Modified Acid Phosphatase Assay for Assessing the Extent of Heating of Canned Picnics and Hams: Interlaboratory Study

Determination of acid phosphatase (E.C. 3.1.3.2.) activity in meat and meat products Is based on spectrophotometric measurement of free phenol released from phenyl phosphate substrate during enzyme catalysis under prescribed conditions. Precision parameters of a new modified phosphatase assay, proposed for determination of extent of heating of canned picnics and hams, were evaluated in an interlaboratory study with 10 (1 German, 2 Italian, and 7 Hungarian) participating laboratories. The test materials were 5 lean meat batters subjected to different heat treatments (i.e., with different levels of phosphatase activity). The materials were presented to participants as 10 randomly coded samples (2 blind replicates of each material). The interlaboratory study was then repeated with 3 test materials and 2 blind replicates (3 × 2) prepared in the same way. The repeatability relative standard deviation (RSDr), outliers excluded, varied from 2.2 to 10.7%, and the reproducibility relative standard deviation (RSDR) varied from 12.6 to 25.3%. Results were compared with other data in the literature. The sensitivity of the new modified phosphatase assay was also compared with that of the original procedure described in USDA Chemistry Laboratory Guidebook. A higher sensitivity was observed for the method described in this paper. However, the method’s reproducibility was poorer than that of common analytical methods. Although high, the variability may still be acceptable for determining phosphatase activity to assess extent of heat treatment of canned picnics and hams.

Tunable spin polarization and superconductivity in engineered oxide interfaces

Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials' engineering tool in today's semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides. Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (TFM = 6-8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin-orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.

Dimethyl fumarate selectively reduces memory T cells in multiple sclerosis patients

BACKGROUND

Dimethyl fumarate (DMF) alters the phenotype of circulating immune cells and causes lymphopenia in a subpopulation of treated multiple sclerosis (MS) patients.

OBJECTIVE

To phenotypically characterize circulating leukocytes in DMF-treated MS patients.

METHODS

Cross-sectional observational comparisons of peripheral blood from DMF-treated MS patients (n = 17 lymphopenic and n = 24 non-lymphopenic), untreated MS patients (n = 17) and healthy controls (n = 23); immunophenotyped using flow cytometry. Longitudinal samples were analyzed for 13 DMF-treated patients.

RESULTS

Lymphopenic DMF-treated patients had significantly fewer circulating CD8(+) and CD4(+) T cells, CD56(dim) natural killer (NK) cells, CD19(+) B cells and plasmacytoid dendritic cells when compared to controls. CXCR3(+) and CCR6(+) expression was disproportionately reduced among CD4(+) T cells, while the proportion of T-regulatory (T-reg) cells was unchanged. DMF did not affect circulating CD56(hi) NKcells, monocytes or myeloid dendritic cells. Whether lymphopenic or not, DMF-treated patients had a lower proportion of circulating central and effector memory T cells and concomitant expansion of naïve T cells compared to the controls.

CONCLUSIONS

DMF shifts the immunophenotypes of circulating T cells, causing a reduction of memory cells and a relative expansion of naïve cells, regardless of the absolute lymphocyte count. This may represent one mechanism of action of the drug. Lymphopenic patients had a disproportionate loss of CD8(+) T-cells, which may affect their immunocompetence.

High-T(c) Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low T(c). We report the occurrence of high T(c) superconductivity in the bilayer CaCuO(2)/SrTiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO(2)/SrTiO(3) interface must be realized between the Ca plane of CaCuO(2) and the TiO(2) plane of SrTiO(3). Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. A detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO(2) unit cells close to the interface with SrTiO(3). The results obtained for the CaCuO(2)/SrTiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems.

A novel polymerase chain reaction (PCR) - denaturing gradient gel electrophoresis (DGGE) for the identification of Micrococcaceae strains involved in meat fermentations. Its application to naturally fermented Italian sausages

A new molecular method consisting of polymerase chain reaction (PCR) amplification and denaturing gradient gel electrophoresis (DGGE) of a small fragment from the 16S rRNA gene identified the Micrococcaceae strains isolated from natural fermented Italian sausages. Lactic acid bacteria, total aerobic mesophilic flora, Enterobacteriaceae and faecal enterococci were also monitored. Micrococcaceaea control strains from international collections were used to optimise the method and 90 strains, isolated from fermented sausages, were identified by biochemical tests and PCR-DGGE. No differences were observed between the methods used. The results reported in this paper prove that Staphylococcus xylosus is the main bacterium involved in fermented sausage production, representing, from the tenth day of ripening, the only Micrococcaceaea species isolated.

