Commutability of food microbiology proficiency testing samples.

AIM: Food microbiology proficiency testing (PT) is a useful tool to assess the analytical performances among laboratories. PT items should be close to routine samples to accurately evaluate the acceptability of the methods. However, most PT providers distribute exclusively artificial samples such as reference materials or irradiated foods. This raises the issue of the suitability of these samples because the equivalence-or 'commutability'-between results obtained on artificial vs. authentic food samples has not been demonstrated. In the clinical field, the use of noncommutable PT samples has led to erroneous evaluation of the performances when different analytical methods were used. This study aimed to provide a first assessment of the commutability of samples distributed in food microbiology PT. METHODS AND RESULTS: REQUASUD and IPH organized 13 food microbiology PTs including 10-28 participants. Three types of PT items were used: genuine food samples, sterile food samples and reference materials. The commutability of the artificial samples (reference material or sterile samples) was assessed by plotting the distribution of the results on natural and artificial PT samples. This comparison highlighted matrix-correlated issues when nonfood matrices, such as reference materials, were used. Artificially inoculated food samples, on the other hand, raised only isolated commutability issues. CONCLUSIONS: In the organization of a PT-scheme, authentic or artificially inoculated food samples are necessary to accurately evaluate the analytical performances. Reference materials, used as PT items because of their convenience, may present commutability issues leading to inaccurate penalizing conclusions for methods that would have provided accurate results on food samples. SIGNIFICANCE AND IMPACT OF THE STUDY: For the first time, the commutability of food microbiology PT samples was investigated. The nature of the samples provided by the organizer turned out to be an important factor because matrix effects can impact on the analytical results.

Detection and quantification of ATP and heavy metal with electronical micro-circuits.

In order to use whole eukaryotic cells as an active element in the detection and amplification of biological signals, for both in vitro and in vivo applications, we have undertaken a first approach to interface live cells and integrated circuit, and evaluate the possibility to develop a microbioreactor. An amplified photodiode system was designed and built as an electronical circuit in a way that it could easily be miniaturised. In parallel micro-chips with silicium chambers were used as microbioreactors to adhere cells. We showed here that this etched silicon chamber allows endothelial and CHO cells spreading, permitting determination of a number of cell properties {\it on line} providing appropriate integrated circuits are designed to perform the desired functions. The photodiode system reacting to the luminescent luciferase system permitted, through the use of appropriate software from a personal computer (PC) connected on line in vitro, the determination of ATP concentration, and using different luciferase transfected bacteria permitted the detection of constitutive or induced luminescence.