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Biomedical subjects

C Lacroix

Publications and source records attributed to C Lacroix.

192 records · Page 11Linked to original sources
PubMedDate not supplied

Total DNA synthesis and cloning in Escherichia coli of a gene coding for the human growth hormone releasing factor.

A DNA containing a sequence coding for the human growth hormone releasing factor (hGRF) has been obtained by enzymatic assembly of chemically synthesized DNA fragments. The synthetic gene consists of a 140 base-pair fragment containing initiation and termination signals for translation and appropriate protruding ends for cloning into a newly constructed plasmid vector (pULB1219). Eleven oligodeoxyribonucleotides, from 14 to 31 bases in length, sharing pairwise stretches of complementary regions of at least 13 bases were prepared by phosphotriester solid-phase synthesis. The DNA sequence was designed to take into account the optimal use of E. coli codons. Oligomers were annealed in one step and assembled by ligation. The DNA fragment of the expected size (140 bp) was recovered and cloned into the pULB1219 vector. The expected sequence was confirmed by DNA sequencing.

Amino Acid Sequence↗
PubMedDate not supplied

Effect of chelatants on gellan gel rheological properties and setting temperature for immobilization of living bifidobacteria.

The effect of various concentrations of sequestrants (sodium citrate, sodium metaphosphate, and EDTA) was studied on gellan gel (1.5-2.5% (w/v)) setting temperature and rheological properties. Addition of EDTA between 0 and 0.8% (w/v) led to a progressive decrease of setting temperature. Citrate and metaphosphate decreased this parameter when added up to 0.4 or 0.6%, depending on gellan gum concentration, eventually resulting in the absence of gel formation at room temperature for the 1.5% gellan solution containing 0.4% citrate. This effect was accompanied by a significant decrease of gel strength and stiffness and might be attributed to the binding of the divalent cations required for chain association during gelation by chelatants. With the aim of lowering the gel setting temperature during the cell entrapment process while maintaining high mechanical properties, a gel made of 2.5% gellan gum and 0.2% sodium citrate was used to entrap Bifidobacterium longum ATCC 15707. Ions and pH of the inoculum during the immobilization step influenced the long-term mechanical stability of the gel beads during continuous fermentation in a stirred tank reactor. High stability as well as high biocatalyst activity was obtained when a washed cell suspension was used as the inoculum. Gellan gel produced by dissolving gellan gum in a sodium citrate solution may be a promising entrapment matrix for temperature-sensitive cells such as mesophilic lactic acid bacteria and eukaryotic cells.

Bifidobacterium↗
PubMedDate not supplied

Effect of inoculum composition and low KCl supplementation on the biological and rheological stability of an immobilized-cell system for mixed mesophilic lactic starter production.

Two strains of Lactococcus lactis subsp. lactis (L. lactis KB and KBP) and one of L. lactis subsp. lactis biovar. diacetylactis (L. diacetylactis MD) were immobilized separately in kappa-carrageenan-locust bean gum gel beads. Continuous fermentations were carried out in supplemented whey permeate in a 1-L pH-controlled stirred tank reactor inoculated with a 30% (v/v) bead inoculum and a bead ratio of 55:30:15 for KB, KBP, and MD, respectively. The process demonstrated a high productivity and microbial stability during the 7-week continuous culture. Compared with previous experiments carried out with an inoculum bead ratio of 33:33:33 for KB, KBP, and MD beads, respectively, the modification of the inoculum bead ratio had apparently little effect on free and immobilized, total and specific populations. A dominant behavior of L. diacetylactis MD over the other strains of the mixed culture was observed both with free-cell populations in the effluent and with immobilized-cell populations. Additional experiments were carried out with other strain combinations for continuous inoculation-prefermentation of milk. The data also confirmed the dominance of L. diacetylactis during long-term continuous immobilized-cell fermentations. This dominance may be tentatively explained by the local competition involved in the development of the bead cross-contamination and in citrate utilization by L. diacetylactis strains. The gel beads demonstrated a high rheological stability during the 7-week continuous fermentation even at low KCl supplementation of the broth medium (25 mM KCl).

Animals↗
PubMedDate not supplied

Continuous production of mixed lactic starters containing probiotics using immobilized cell technology.