Application of automated ribotyping to support the evaluation of Listeria monocytogenes sources in a Taleggio cheese producing plant

In March 2005, Listeria monocytogenes was detected on the rinds of Taleggio cheeses produced in an Italian plant. To identify the pathogen source, 154 rinds of cheeses that had been manually and automatically salinated and 52 environmental swabs collected from salting equipment, ripening cloths, and ripening boxes were tested for L. monocytogenes. Twenty-seven strains isolated from cheese samples and 16 strains isolated from environmental samples were genotyped by EcoRI and PvuII automated ribotyping. The microbiological results revealed a significant incidence of contamination of cheeses that were automatically salinated and contamination on the salting equipment, ripening cloths, and boxes. All cheese and environmental strains had the same EcoRI and PvuII ribotyping profiles, designated 153-204-S5 and 153-210-S-2, respectively. The only exception were three Taleggio strains, isolated from the same lot of product, that had EcoRI and PvuII ribotyping profiles designated 153-289-S6 and 153-214-S-5, respectively. Strains with EcoRI profile 153-204-S5 were classified as DUP-ID 1045 and serotype 1/2a, whereas strains with EcoRI profile 153-289-S6 were classified as DUP-ID 1034 and serotype 1/2b. The microbiological and molecular typing data collected in this study suggest that the source of the L. monocytogenes contamination in the Taleggio plant under study was the automated salting equipment. The isolate DUP-IDs were used to trace the introduction of potentially dangerous strains, such as those characterized as DUP-ID 1034, in the processing plant.

A molecular method to detect Bacillus cereus from a coffee concentrate sample used in industrial preparations

AIMS

The aim of this work was to develop specific primers which are able to detect Bacillus cereus in a coffee concentrate sample.

METHODS AND RESULTS

A pre-PCR step to clean the DNA, used for PCR, was developed to avoid PCR inhibition by Maillard products. The combination of centrifugation and washing the pellet, employing EDTA and water, before DNA extraction improved the detection of low numbers of B. cereus cells (10 cells ml-1). The development of specific primers enabled to detect low numbers of B. cereus without the need of a pre-enrichment step.

CONCLUSIONS

The data obtained demonstrated the specificity and the sensitivity of the primers that could be used to check the presence of B. cereus in different food products, avoiding the need for labourious and time-consuming culture-based techniques.

SIGNIFICANCE AND IMPACT OF THE STUDY

The method could help food microbiologists to check food samples quickly for the presence of B. cereus.

Verocytotoxin-producing Escherichia coli in foodstuffs of animal origin

While much research effort has been targeted at the verocytotoxin-producing Escherichia coli (VTEC) serotype O157:H7, it is becoming more evident that other VTEC serotypes can also be associated with human foodborne disease. An increasing number of these non-O157 serotypes have been isolated from food sources and from humans suffering from haemolytic-uraemic syndrome and diarrhoea. The aim of our work was to investigate the prevalence of VTEC O157 and non-O157 in foodstuffs of animal origin using two rapid enzymatic procedures. Various types of food samples, 352 in total, were tested: 233 with the Premier EHEC, a screening test which directly detects the presence of verocytotoxin, regardless of serotype, while 119 of these with the Vidas ECO, which is a specific screening test for E. coli O157:H7, together with the Premier EHEC. Two samples were positive for VTEC, one of serogroup O126 and the other was non-serotypable. Another sample was positive in the test specific for E. coli O157:H7, but was not confirmed by culture. This study suggests that VTEC strains are not prevalent in Italy, and that the isolation of serogroup O157 is relatively infrequent. This leads us to conclude that there is little chance of exposure to pathogen for the average consumer in Italy.

Clinical and serological associations of ribosomal P autoantibodies in systemic lupus erythematosus: prospective evaluation in a large cohort of Italian patients

OBJECTIVE

To verify the association of ribosomal anti-P antibodies (anti-P), as detected by a sensitive ELISA, with serological findings and clinical manifestations, including neuropsychiatric involvement evaluated according to the American College of Rheumatology (ACR) nomenclature, in a large cohort of patients with systemic lupus erythematosus (SLE).

METHODS

Anti-P were evaluated in the serum of 149 consecutive Italian SLE patients by an ELISA using a multiple antigen peptide carrying four copies of a common P0, P1 and P2 epitope. A complete laboratory evaluation and clinical examination were performed in each patient. In addition, all patients underwent an accurate neuropsychiatric and neuropsychological assessment performed by trained specialists according to the 1999 ACR suggestions.

RESULTS

Serum anti-P were detected in 18/149 patients (12.1%). The anti-P prevalence was similar (11.7%) when the analysis was performed in a larger series of sera including 82 additional SLE patients, who were not included in the clinical study. The age of anti-P-positive patients at disease onset was less than 33 yr and, in comparison with the anti-P-negative patients, these patients showed more active disease activity and a higher prevalence of photosensitivity and malar and discoid rash. A strong association between IgG anticardiolipin antibodies and anti-P was also found. However, anti-P were associated with neither neuropsychiatric syndromes nor cognitive impairment.

CONCLUSION

This study does not seem to confirm the described association of anti-P with SLE neuropsychiatric manifestations. However, it supports the anti-P association with different skin manifestations as well as the presence of anticardiolipin in a subset of patients with SLE characterized by early disease onset.

