Influence of different histories of the inoculum on lag phase and growth of Listeria monocytogenes in meat models

The aim of this study was to determine the effect of history of inoculum and preservatives on the lag phase and growth rate of Listeria monocytogenes strains in meat products packaged under modified atmosphere conditions. Inocula with different histories were added to meat models, and growth rate and lag phase of two strains of L. monocytogenes were measured at 5 and 10 degrees C. The meat model stored at 10 degrees C contained sodium lactate, but the model stored at 5 degrees C did not. The five different histories of the inocula included cold propagation, biofilm formation, and starvation. The lag phase ranged from 1 to 10 days and was affected by the history of the inoculum, whereas the growth rate was constant except for one combination of history of inoculum and strain, where growth did not start during the incubation period. In a second series of experiments, the growth rate and lag phase of the two Listeria strains and the effects of two different histories of inoculum were tested in meat models with pH 5.7 or 6.5 and increasing amounts of NaCl. The growth rate depended on salt concentration, bacterial strain, and pH, whereas lag phase duration depended on history of inoculum, salt concentration, and pH. The lag phase duration was highly dependent on the history of the inoculum, and higher amounts of preservative (NaCl) made these effects even more noticeable. The results of this study underline the importance of the effects of the history of the inoculum on lag phase duration and could be used to predict lag phase in industrial meat products.     

Analysis of noncovalent chitinase-chito-oligosaccharide complexes by infrared-matrix assisted laser desorption ionization and nanoelectrospray ionization mass spectrometry

Transferring noncovalently bound complexes from the condensed phase into the gas phase represents a challenging task due to weak intermolecular bonds that have to be maintained during the phase transition. Currently, electrospray ionization (ESI) is the standard mass spectrometric (MS) technique to analyze noncovalent complexes. Although infrared matrix-assisted laser desorption ionization (IR-MALDI)-MS also provides particular soft desorption/ionization conditions, this method has so far hardly been applied for the analysis of noncovalent complexes. In this study, we employed IR-MALDI orthogonal time-of-flight (o-TOF)-MS in combination with the liquid matrix glycerol to characterize the specific complex formation of chito-oligosaccharide (CHOS) ligands with two variants of Chitinase A (ChiA) from Serratia marcescens, the inactive E315Q mutant and the active W167A mutant, respectively. The IR-MALDI-o-TOF-MS results were compared to those obtained using nano-ESI-quadrupole (q)-TOF-MS and ultraviolet (UV)-MALDI-o-TOF-MS. Using IR-MALDI-o-TOF-MS, specific noncovalent complexes between ChiA and CHOS were detected with distributions between enzymes with bound oligosaccharides vs free enzymes that were essentially identical to those obtained by nano-ESI-q-TOF-MS. Chitinase-CHOS complexes were not detected when UV-MALDI was employed for desorption/ionization. The results show that IR-MALDI-MS can be a valuable tool for fast and simple screening of noncovalent enzyme-ligand interactions.     

Effects of adsorbed heat labile serum proteins and fibrinogen on adhesion and apoptosis of monocytes/macrophages on biomaterials

A previously established human monocyte culture protocol was used to determine the effects of varying adsorbed proteins on monocyte/macrophage adhesion and survival on dimethyl-silane (DM) or RGD modified glass coverslips. Cells were allowed to adhere for 2 h in the absence of protein or in the presence of serum, fibrinogen (Fg), heat inactivated serum (HIS), serum supplemented with Fg or HIS with Fg. Cell adhesion and apoptosis rates were determined on days 0 (2 h), 3, 7 and 10 of culture. The presence of serum alone in the initial culture was sufficient to optimize monocyte/macrophage adhesion and survival rates. Adding Fg to serum did not increase adhesion nor decrease apoptotic rates. No protein or the addition of HIS during the initial incubation period significantly decreased monocyte/macrophage adhesion and survival on both surfaces, however, the addition of Fg to HIS restored adhesion and survival rates to those seen with in the presence of serum alone on RGD surfaces. These studies demonstrate that monocyte/macrophage adhesion and survival on biomaterial surfaces are optimized by adsorbed heat labile serum proteins while adsorbed Fg plays a surface property-dependent role.     

