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S Notermans

Publications and source records attributed to S Notermans.

At least 37 records · Page 2Linked to original sources
PubMed1994

Stability of spores of Bacillus cereus stored on silicagel.

Spores of four different strains of Bacillus cereus were stored on silicagel at 22 degrees C and in physiological saline solution at -20 degrees C for a period of 260 days. At different intervals the spores were tested for survival, heat sensitivity and capacity to germinate. There was no clear change in any of the parameters tested, so storage on silicagel can be a good alternative for storage as a frozen suspension. Spores stored in this way can easily be exchanged for reference material and used for microbiological challenge testing.

Bacillus cereus↗
PubMed1994

A comparison of ELISA and RPLA for detection of Bacillus cereus diarrhoeal enterotoxin.

Fourteen strains of Bacillus cereus isolated from different sources were examined for their ability to produce diarrhoeal enterotoxin by two commercial immunoassay kits (Oxoid BCET-RPLA and Tecra ELISA) and the microslide immunodiffusion assay. One strain that was positive in monkey feedings, as well as a number of other strains isolated from diarrhoeal outbreaks, gave positive results in the ELISA and negative results in the RPLA test systems. When tested in the microslide assay, these strains produced only one antigen which formed a line of identity with the reference toxin. The results of the control toxins provided with the kits substantiated that the two commercial assays did not detect the same antigen. Cultures positive with both assay kits were shown to produce diarrhoeal enterotoxin (by a line of identity) and other antigens in the microslide immunodiffusion assay.

Antigens, Bacterial↗
PubMed1994

Resistance of bacterial strains to dry conditions: use of anhydrous silica gel in a desiccation model system.

The viability of 18 bacterial strains desiccated on anhydrous silica gel and stored at a temperature of 22 degrees C for at least 3 months was determined. According to their stability in the dried state, these strains could be classified into three typical groups. Group 1, containing Gram-positive strains and Salmonella serotypes, was marked by a very slow decrease of the concentration of culturable cells from day 14 on (respectively day 21 for Salmonella thompson). The rate of decrease expressed as regression coefficient (b) ranged from -0.000389 to -0.00521 log (cfp ml-1) per d. The Group 2 strains Enterobacter cloacae and Escherichia coli did not reach a comparable slow decrease in the dry material within the indicated time period. Regression coefficients were respectively -0.04406 and -0.03412 log (cfp ml-1) per d. The reciprocal values -(1/b) were respectively 23 d per log (cfp ml-1) and 29 d per log (cfp ml-1), indicating the time periods in which a reduction of 1 log unit of culturable cells occurred. Group 3 strains Pseudomonas aeruginosa, Aeromonas hydrophila and Aer. sobria were marked by a significant susceptibility to cell damage caused during desiccation and reconstitution. A high initial decrease (ID) of the concentration of culturable organisms seems to be a characteristic property of these bacterial strains: culturable organisms could not be detected after storage for 1 d (Aer. hydrophila, Aer. sobria) or 7 d (Ps. aeruginosa). The wide range of resistance of the different bacterial strains tested indicated that the silica gel model system is a suitable tool for microbiological challenge tests to investigate the survival of micro-organisms exposed to desiccation and their stability in dry materials.

Acclimatization↗
PubMed1994

Naturally occurring virulence-attenuated isolates of Listeria monocytogenes capable of inducing long term protection against infection by virulent strains of homologous and heterologous serotypes.

Experimental infections of mice with strains of Listeria spp. isolated from contaminated food sources allowed discrimination of strains into those either exhibiting high, attenuated or low virulence. Compared to the highly virulent L. monocytogenes strain EGD, an attenuated strain such as L99 persisted for shorter times (5 versus 10 days) in the infected host. Using a tissue culture cell model of infection, we found that, although strain L99 was capable of accumulating actin like its virulent counterpart following invasion, it was unable to generate the polarized actin tails required for intracellular and cell-to-cell movement. Immunoblot analysis using specific antiserum to the ActA polypeptide, a molecule that is necessary for movement of the bacterium within the eucaryotic cell, indicated that a slightly truncated form of this polypeptide was produced in the L99 strain. Despite its reduced virulence, the attenuated strain L99 was just as effective in generating protection in immune mice as the highly virulent strains, albeit with a 1000-fold higher infective dose. Based on the results obtained from this study, we suggest that one of the mechanisms accounting for widespread resistance in humans to infection by Listeria may be due to asymptomatic infections by naturally occurring strains attenuated for virulence.