Identification, molecular cloning and functional characterization of NKp46 and NKp30 natural cytotoxicity receptors in Macaca fascicularis NK cells

Natural killer (NK) cell recognition and function in humans is regulated by multiple cell surface receptors. The "on" signal leading to NK cell triggering is primarily mediated by natural cytotoxicity receptors (NCR). Analysis of NK cells in primate animal models is of particular relevance because NK cells may play an essential role in host defenses against infections. We analyzed Macaca fascicularis PBMC and in vitro-derived NK cell populations and clones by cytofluorometry, using a wide panel of mAb, and by cytolytic activity assays. In addition, RT-PCR strategy and transient transfections were used to isolate M. fascicularis NCR. NCR-specific mAb reactivity (anti-NKp46 and anti-NKp30) was present on M. fascicularis PBMC and on NK cell cultures. Macaque NCR were functional in both redirected killing and in mAb-mediated masking assays. Cloning of macNKp46 and macNKp30 NCR homologous genes showed a high sequence similarity (86 % and 88 %, respectively) with their human counterparts. Attempts at identifying NKp44 surface reactivity and at cloning the macaque homologue were unsuccessful. NKp46 and NKp30 NCRs, but not NKp44, are highly conserved in M. fascicularis NK cells. This suggests the possibility of a staged appearance of the NCR during phylogenesis and provides a useful tool for the study of natural immunity correlates of protection in primate SIV/SHIV infection models.

Denaturing gradient gel electrophoresis analysis of the 16S rRNA gene V1 region to monitor dynamic changes in the bacterial population during fermentation of Italian sausages

In this study, a PCR-denaturing gradient gel electrophoresis (DGGE) protocol was used to monitor the dynamic changes in the microbial population during ripening of natural fermented sausages. The method was first optimized by using control strains from international collections, and a natural sausage fermentation was studied by PCR-DGGE and traditional methods. Total microbial DNA and RNA were extracted directly from the sausages and subjected to PCR and reverse transcription-PCR, and the amplicons obtained were analyzed by DGGE. Lactic acid bacteria (LAB) were present together with other organisms, mainly members of the family Micrococcaceae and meat contaminants, such as Brochothrix thermosphacta and Enterococcus sp., during the first 3 days of fermentation. After 3 days, LAB represented the main population, which was responsible for the acidification and proteolysis that determined the characteristic organoleptic profile of the Friuli Venezia Giulia fermented sausages. The PCR-DGGE protocol for studying sausage fermentation proved to be a good tool for monitoring the process in real time, and it makes technological adjustments possible when they are required.

Identification of commercial fish species belonging to the orders pleuronectiformes and gadiformes: library of isoelectric focusing patterns

Isoelectric focusing in polyacrylamide gel was used to establish an identification archive of fish species belonging to the orders Pleuronectiformes, or flat fish, and Gadiformes, or gadoid fish. The 2 orders include species of different commercial value and interest that are frequently requested in European fish markets, but are susceptible to substitution either because they are morphologically similar or because they arrive on the markets already filleted or sliced. The sarcoplasmic protein profiles are species-specific and reproducible. The use of densitometry and image analysis coupled with a simple computer program overcomes the subjective evaluation of the patterns, making it possible to identify species correctly.

Activating receptors and coreceptors involved in human natural killer cell-mediated cytolysis

Natural killer cells can discriminate between normal cells and cells that do not express adequate amounts of major histocompatibility complex (MHC) class I molecules. The discovery, both in mouse and in human, of MHC-specific inhibitory receptors clarified the molecular basis of this important NK cell function. However, the triggering receptors responsible for positive NK cell stimulation remained elusive until recently. Some of these receptors have now been identified in humans, thus shedding some light on the molecular mechanisms involved in NK cell activation during the process of natural cytotoxicity. Three novel, NK-specific, triggering surface molecules (NKp46, NKp30, and NKp44) have been identified. They represent the first members of a novel emerging group of receptors collectively termed natural cytotoxicity receptors (NCR). Monoclonal antibodies (mAbs) to NCR block to differing extents the NK-mediated lysis of various tumors. Moreover, lysis of certain tumors can be virtually abrogated by the simultaneous masking of the three NCRs. There is a coordinated surface expression of the three NCRs, their surface density varying in different individuals and also in the NK cells isolated from a given individual. A direct correlation exists between the surface density of NCR and the ability of NK cells to kill various tumors. NKp46 is the only NCR involved in human NK-mediated killing of murine target cells. Accordingly, a homologue of NKp46 has been detected in mouse. Molecular cloning of NCR revealed novel members of the Ig superfamily displaying a low degree of similarity to each other and to known human molecules. NCRs are coupled to different signal transducing adaptor proteins, including CD3 zeta, Fc epsilon RI gamma, and KARAP/DAP12. Another triggering NK receptor is NKG2D. It appears to play either a complementary or a synergistic role with NCRs. Thus, the triggering of NK cells in the process of tumor cell lysis may often depend on the concerted action of NCR and NKG2D. In some instances, however, it may uniquely depend upon the activity of NCR or NKG2D only. Strict NKG2D-dependency can be appreciated using clones that, in spite of their NCR(dull) phenotype, efficiently lyse certain epithelial tumors or leukemic cell lines. Other triggering surface molecules including 2B4 and the novel NKp80 appear to function as coreceptors rather than as true receptors. Indeed, they can induce natural cytotoxicity only when co-engaged with a triggering receptor. While an altered expression or function of NCR or NKG2D is being explored as a possible cause of immunological disorders, 2B4 dysfunction has already been associated with a severe form of immunodeficiency. Indeed, in patients with the X-linked lymphoproliferative disease, the inability to control Epstein-Barr virus infections may be consequent to a major dysfunction of 2B4 that exerts inhibitory instead of activating functions.

