=ISO method) and the time savings for the laboratory will be examined.
Finally, the petrifilms will be tested. The petrifilms for yeasts and molds and total germ number will be examinated in the laboratory. The test will examine the difference between the petrifilms, the TEMPO and the ISO method.


Lieven Bauwensstraat 4
8200 Brugge
+32 (0) 50 31 02 52


Traineeship supervisor
Elke Peeters
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