Impact of preheating on the behavior of Listeria monocytogenes in a broth that mimics Camembert cheese composition

The effect of preheating on the survival of L. monocytogenes in Richard's broth, which mimics the composition of Camembert cheese composition, was examined. Experiments were carried out to reproduce contamination of cheese with environmental heat-stressed cells of L. monocytogenes surviving hot-cleaning procedures. Cells in mid-log phase were heated for 30 min at 56 degrees C before being inoculated into Richard's broth. The pHs and temperatures of Richard's broth were chosen to recreate the conditions of curd dripping (pH 5, 25 degrees C), of the beginning of cheese ripening (pH 5, 12 degrees C), and of the beginning (pH 5, 4 degrees C) and the end (pH 7, 4 degrees C) of cheese storage. Immediately after heat treatment, the viability loss was especially high for strain 306715, which exhibited only 0.6% +/- 0.2% survival, compared with 22% +/- 8.7% for strain EGD. The percentages of the surviving heated cells that were injured were 93% +/- 8% for strain 306715 and 98% +/- 3% for strain EGD. The destruction of the surviving L. monocytogenes cells was accelerated when they encountered the pH and temperature conditions of Camembert cheese during manufacturing, ripening, and cold storage (pH 5 at 25, 12, and 4 degrees C, respectively). The multiplication of the surviving heated cells was retarded under favorable growth conditions similar to those of storage by the distributor and the consumer (pH 7 at 4 and 12 degrees C, respectively).

Analysis by two-dimensional electrophoresis of proteins secreted by sheep ovarian follicles: effects of the FecB gene, follicle size and atresia

Proteins secreted by sheep ovarian follicles at different stages of maturation (small healthy, large healthy or large atretic) and originating from ewes with different ovulation rates (homozygous carriers or noncarriers of the FecB gene) were analysed by two-dimensional electrophoresis (PAGE) followed by computerized image analysis. Follicles were incubated intact for 1 h to assess steroidogenesis, and then incubated for 24 h in the presence of [35S]methionine. Secreted proteins were then resolved by iso-electric focusing followed by migration on 10% acrylamide slab gels and fluorography. Incorporation of label into proteins was similar irrespective of genetic type or health status of the follicles (4-6%). Small follicles incorporated significantly less (P < 0.05) label. Over 100 spots were detected on the fluorographs. The presence of the FecB gene induced qualitative and quantitative changes in the follicular protein patterns. Frequency of detection of spots 116 and 129 was significantly higher (P < 0.01) in Fec+Fec+ compared with FecBFecB follicles (80% versus 8%). In addition, amounts of proteins present in spots 2 and 12 were increased in FecBFecB follicles, while those in spots 9 and 21 were decreased. Size and atresia affected protein patterns only quantitatively. Increased amounts of proteins in spots 1, 10, 38, 44 and 113 were associated with atresia (P < 0.05). Follicle enlargement was associated with increased (P < 0.05) amounts of proteins in spots 5 and 6 and decreased amounts of proteins in spot 16. Amounts of three proteins (33, 40 and 58) were related positively to oestradiol production in vitro before labelling.

Histocompatible miniature, boar model: selection of transformed cell lines of B and T lineages producing retrovirus

A lymphoblastoid cell line (B1) was isolated in culture following a brief exposure to 5-azacytidine from peripheral-blood mononuclear cells of a boar previously injected with cells (Shimozuma) producing porcine retrovirus (Tsukuba-1) and suffering a severe non-neoplastic syndrome at autopsy. B1 cell line and 5 of its sublines were propagated for more than 100 generations, retaining doubling times comprised between 16.8 and 27.5 hr and growing readily in agarose or agar (plating efficiency: 5 to 50%). Karyotype analyses showed that 4 sublines were nearly diploid, except for cells of L14, which displayed a monosomy affecting chromosome 18 pair. Two sublines (L35 and L45) were considered as being of T-cell lineage, since MSA, antigen was observed on the surface of approximately 30% of cells. Three sublines (L23, L14 and L52) were considered of B-cell lineage, since membrane immunoglobulins were observed on the cell surface. In addition, sublines L23 and L52 were actively secreting immunoglobulin of mu isotype. Retrovirus particles were evidenced in gradient-purified preparation of 200-fold-concentrated cell culture supernatants of the B1 cell line, L14, L35 and L52 sublines, using both a reverse transcriptase activity assay and electron microscopic observation. These cell lines can be used to select for porcine retrovirus variants with transforming potential for lymphocytes of B and T lineages.

Purification and Characterization of an Aminopeptidase from Lactococcus lactis subsp. cremoris AM2

An aminopeptidase was purified from cell extracts of Lactococcus lactis subsp. cremoris AM2 by ion-exchange chromatography. After electrophoresis of the purified enzyme in the presence or absence of sodium dodecyl sulfate, one protein band was detected. The enzyme was a 300-kilodalton hexamer composed of identical subunits not linked by disulfide bridges. Activity was optimal at 40°C and pH 7 and was inhibited by classical thiol group inhibitors. The aminopeptidase hydrolyzed naphthylamide-substituted amino acids, as well as dipeptides and tripeptides. Longer protein chains such as the B chain of insulin were hydrolyzed, but at a much slower rate. The Michaelis constant ( K m ) and the maximal rate of hydrolysis ( V max ) were, respectively, 4.5 mM and 3,600 pkat/mg for the substrate l -histidyl-β-naphthylamide. Amino acid analysis showed that the enzyme contained low levels of hydrophobic residues. The partial N-terminal sequence of the first 19 residues of the mature enzyme was determined. Polyclonal antibodies were obtained from the purified enzyme, and after immunoblotting, there was no cross-reaction between these antibodies and other proteins in the crude extract.