Human natural killer cell function and receptors

Recent years have witnessed major progress in our understanding of the molecular mechanisms regulating natural killer cell (NK cell) function. These advances stem primarily from the discovery of a number of receptors specific for major histocompatibility complex (MHC) class I and, more recently, of the activating receptors and coreceptors responsible for natural cytotoxicity. Important studies performed over the past year have allowed us to define the evolution of the MHC-specific inhibitory receptors by comparative analysis in different species. The roles of the 'activating natural cytotoxicity receptors', NKG2D and certain coreceptors in the lysis of different tumors have been defined in detail. The mechanism by which the 2B4 coreceptor renders patients with X-linked lymphoproliferative disease unable to control Epstein-Barr virus has been elucidated. Inhibitory receptors identified in NK cells may also be expressed by normal and leukemic myeloid cells, in which they can block cell proliferation and survival. It has also become clear that viruses such as cytomegalovirus have evolved strategies to interfere with NK-cell function to protect themselves from NK-mediated attack.

Human natural killer cell receptors and co-receptors

In the absence of sufficient signaling by their HLA class I-specific inhibitory receptors, human natural killer (NK) cells become activated and display potent cytotoxicity against cells that are either HLA class I negative or deficient. This indicates that the NK receptors responsible for the induction of cytotoxicity recognize ligands on target cells different from HLA class I molecules. On this basis, the process of NK-cell triggering can be considered as a mainly non-MHC-restricted mechanism. The recent identification of a group of NK-specific triggering surface molecules has allowed a first series of pioneering studies on the functional/molecular characteristics of such receptors. The first three members of a receptor family that has been termed natural cytotoxicity receptors (NCR) are represented by NKp46, NKp44 and NKp30. These receptors are strictly confined to NK cells, and their engagement induces a strong activation of NK-mediated cytolysis. A direct correlation exists between the surface density of NCR and the ability of NK cells to kill various target cells. Importantly, mAb-mediated blocking of these receptors has been shown to suppress cytotoxicity against most NK-susceptible target cells. However, the process of NK-cell triggering during target cell lysis may also depend on the concerted action of NCR and other triggering receptors, such as NKG2D, or surface molecules, including 2B4 and NKp80, that appear to function as co-receptors rather than as true receptors. Notably, a dysfunction of 2B4 has been associated with a severe form of immunodeficiency termed X-linked lymphoproliferative disease. Future studies will clarify whether also the altered expression and/or function of other NK-triggering molecules may represent a possible cause of immunological disorders.

Role of NKG2D in tumor cell lysis mediated by human NK cells: cooperation with natural cytotoxicity receptors and capability of recognizing tumors of nonepithelial origin

NKG2D is a recently described activating receptor expressed by both NK cells and CTL. In this study we investigated the role of NKG2D in the natural cytolysis mediated by NK cell clones. The role of NKG2D varied depending on the type of target cells analyzed. Lysis of various tumors appeared to be exclusively natural cytotoxicity receptors (NCR) dependent. In contrast, killing of another group of target cells, including not only the epithelial cell lines HELA and IGROV-1, but also the FO-1 melanoma, the JA3 leukemia, the Daudi Burkitt lymphoma and even normal PHA-induced lymphoblasts, involved both NCR and NKG2D. Notably, NK cell clones expressing low surface densities of NCR (NCR(dull)) could lyse these tumors in an exclusively NKG2D-dependent fashion. Remarkably, not all of these targets expressed MICA/B, thus implying the existence of additional ligands recognized by NKG2D, possibly represented by GPI-linked molecules. Finally, we show that the engagement of different HLA class I-specific inhibitory receptors by either specific antibodies or the appropriate HLA class I ligand led to inhibition of NKG2D-mediated NK cell triggering.

DNase I mediates internucleosomal DNA degradation in human cells undergoing drug-induced apoptosis

Internucleosomal DNA fragmentation following the activation of endonucleases is the common end point of apoptosis. DNase I, a Ca(2+) / Mg(2+)-dependent endonuclease ubiquitously expressed in mammalian tissues, is believed to play a role in this process. To analyze the in vivo function of this enzyme in human cells, we have generated a cell line with targeted disruption of the DNase I gene, as well as several stable cell lines which overexpress the DNase I gene. Inactivation of the human DNase I gene was obtained in the Jurkat T cell clone JA3, characterized by high susceptibility to apoptotic cell death induced by pharmacological stimuli. JA3 cells, after disruption of the DNase I gene, became resistant to apoptotic stimuli. DNase I was overexpressed in the human cell lines JA3, K562 (erythroleukemia), M 14 (melanoma) and CEM (T cell lymphoma). Remarkably, stable overexpression of DNase I gene resulted in accelerated apoptosis in JA3 cells and induced apoptosis in K562, CEM and M14 cell lines, which are otherwise resistant to internucleosomal DNA degradation following pharmacological stimuli. Our study provides the first in vivo evidence that DNase I mediates internucleosomal DNA degradation in human cells undergoing drug-induced apoptosis.