Animals↗
PubMed1993

Immuno-assay techniques for detecting yeasts in foods.

A brief literature review on immuno-assay of yeast cell wall antigens is given. Special attention is paid to extracellular, thermostable yeast antigens (EPS), which are released to the growth medium by many yeast species. The EPS of Saccharomyces cerevisiae and of Stephanoascus ciferrii (syn. Candida ciferrii) could be specifically and sensitively detected by a sandwich ELISA, using an IgG raised in rabbits immunized with the EPS of these yeasts. The EPS ELISA of three basidiomycetous yeasts tested was not specific, that of Geotrichum candidum was genus-specific but was not sensitive. The EPS of Zygosaccharomyces bailii could be detected in a highly specific competitive ELISA but not in a sandwich ELISA or in a latex agglutination test.

Antigens, Fungal↗
PubMed1993

Cost-benefit analysis of a screening strategy for Salmonella enteritidis in poultry.

Salmonella enteritidis is an emerging problem in several industrial countries. Outbreaks caused by this organism are almost always associated with the consumption of eggs and egg-products originating from infected poultry flocks. To reduce human infection, elimination of contaminated flocks could be considered. In this study we estimated the effectiveness of such a measure to reduce human infections. If poultry flocks are screened for S. enteritidis only once during their laying period, there is a 43.7% reduction in contaminated eggs. The effectiveness increases if the frequency of screening is increased, resulting in a 65.4% reduction in contaminated eggs after three screenings. The costs of this intervention strategy are determined by both the costs of screening and the economic losses of destroying poultry flocks.

Animals↗
PubMed1992

Mycological condition of maize products.

Maize and maize-related products were investigated in a collaborative study for viable moulds and antigenic extracellular polysaccharides (EPS) produced by Aspergillus and Penicillium species. In addition, the samples were tested for the presence of aflatoxin B1. All maize products, with the exception of the heat processed products, contained viable moulds on an average of (log10 values) 3.3 +/- 0.7 colony-forming units per gram. In most samples a mixed mould flora was present. Species of the genus Fusarium were dominant, followed by Aspergillus, Eurotium and Penicillium. The mould colony count correlated positively with the presence of antigenic extracellular polysaccharides produced by species of Aspergillus and Penicillium. Gamma irradiation did not affect the detection of antigenic extracellular polysaccharides. Aflatoxin B1 was detected in two out of 35 samples; these contained 0.6 and 0.8 microgram/kg. From one of these aflatoxin B1-containing samples, Aspergillus flavus was isolated.

Aflatoxin B1↗
PubMed1992

A comparative study of randomly amplified polymorphic DNA analysis and conventional phage typing for epidemiological studies of Listeria monocytogenes isolates.

The analysis of RAPD profiles generated by PCR with a single 10-mer, HLWL74, was compared to bacteriophage susceptibility data for epidemiological typing of Listeria monocytogenes strains. A total of 104 L. monocytogenes strains was screened, all from serogroup 1 or serotype 4b. Of these, 53 had been isolated during 6 different listeriosis outbreaks. The remaining 51 strains were chosen randomly from our collection. A total of 38 RAPD types were observed, although each epidemic group of strains isolated during one of these outbreaks displayed a specific RAPD profile. For 98% of the strains isolated during outbreaks, the correlation between RAPD typing and phage typing was complete. Only one strain, typed as epidemic by phage typing, was clearly distinguishable from the others by RAPD analysis. Among the 51 strains not related to an outbreak, 12 were linked to epidemic groups by RAPD analysis. Two of these rearrangements were supported by phage typing. The remaining 10 strains could be excluded by phage typing from any of the epidemic groups studies. Considering all 104 isolates, the decision to relate a strain to a particular epidemic group or to exclude a strain from any epidemic group was the same for 92 isolates, using either phage typing or RAPD analysis. The RAPD analysis, which is quick, simple and suited for automation, is proposed as an attractive alternative for phage typing in epidemiological studies of listeriosis.