The production of a mixed lactic culture containing Lactococcus lactis subsp. lactis biovar. diacetylactis MD and Bifidobacterium longum ATCC 15707 was studied during a 17-day continuous immobilized-cell culture at different temperatures between 32 and 37 degrees C. The two-stage fermentation system was composed of a first reactor (R1) containing cells of the two strains separately immobilized in kappa-carrageenan/locust bean gum gel beads and a second reactor (R2) operated with free cells released from the first reactor. The system allowed continuous production of a concentrated mixed culture with a strain ratio whose composition depended on temperature and fermentation time. A stable mixed culture (with a 22:1 ratio of L. diacetylactis and B. longum) was produced at 35 degrees C in the effluent of R2, whereas the mixed culture was rapidly unbalanced in favor of B. longum at a higher temperature (37 degrees C) or L. diacetylactis at a lower temperature (32 degrees C). Strain redistribution in beads originally immobilizing pure cultures of L. diacetylactis or B. longum was observed. At the end of culture, the strain ratio (7:1 L. diacetylactis/B. longum) in bulk bead samples was similar to that of individual beads. The determination of the spatial distribution of the two strains in gel beads by immunofluorescence and confocal laser-scanning microscopy showed that bead cross-contamination was limited to a 100 microm peripheral layer. Data from this study validate a previous model for population dynamics and cell release in gel beads during mixed immobilized-cell cultures.

Bacterial Adhesion↗
PubMedDate not supplied

Variations of moisture measurements in cheese.

Data were accumulated during interlaboratory trials for cheese moisture determination from laboratories using officially recognized methods: AOAC; International Dairy Federation, and Standard Methods for the Examination of Dairy Products (SM). In one trial, ranges of means of 5 cheeses were 0.67, 0.56, and 0.19% for 5, 9, and 8 laboratories, respectively. The lower ranges for the SM method were typical of 3 other interlaboratory trials, with ranges of 0.27, 0.34, and 0.34% for 6, 7, and 5 laboratories, respectively. Within one laboratory, there were no significant differences among the 3 methods, but they all gave about 0.2% lower results than 2 other methods, one using freeze-drying, followed by drying in a vacuum, the other using cheese that was spread on sand and dried in a vacuum oven for 24 h. This finding indicated that none of the officially recognized methods removed all the moisture. Data showed that many laboratories tended to give either higher or lower results than the mean of all of them in a series of 7 interlaboratory trials. Constant results, free of biases or systematic errors, are important in application of formulas for prediction of yield of cheese for purposes of yield control, but are difficult to obtain. It is proposed that results by a laboratory in interlaboratory trials be compared with those obtained by one or more reference laboratories using a method that removes all the moisture from cheese. The difference would be applied as a constant in the predictive yield formula. That difference would likely be best as a running mean of differences in an ongoing series of trials. The reference laboratories would use frozen samples for quality control to ensure uniformity of results among trials. Mean moistures of 36.10 and 36.11% were obtained on subsamples before and after freezing for 7 months.

Cheese↗
PubMedDate not supplied

Schizencephaly, consequence of a developmental vasculopathy? A clinicopathological report.

Schizencephaly was diagnosed by CT scan in a 3-month-old girl who died soon thereafter. The main neuropathological findings were the following: 1) A left frontal and a right parietal cleft were present which consisted in mesenchymal spaces taking the place of localized developmental defects of the cerebral mantel. 2) The gray matter lining the clefts was a microgyric cortical ribbon deeply infolded in the hemisphere without evidence of arrested neuronal migration. 3) However, true subependymal heterotopia were also recorded in areas distant from the microgyric ribbon. It is suggested that schizencephaly is initiated before the end of neuronal migration, at a time when the full thickness of the cerebral mantel can be easily destroyed by a localized malacic process, not later than 20 weeks of gestation. 4) Late ischemic insults to the cerebral cortex were observed, suggesting a long lasting process. Moreover, the death was due to an hematoma in the largest cleft, where atypical vessels were present. A developmental vasculopathy could be the cause for some cases of schizencephaly and could be life-threatening until the postnatal life.

Brain↗