CD4(+) cutaneous T-cell lymphoma cells express the p140-killer cell immunoglobulin-like receptor

Tumor cells of patients with cutaneous T-cell lymphoma (CTCL) have the cell surface phenotype of mature T-helper lymphocytes, and it may be impossible to differentiate them from nonmalignant lymphocytes in skin and blood. Until now, no specific cell membrane marker of CTCL has been reported. In the current study, it is reported for the first time that CTCL cells express the major histocompatibility complex class I binding p140-killer cell immunoglobulin-like receptor, which has been described on a minor subset of natural killer lymphocytes and on a marginal circulating CD8(+) T lymphocyte subset. Interestingly, the molecular characterization of this KIR expressed by CTCL allowed us to isolate a novel allelic form of p140-KIR3DL, resulting in 4 amino acid substitutions, 3 in the extracellular immunoglobulin-like domain of the protein and one in the cytoplasmic region. This finding is likely to be important both for the pathophysiology and for the clinical treatment of patients with CTCL.

Human natural killer cell activating receptors

Natural killer (NK) cells were poorly characterized until 10 years ago and few molecules expressed on their cell surface were known. Now the situation has changed dramatically, since a plethora of receptors characterized by opposite functions have been functionally and molecularly defined. NK cells express clonally distributed inhibitory receptors specific for different groups of HLA class I alleles, thus protecting normal cells from NK-mediated lysis. On the contrary, various activating receptors are involved in triggering of NK-mediated natural cytotoxicity. Their engagement induces human NK cells to kill target cells that are either HLA class I-negative or -deficient. Here a brief description of the activating receptors and coreceptor and of their ligand(s) is given.

A multiplex-PCR method to detect enterohemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli in artificially contaminated foods

In view of the considerable public health risk of the enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli, a multiplex-PCR based method was used for the amplification of the slt genes and of the eaeA gene. Three pairs of primers, different from the oligonucleotides previously used by other authors, were exploited for the amplification. Different E. coli serotypes were tested with the optimized protocol. Fifty three artificially contaminated samples and sixty naturally contaminated samples were processed with the multiplex-PCR. All the artificially contaminated samples gave positive results independently of the number of cells inoculated. On the contrary, the naturally contaminated samples were all negative. The results obtained from this experiment demonstrated that this protocol could be used for monitoring the spread of these organisms in food.

Role of Nd/Ba disorder on the penetration depth of Nd(1+x)Ba(2-x)Cu(3)O(7-delta) thin films

We report on a study on the effect of Nd/Ba disorder on the ab-plane penetration depth of epitaxial Nd(1+x)Ba(2-x)Cu(3)O(7-delta) thin films. While in stoichiometric samples lambda(T) at low temperature is linear, Nd-rich films exhibit a quadratic law. For low Nd excess (x<0.04), a satisfying fit is obtained using the "dirty" d-wave model assuming that Nd ions at Ba sites act as strong scattering centers. At high x (x>0.15) the data are explained if Nd/Ba disorder becomes less effective as a source of scattering. The effect of localization has been discussed to account for the experimental results.

Temperature gradient gel electrophoresis of the amplified product of a small 16S rRNA gene fragment for the identification of Listeria species isolated from food

The development of a rapid method for the identification of Listeria spp. is described. It is based on the polymerase chain reaction amplification of a small fragment from the 16S rRNA gene followed by temperature gradient gel electrophoresis. Forty-five strains of Listeria spp. (Listeria monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, and Listeria welshimeri) were used for the optimization of the protocol. No differences were observed between the results of the identification of the strains tested using traditional methods and those obtained by polymerase chain reaction-temperature gradient gel electrophoresis analysis.

Development and evaluation of a PCR-microplate capture hybridization method for direct detection of verotoxigenic Escherichia coli strains in artificially contaminated food samples

For the purpose of detecting, directly in food, verotoxigenic Escherichia coli, a microplate hybridization method for the detection of PCR products from the SLT I and SLT II genes, was developed and evaluated. Two pairs of primers and two probes, specific for the SLT I gene and for the SLT II gene, were designed and tested. For the strains containing both genes, two PCR products of different molecular weights were obtained, whereas when only one gene was present only one fragment resulted from PCR. The use of the biotin-labeled probes allowed the immobilization of the PCR products in the microtiter plate wells and by this means their detection was possible using an ELISA-based technique. Forty artificially contaminated and fifty naturally contaminated food samples were analyzed by using the PCR-microplate hybridization technique developed in this study. All the artificially contaminated food samples were positive, independently of the number of cells inoculated before the enrichment step, whereas the naturally contaminated food samples were all negative.

Development of a rapid method for the identification of Lactobacillus spp. isolated from naturally fermented italian sausages using a polymerase chain reaction-temperature gradient gel electrophoresis

A rapid method for the identification of Lactobacillus spp. isolated from naturally fermented Italian sausages was developed. It is based on the amplification of a small fragment from the 16S rRNA gene followed by temperature gradient gel electrophoresis (TGGE). Lactobacillus sakei, L. curvatus, L. alimentarius, L. casei, L. plantarum and L. brevis, obtained from International Collections, were used to optimize the method. Thiry-nine strains of Lactobacillus spp. were isolated from naturally fermented sausages and, after traditional identification, were tested by the PCR-TGGE protocol developed. No differences were observed comparing the results obtained, apart from five strains identified as L. curvatus that showed a PCR-TGGE profile identical to L. sakei.