Bacterial Typing Techniques↗
PubMed1992

Suitability of the prfA gene, which encodes a regulator of virulence genes in Listeria monocytogenes, in the identification of pathogenic Listeria spp.

The pathogenesis of listerial infections is complex and involves a number of virulence factors expressed by virulent Listeria species. We have recently described a regulator gene, prfA, that positively regulates the expression of a number of virulence factors in Listeria monocytogenes. When the prfA gene was used as a DNA probe, we found it to be extremely specific for the pathogenic species L. monocytogenes. No reaction was obtained with strains of all other species of this genus. By using this information, an oligonucleotide primer pair was developed that specifically amplifies the prfA gene in L. monocytogenes strains of all known serotypes.

Base Sequence↗
PubMed1992

Coordinate regulation of virulence genes in Listeria monocytogenes requires the product of the prfA gene.

The prfA gene of Listeria monocytogenes encodes a protein that activates transcription of the listeriolysin gene (lisA). In order to explore the role of the prfA gene product in the pathogenesis of listerial infection, we constructed a site-directed insertion mutation in prfA by the chromosomal integration of a novel suicide vector containing a portion of the prfA coding region. This mutation not only transcriptionally silenced the listeriolysin (lisA) gene but also abrogated production of specific RNA transcripts corresponding to the phosphatidylinositol-specific phospholipase C (pic) and metalloprotease (mpl) genes, two further virulence gene products expressed only by pathogenic Listeria strains. The strain was also found to be avirulent when tested in a mouse model of listerial infection. The concomitant loss of multiple characteristics such as production of LisA, Pic, Mpl, and loss of virulence in a mouse infection model is the result of a mutation in a single gene and demonstrates that the prfA gene product is a positive regulator of multiple virulence determinants in L. monocytogenes.

Animals↗
PubMed1991

Immunological methods for detection of foodborne pathogens and their toxins.

Improved methods to detect microorganisms and their toxins introduced during the last decade involve among others recombinant DNA techniques and various immuno-assays such as the enzyme-linked immunosorbent assay and the latex agglutination. Immuno-assays are based on a quantitative reaction of an antigen (bacterial metabolite, e.g., toxin) with its antibody. Therefore, they are suited for detection of microorganisms based on their production of specific antigens and for quantitative detection of bacterial toxins. Sensitivity and specificity of immuno-assays are mainly determined by the antiserum used. In this respect the use of well selected monoclonal antibodies can be of advantage. With the enzyme-linked immunosorbent assay and latex agglutination test quantities of 0.1-1 ng of antigen/ml can be detected. Of both techniques the latex agglutination method has several advantages; the method is simple, inexpensive and rapid. Since each immuno-assay is sensitive to non-specific reactions, recognition of false positive results is necessary. The most appropriate method for this is to add an inhibitor to the test sample which blocks specifically the paratope of the immunoglobulin. Another general disadvantage of immuno-assays is that only the antigenicity is determined and this may differ from the actual toxicity. Therefore, antibodies should be used that react with the toxic centre(s) of the molecule, which can be accomplished by using well selected monoclonal antibodies.

Animals↗
PubMed1991

Feasibility of a reference material for staphylococcal enterotoxin A.

A reference material for staphylococcal enterotoxin A (SEA), was produced by spray-drying the toxin in milk. With this procedure the SEA was distributed homogeneously in the material. For ease of handling the reference material was encased in gelatin capsules, each containing 405 ng of SEA. Simply dissolving the milk powder in distilled water resulted in a 100% recovery of the SEA present. The reference material would appear suitable for testing laboratory performance, comparison of detection methods and to validation of extraction procedures.

Aerosols↗
PubMed1991

DNA hybridization and latex agglutination for detection of heat-labile- and shiga-like toxin-producing Escherichia coli in meat.