A synthetic IgG-binding domain based on staphylococcal protein A

A synthetic IgG-binding domain based on staphylococcal proteinA was designed with the aid of sequence comparisons and computergraphic analysis. A strategy, utilizing non-palindromic restrictionsites, was used to overcome the difficulties of introducingshe-specific changes into the repetitive gene. A single mutagenizedgene fragment was polymerized to different multiplicities, andthe different gene products were expressed in Escherichia coli.Using this scheme, protein A-like proteins composed of differentnumbers of IgG-binding domains were produced. These domainswere changed to lack asparagine-glycine dipeptide sequencesas well as methionine residues and are thus, in contrast tonative protein A, resistant to treatment with hydroxylamineand cyanogen bromide.     

Reduced combustion efficiency of chlorinated compounds,resulting in higher yields of carbon monoxide

A series of experiments involving the combustion of inherently fire-retarded compounds has been performed using the DIN 53 436 furnace. Six chlorinated compounds comprising four pesticides, an organic solvent, and polyvinyl chloride (PVC) have been investigated with the focus on the combustion efficiency expressed as the CO₂/CO ratio in the fire effluent. It was found that increased chloride content in a compound resulted in decreased CO₂/CO ratio. The correlation was found to be $ \sqrt {{\rm CO}_{\rm 2} /{\rm CO}} = 0.61 \times ({\rm Cl/C)}^{- {\rm 1}} + 0.13 $. The results indicate higher concentrations of CO in the fire effluent from chlorinated compounds than from wood. Together with a release of HCI this could result in an increased toxic potency. The overall toxic hazard may or may not be increased, since (inherently) fire-retarded materials tend to have an improved fire performance.     

Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC)

Background  

The Norwegian Women and Cancer Study (NOWAC) is a national population-based cohort study with 102 443 women enrolled at age 30–70 y from 1991 to 1997. The present study was a methodological sub-study to assess the test-retest reproducibility of the NOWAC food frequency questionnaire (FFQ), and to study how measurement errors in the data can affect estimates of disease risk.     

Experimental and model assisted investigation of an operational strategy for the BPR under low influent concentrations

The behaviour of a pilot scale biological phosphorus removal process (BPR) of the alternating type was investigated during periods of low influent concentrations and increased hydraulic load. A process disturbance of this type result in an increase in the phosphate concentration level in the anoxic/aerobic reactors and in the plant effluent shortly after the influent wastewater returns to normal strength. The accumulation of phosphorus in the system was avoided by the addition of an external carbon source either to the influent or to the effluent from the anaerobic reactor in form of sodium acetate. With the help of such an addition, the internal carbon storage compounds could be maintained at a high level, which is shown by poly-hydroxy-alcanoates (PHA) measurements. Several levels of acetate addition were investigated experimentally in order to determine a minimal amount of internally stored carbon, which could ensure the stabilization of BPR during such dynamic influent conditions. Furthermore reduction of aeration time during periods of low influent concentrations was investigated. It was observed that BPR was stabilized by combining a reduction of aeration time with carbon source addition, which maintained the internal stored carbon at a higher level. This combined control action resulted in a desired high BPR activity when the normal strength of the influent wastewater was re-established. The failure of the BPR process was sometimes observed even when comparatively high concentrations of PHA could be detected and an identification of a minimal PHA level was not possible. During this investigation an extended version of the activated sludge model No. 2 (ASM2), which includes denitrification by phosphate accumulating organisms, is used for the detailed analysis of the experiments. The model predicted the phosphorus build-up after the process disturbance as well as the performance during the stabilized experiments. Assisted by the model, the investigations indicate that a PHA limitation is not the only factor affecting the recovery of the BPR process during periods of low influent concentrations.     

Exploring Viral Interference Using Peptides: Molecular Determinants of HIV-1 Inhibition by a Peptide Derived from Human Pegivirus-1 Envelope Protein E2

Co-infection with the human pegivirus 1 (HPgV-1) often has a beneficial effect on disease progression in HIV-1-infected individuals. Several HPgV-1 proteins and peptides, including a 20-mer peptide (P6-2) derived from the N-terminal region of the HPgV-1 surface protein E2, have been associated with this phenomenon, which is referred to as viral interference. We identified the cysteine residues, the hydrophobic core tetrapeptide, as well as the C-terminal negative charge as key factors for the HIV-1 inhibitory activity of P6-2. Analysis of mutations in P6-2-resistant HIV-1 indicated a binding site for the peptide in the HIV-1 envelope glycoprotein gp120. In fact, P6-2 was shown to bind to soluble gp120, as well as to a peptide presenting the gp120 V3 loop. Furthermore, the HIV-1 inhibitory activity of P6-2 could be revoked by the V3 loop peptide, thus indicating a molecular mechanism that involves interaction of P6-2 with the gp120 V3 loop.