Molecular and functional characterization of IRp60, a member of the immunoglobulin superfamily that functions as an inhibitory receptor in human NK cells

In this study we describe the functional and molecular characterization of IRp60 (inhibitory receptor protein 60), an inhibitory receptor expressed on all human NK cells. The IRp60 molecule has been identified by the generation of three novel monoclonal antibodies (mAb). Cross-linking of IRp60 by specific mAb strongly inhibits the spontaneous cytotoxicity of NK cells as well as the NK-mediated cytolytic activity induced via different non-HLA-specific or HLA-specific activating receptors. IRp60 is a 60-kDa glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates with the SH2-containing phosphatases SHP-1 and SHP-2. The IRp60 gene is located on human chromosome 17 and encodes a molecule belonging to the immunoglobulin (Ig) superfamily characterized by a single V-type Ig-like domain in the extracellular portion. The cytoplasmic tail contains three classical immunoreceptor tyrosine-based inhibitory motifs. Southern blot analysis revealed cross-hybridization with monkey and mouse genomic DNA, thus suggesting that IRp60 may be conserved among different species. Moreover, based on the use of different anti-IRp60 mAb, we could identify two IRp60 allelic variants. Since IRp60 is also expressed by other cell types, including T cell subsets, monocytes and granulocytes, it may play a more general role in the negative regulation of different leukocyte populations.

P49, a putative HLA-G1 specific inhibitory NK receptor belonging to the immunoglobulin Superfamily

NK cells display several killer inhibitory receptors (KIRs) specific for different alleles of major histocompatibility complex (MHC) class I molecules. A family of KIRs are represented by type I transmembrane proteins belonging to the Immunoglobulin Superfamily (Ig-SF). In the present study we describe a cDNA, termed cl.15.212, that encodes for a type I transmembrane protein displaying approximately 50% sequence homology with other Ig-SF members. The protein encoded by cl.15.212 (termed p49 according to its apparent molecular weight of 49 kDa) is characterized by two extracellular Ig-like domains, a 115-amino acid cytoplasmic tail containing a single immuno-receptor tyrosine-based inhibitory motif (ITIM) typical of KIR. Different from the other KIRs, the cl.15.212 transcript is expressed by all NK cells and by a fraction of T-cell clones expressing KIR. To determine the specificity of the cl.15.212-encoded receptor, we generated a chimeric protein, formed by the ectodomain of p49 and the Fc portion of human IgG1 (p49-Fc). Soluble molecules bound efficiently to LCL721.221 (221) cells transfected with HLA-G1, -A3, -B46 alleles and weakly to the -B7 allele. On the other hand, they did not bind to 221 cells either untransfected or transfected with HLA-A2, -B51, -Cw3, or-Cw4.

Demonstration of viable Chlamydia pneumoniae in atherosclerotic plaques of carotid arteries by reverse transcriptase polymerase chain reaction

The presence of Chlamydia pneumoniae in atheromas has been demonstrated in several studies. Culture of the organism from arterial tissue has been difficult. We report the use of a reverse transcriptase polymerase chain reaction to detect viable Chlamydia pneumoniae in carotid atheromas. We analyzed 30 patients (14 females, mean age 69.6 +/- 8.8 years) who underwent surgery for the removal of atherosclerotic plaques from carotid arteries. During surgery, samples of lingual vein and superior thyroideal artery were also taken. We applied two molecular biology techniques to the carotid plaques on lingual vein or thyroideal artery samples: 1) polymerase chain reaction (PCR) and 2) reverse transcriptase-PCR (RT-PCR) for the detection of bacterial mRNA, employing PCR primers designed to detect a fragment of the 16S rRNA gene. Blood samples were obtained from the patients for determination of Chlamydia pneumoniae IgG, IgA, and IgM antibody titers by a microimmunofluorescence technique. The results of the present study confirmed the presence of viable Chlamydia pneumoniae in atheromas and support the hypothesis that the organism may be an active factor in the pathogenesis of atherosclerosis.

Inhibitory receptors sensing HLA-G1 molecules in pregnancy: decidua-associated natural killer cells express LIR-1 and CD94/NKG2A and acquire p49, an HLA-G1-specific receptor

Trophoblastic cells lack classical HLA class I and class II molecules but express HLA-G1. Although this may prevent allorecognition by maternal T cells, it renders trophoblastic cells potentially susceptible to lysis by natural killer (NK) cells. As shown here, only a fraction of peripheral-blood NK cells in pregnant women express the HLA-G1-specific CD94/NKG2A and/or LIR-1 receptors. However, all NK cells isolated from maternal decidua during the first trimester expressed either one or both of these receptors. Perhaps more importantly, a fraction of cells expressed p49, an HLA-G1-specific inhibitory receptor, undetectable in peripheral-blood NK cells. p49 was expressed on virtually all NK cells isolated from placenta at term. Functional analyses revealed that the HLA class I-negative 221 lymphoblastoid cell line transfected with HLA-G1 was only partially protected from lysis by peripheral-blood NK cells isolated from pregnant women, whereas it was fully protected from decidual NK cells. As indicated by the addition of specific antibodies to cytolytic tests, all the above receptors contributed to HLA-G1 recognition by decidual NK cells, although p49 would appear to play a predominant role.

