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.

[Seasonal evolution of blood levels of thyroxine and triiodothyronine in the post-pubertal bull in France and Iraq. Concomitant variations of LH and testosterone]. / Evolution saisonnière des niveaux plasmatiques de thyroxine et de triiodothyronine chez le taureau post-pubère en France et en Irak. Variations concomitantes des taux de LH et de testostérone.

An inquiry was conducted in 2 performance testing stations, A and B located in France and Iraq, respectively. In both stations, at solstice and equinox, thirty 15 month-old Holstein bulls were blood sampled for plasma LH, testosterone, thyroxine and triiodothyronine determination. For LH, no coherent seasonal effect was found. As regards testosterone, maximal mean values were obtained in December in both stations (3.4 ng/ml). In A as well as in B, thyroxine peaked in December reaching 64.6 ng/ml and 77.8 ng/ml, respectively, and falling down to 49.4 ng/ml and 65.6 ng/ml, respectively in June. The difference was significant for A (P less than 0.001). For T3, the fall from December (1.42 ng/ml in A and 1.68 ng/ml in B) to June (1.09 ng/ml in A and 1.26 ng/ml in B) resulted in about the same relative value and was significant (P less than 0.005) in both stations. The detrimental effect of high temperatures on semen quality does not seem to be mediated by an alternation of thyroid function.

Knobbed spermatozoa in two Normande bulls.

Two unrelated yearling Normande bulls in a bull stud had 26 and 18% knobbed spermatozoa as well as other major sperm abnormalities. One of the bulls was eliminated from the bull stud because of poor semen quality and growth performance. The other bull was maintained for additional semen evaluation, during which time the mean percentage of major sperm abnormalities decreased, indicating amelioration of a transient testicular degeneration.