DNA-hybridization and latex-agglutination tests were used for screening of a group of Escherichia coli isolates for heat-labile enterotoxin (LT)- and shiga-like toxin (SLT1 or VT1) -producing strains, respectively. Strains tested originated from 162 meat samples (poultry, pigs and beef) chosen at random. Additionally LT- and SLT1-producing reference strains were tested. The DNA-hybridization technique allowed screening of large numbers of strains, whereas large scale testing of strains by latex agglutination was laborious. Of 800 E. coli strains tested by DNA hybridization none contained the gene encoding LT. Production of LT as tested by latex agglutination was not found. The gene encoding SLT1 was detected in 10 of the 800 isolates tested. None of these strains, however, showed cytotoxicity on Vero cells. Serotyping was done with sorbitol-negative E. coli strains, first by using the latex-agglutination test for O157 followed by complete serotyping. No E. coli of serogroup O157 were found. Therefore the results obtained also indicate that routine screening of E. coli isolated randomly from food for toxin production is not useful and should be limited to food-borne disease outbreaks with an etiology resembling an E. coli infection.

Animals↗
PubMed1991

Adaptation of Listeria in liquid egg containing sucrose resulting in survival and outgrowth.

Survival of Listeria species was tested in liquid egg products such as albumen, yolk, whole egg and whole egg containing 25% sucrose. At an incubation temperature of 4 degrees C Listeria survived in all products, and even increased slightly in yolk, whole egg and whole egg containing 25% sucrose. However, at 20-22 degrees C, in whole egg containing sucrose, a rapid an dramatic decrease in numbers of Listeria was observed. Following this initial decrease, an increase in the numbers of Listeria was observed. The ability to grow in liquid egg containing sucrose was maintained upon reinoculation into a freshly prepared product. However, this property disappeared after subculturing in brain heart infusion broth. The significance of these findings is discussed.

Animals↗
PubMed1991

Successful approach for detection of low numbers of enterotoxigenic Escherichia coli in minced meat by using the polymerase chain reaction.

The polymerase chain reaction (PCR) was used as a tool for the detection of enterotoxigenic Escherichia coli in minced meat. With two synthetic 29-mer oligonucleotides, a 195-bp fragment from the E. coli heat-labile enterotoxin (LT) gene could be amplified specifically. When 6 CFU was added to the reaction mixture as a template, the PCR yielded sufficient amplified product for visualization on an agarose gel. Prior to PCR amplification, the minced meat samples were subjected to enrichment culturing for E. coli. From these cultures, 10 microliters was used in the PCR assay. All 20 25-g samples that were examined in this assay were negative for E. coli LT. However, when 3 CFU of E. coli LT was added to the 25-g samples of minced meat prior to enrichment culturing, the PCR assay yielded positive results.

Bacterial Toxins↗
PubMed1990

Testing strains of Clostridium perfringens type A isolated from diarrhoeic piglets for the presence of the enterotoxin gene.

A diarrhoeic syndrome in piglets has been linked to Clostridium perfringens type A because this organism has been isolated in large numbers from all cases. The strains isolated from these cases and strains isolated from healthy piglets were screened for the enterotoxin gene of C perfringens by DNA-hybridisation. Using two different synthetic DNA-probes, none of the strains isolated from diseased pigs was positive in this reaction, indicating that the enterotoxin of C perfringens is not involved in the syndrome.

Animals↗
PubMed1990

Inactivation of staphylococcal enterotoxins by heat and reactivation by high pH treatment.

Inactivation of staphylococcal enterotoxins (SE) added to different media upon heat treatment (80 degrees C or 100 degrees C for 10 min) and reactivation of inactivated SE was studied. In gelatin (pH 4.0), lettuce extract, peas and beans extracts and ovalbumin (pH 5.0) the immunological activity of SE was lost almost completely upon heating. The loss of immunological activity of SEA was accompanied by a concomitant loss of biological activity of this toxin (monkey feeding test). A high pH treatment (pH 11) of the different preparations restored both the immunological and biological activity in most samples tested. Heating at 80 degrees C or 100 degrees C for 10 min of SE containing gelatin (pH 7.0), cauliflower extract (pH 4.0 or pH 7.0), milk (pH 4.0), casein (pH 6.0), rice extract (pH 7.0), noodles extract (pH 4.0) and oat-flakes extract (pH 7.0) had a much lower effect on the immunological activity of the SE (activity greater than or equal to 25%).

Animals↗