NKp44, a triggering receptor involved in tumor cell lysis by activated human natural killer cells, is a novel member of the immunoglobulin superfamily

Surface receptors involved in natural killer (NK) cell triggering during the process of tumor cell lysis have recently been identified. Of these receptors, NKp44 is selectively expressed by IL-2- activated NK cells and may contribute to the increased efficiency of activated NK cells to mediate tumor cell lysis. Here we describe the molecular cloning of NKp44. Analysis of the cloned cDNA indicated that NKp44 is a novel transmembrane glycoprotein belonging to the Immunoglobulin superfamily characterized by a single extracellular V-type domain. The charged amino acid lysine in the transmembrane region may be involved in the association of NKp44 with the signal transducing molecule killer activating receptor-associated polypeptide (KARAP)/DAP12. These molecules were found to be crucial for the surface expression of NKp44. In agreement with data of NKp44 surface expression, the NKp44 transcripts were strictly confined to activated NK cells and to a minor subset of TCR-gamma/delta+ T lymphocytes. Unlike genes coding for other receptors involved in NK cell triggering or inhibition, the NKp44 gene is on human chromosome 6.

A highly sensitive and fast non-radioactive method for the detection of polymerase chain reaction products from Salmonella serovars, such as Salmonella typhi, in blood specimens

A polymerase chain reaction based test was developed for the detection of Salmonella spp. in blood specimens. After amplification of a 389 bp-polymerase chain reaction product from the invA gene, a microtiter plate hybridization assay was performed. The protocol described allowed the detection of six to seven copies of the Salmonella typhi genome, as determined by serial dilutions of DNA from S. typhi. Eighteen blood specimens from artificially infected rats and 22 blood specimens from patients were analyzed to validate the method. Considering that the most frequent Salmonella serovar isolated from blood in case of bacteremia is S. typhi, the polymerase chain reaction-microtiter plate hybridization technique could be used as a novel, rapid diagnostic method for typhoid fever, particularly when standard culture assays are negative.

Use of polymerase chain reaction and restriction enzyme analysis to directly detect and identify Salmonella typhimurium in food

A primer set of oligonucleotides (Salm 3 and Salm 4) from the invA gene of Salmonellae has been evaluated for the specific detection of Salmonella spp. by the polymerase chain reaction (PCR). This primer set amplified 33 Salmonella serovars but did not amplify 16 non-Salmonella bacteria. Moreover, after PCR amplification, it was possible to identify Salm. typhimurium by restriction enzyme analysis. The PCR-RE method developed could represent a helpful tool for detecting Salmonella spp., and for directly and rapidly identifying Salm. typhimurium in food.

Development of a PCR microplate-capture hybridization method for simple, fast and sensitive detection of Salmonella serovars in food

The authors have developed an easy and rapid detection and identification system for Salmonella spp. in food. The gene inv A was selected as the target sequence. Oligonucleotides derived from conserved regions of this gene were able to exclusively prime the amplification of a 389 bp fragment when Salmonella spp. DNA was used as the template. An internal Salmonella spp. specific DNA probe was used for confirmation of the amplified polymerase chain reaction(PCR)product, by Southern blot or microplate-capture hybridization assay. In this fashion the sensitivity of the method was increased 100-fold (4.5 fg total DNA). To validate the method, a total of 75 food samples were tested. The PCR-microplate capture hybridization assay is easy to perform and much faster than traditional detection methods for Salmonella spp. in food. Hybridization in microtitre plates is more readily observed than in Southern blot and is more sensitive than conventional agarose gel electrophoresis.

A rapid method for the identification and partial serotyping of Listeria monocytogenes in food by PCR and restriction enzyme analysis

Two highly specific primers for Listeria monocytogenes were used to yield from foods such as milk, soft cheese and meat, PCR products that were cleaved with the restriction enzyme HindIII. The fragments generated allowed a distinction between two groups of L. monocytogenes serovars: serovars 1/2a and 1/2c cluster in one group and serovars 1/2b, 3b and 4b in the other subgroup. Since this procedure can be completed in 24 h, an epidemiological association between human disease and suspected sources can be rapidly confirmed at the subgroup level in the laboratory.

p49, a putative HLA class I-specific inhibitory NK receptor belonging to the immunoglobulin superfamily

NK cells display several killer inhibitory receptors (KIR) specific for different alleles of MHC class I molecules. A family of KIR are represented by type I transmembrane proteins belonging to the immunoglobulin superfamily (Ig-SF). Besides cDNA encoding for these KIR, additional cDNA have been identified which encode for Ig-SF receptors with still undefined specificity. Here we analyze one of these cDNA, termed cl.15.212, which encodes a type I transmembrane protein characterized by two extracellular Ig-like domains and a 115-amino acid cytoplasmic tail containing a single immuno-receptor tyrosine-based inhibitory motif (ITIM) which is typical of KIR. cl.15.212 cDNA displays approximately 50 % sequence homology with other Ig-SF members. Different from the other KIR, cl.15.212 mRNA is expressed by all NK cells and by a fraction of KIR+ T cell clones. cl.15.212 cDNA codes for a membrane-bound receptor displaying an apparent molecular mass of 49 kDa, thus termed p49. To determine the specificity of the cl.15.212-encoded receptor, we generated soluble fusion proteins consisting of the ectodomain of p49 and the Fc portion of human IgG1. Soluble molecules bound efficiently to 221 cells transfected with HLA-G1, -A3, -B46 alleles and weakly to -B7 allele. On the other hand, they did not bind to 221 cells either untransfected or transfected with HLA-A2, -B51, -Cw3 or -Cw4. The binding specificity of soluble p49-Fc was confirmed by competition experiments using an anti-HLA class I-specific monoclonal antibody. Finally, different cDNA encoding for molecules homologous to cl.15.212 cDNA have been isolated, two of which lack the sequence encoding the transmembrane portion, thus suggesting they may encode soluble molecules.

The activating form of CD94 receptor complex: CD94 covalently associates with the Kp39 protein that represents the product of the NKG2-C gene

Inhibitory receptor complexes formed by CD94 and NKG2-A (Kp43) molecules have been implicated in HLA class I recognition by human natural killer (NK) cells. Additional forms of CD94 receptors have recently been described in NK cells characterized by the lack of NKG2-A expression. These CD94 receptors were shown to display activating functions. Immunoprecipitation with anti-CD94 monoclonal antibodies (mAb) led to the identification, in these cells, of a 39-kDa (Kp39) molecule that was originally believed to represent an activating isoform of the CD94 molecules. In the present study we show that the Kp39 molecule is covalently associated with CD94 and displays a protein backbone (26 kDa) similar to that of NKG2-A (Kp43) glycoproteins. Peptide mapping analysis indicates that Kp39 and NKG2-A glycoproteins belong to the same molecular family. A novel NKG2-specific mAb (termed P25) has been generated that specifically reacts with both NKG2-A and NKG2-C molecules, but fails to recognize NKG2-E molecules. Analysis of polyclonal and clonal NK cells shows that P25 mAb reacts with all NKG2-A+ cells and with a fraction of CD94+ cells lacking the expression of NKG2-A. These data indicate that NKG2-C molecules are indeed expressed only in a subset of cells lacking the expression of NKG2-A. The CD94-associated Kp39 molecule can be detected only in NKG2-A- P25+ cells, i.e. cells expressing NKG2-C molecules. Indeed, reverse transcription-polymerase chain reaction analysis performed on a large panel of NK clones indicates that NKG2-A- P25+ NK clones express the NKG2-C transcript. Notably, the cytolytic activity of these clones can be triggered by the P25 mAb in redirected killing analysis. Finally, biochemical analysis of COS7 cells cotransfected with CD94 and NKG2-C demonstrates the identity between Kp39 and NKG2-C molecules. Altogether, our data demonstrate that NKG2-C molecules associate with CD94 to form an activating receptor complex in a subset of human NK cells.

Single-strand conformation polymorphism (SSCP) analysis of Listeria monocytogenes iap gene as tool to detect different serogroups

PCR-single-strand conformation polymorphism (PCR-SSCP) analysis is a convenient technique for the detection of mutations. As the mobility of single-stranded DNA is sequence-dependent it could therefore be used to determine serotype-related sequence variations in Listeria monocytogenes. Sero-specific patterns were observed in different L. monocytogenes serogroups.

Role of amino acid position 70 in the binding affinity of p50.1 and p58.1 receptors for HLA-Cw4 molecules

In an attempt to identify the amino acid position(s) of the HLA-C-specific p58.1/p50.1 natural killer cell receptors that determine the binding affinity for their ligand, we used soluble fusion proteins formed by the ectodomain of either receptor and the Fc portion of human IgG1. We show that the soluble p50.1 (activating) receptor binds weakly to 221-Cw4 transfectants. In contrast, the soluble p58.1 (inhibitory) receptor binds with high affinity. A single amino acid mutation at position 70, obtained by site-directed mutagenesis, was found to affect the binding affinity of both the p50.1 and the p58.1 receptors. Thus, substitution in p50.1 of lysine 70 by threonine (typical of the inhibitory p58.1 molecule) resulted in a dramatic increase in binding affinity, comparable to that of the p58.1 molecule. On the other hand, substitution of threonine 70 by lysine in p58.1 almost abolished binding to 221-Cw4 cells. Our present data indicate that a single amino acid difference greatly influences the p58.1/p50.1 affinity for their HLA-C ligand and suggests a possible role of position 70 as a contact site in the natural killer cell receptor/major histocompatibility complex class I interaction.

A PCR-microplate capture hybridization method to detect Listeria monocytogenes in blood

In order to improve the diagnosis of Listeria monocytogenes infection, we have developed a polymerase chain reaction (PCR)-based assay combined with microplate capture hybridization technique. The system is based on selective amplification of L. monocytogenes with two specific primers based on the iap gene. The amplicon produced, with digoxigenin 11-dUTP incorporated during PCR, is hybridized in streptavidin-coated microtitre plates prepared with biotinylated specific DNA probe. The method involved requires approximately 6-8 h, and its high sensitivity, rapidity and simplicity should make it valuable for diagnosis and for epidemiological studies of listeriosis.