PubMed Health⌕ Search

Biomedical subjects

J Dufrenne

Publications and source records attributed to J Dufrenne.

At least 19 recordsLinked to original sources
PubMed2001

Quantification of the contamination of chicken and chicken products in the netherlands with Salmonella and Campylobacter.

The research described in this contribution provides quantitative data on contamination levels with Salmonella and Campylobacter in chicken and chicken products in The Netherlands at retail level using the most probable number method and direct counting. Most samples contained <10 Salmonella per carcass, both in fresh (89%) and frozen (68%) products, contamination levels with Campylobacter varied from <10 (18%) to more than 5,500 (18%) per fresh carcass. Most frozen samples (57%) contained < 10 Campylobacter per carcass.

Animals↗
PubMed1998

Studies on the risk assessment of Listeria monocytogenes.

Humans are frequently exposed to Listeria monocytogenes, and high numbers may be ingested during consumption of certain types of food. However, epidemiological investigations show that listeriosis is a rare disease. Risk assessment studies using an animal mouse model indicate that almost all L. monocytogenes serovars present in food have clear virulent properties. The intravenous dose causing infection in 50% (IV ID50) of mice not previously exposed to L. monocytogenes (nonprotected mice) was 1.8 log(10) units. For mice previously exposed to L.monocytogenes (immunologically protected mice was >9.0 log10 5.6 log(10) units. The ID(50) of orally exposed nonprotected mice amounted to 6.5 log10 units, and no significant effects of type of food (water/milk) and storage time at 5 degrees C (milk) were observed. The oral ID50 of immunologically protected mice was >9.0 log10 units. Furthermore, there was approximately 1-2 log10 difference between the ID50 and the lethal dose causing death in 50% (LD50). The results show that both the intestinal barrier and the specific immune defense mechanism are highly effective in preventing infection of mice orally exposed to L.monocytogenes. Delaying the immune defense had no effect on the protective activity of the intestinal barrier, indicating that these protective mechanisms independently. The risk assessment results obtained in the mouse model support the epidemiological finding that listeriosis is a rare disease in humans, despite frequent exposure to the organism.

Animals↗
PubMed1995

Characteristics of some psychrotrophic Bacillus cereus isolates.

Twelve strains of Bacillus cereus isolated from different food products and foodborne disease outbreaks, and able to grow at temperatures < 7 degrees C, were characterised. Generation times at 7 degrees C varied from 9.4 h up to 75 h. Lag phase of the vegetative cells at 7 degrees C was strongly influenced by the previous temperature history of the cells. Preincubation at 37 degrees C increased the duration of the lag phase drastically. The heat resistance at 90 degrees C (D90 degrees C-values in min) for spores produced at 30 degrees C varied from 2.2 to 9.2 min for 11 strains. One strain, however, showed a D90 degrees C-value of > 100 min. Germination of spores in milk was delayed compared to those grown in brain heart infusion broth (BHI). All strains showed production of the diarrheal type enterotoxin in BHI. Addition of 50 IU of nisin to skim milk resulted in a decrease of numbers for 9 of the 12 strains tested. At a nisin concentration of 250 IU, a decrease in bacterial numbers was observed for all strains tested.

Animals↗
PubMed1994

Characteristics of Bacillus cereus related to safe food production.

Thirty Bacillus cereus strains, isolated from different sources, were characterized in relation to safe food production. The minimal growth temperatures of the strains varied from < or = 5 degrees C to 11 degrees C. Generation times at 7 degrees C of strains capable of growing at temperatures < or = 5 degrees C were approximately 8.2 h. The D90 degrees C-values of spores of strains with a minimal growth temperature of 11 degrees C determined in phosphate buffer at pH 7.0 ranged from 4.8 to > 200 min. Strains with the capacity to grow at temperatures < or = 9 degrees C, had a D90 degrees C value ranging from 4.6 to 14 min. Addition of either nisin (250 micrograms/ml) or diacetyl (1500 micrograms/ml) to the heating menstruem at the single concentrations investigated seemed not influence the thermal destruction of spores. Germination of spores of almost all strains occurred in all three media tested (Brain Heart Infusion, rice extract and milk) even at temperatures below the minimal growth temperature. All B. cereus strains tested yielded positive results with a commercial test kit for diarrhoeal enterotoxin. The results indicate that strains with the capacity to grow at temperatures < or = 7 degrees C are not essentially different from those with minimal growth temperatures of > 10 degrees C.

Bacillus cereus↗
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

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↗
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

Phosphatidylinositol-specific phospholipase C activity as a marker to distinguish between pathogenic and nonpathogenic Listeria species.

In this study, 468 Listeria strains were checked for the presence of phosphatidylinositol-specific phospholipase C (PI-PLC) activity by using a simple assay that consisted of overlaying colonies formed on agar plates with L-alpha-phosphatidylinositol as substrate. In this assay, PI-PLC-active colonies show turbid halos around the colonies as a result of the release of insoluble diacylglycerol from the substrate. This activity was detected only in the pathogenic species Listeria monocytogenes and was not present in any of the 167 strains of Listeria seeligeri, Listeria welshimeri, Listeria innocua, Listeria murrayi, and Listeria grayi tested. Hence, screening for PI-PLC activity permits discrimination between pathogenic and nonpathogenic Listeria species. In particular, the hemolytic but nonpathogenic species L. seeligeri can now be separated from the hemolytic and pathogenic species L. monocytogenes and L. ivanovii. The use of this assay will improve the specific detection and/or isolation of pathogenic Listeria species from clinical samples or food enrichment cultures.

Base Sequence↗
PubMed1989

Specific gene probe for detection of biotyped and serotyped Listeria strains.

A total of 284 strains of Listeria, including all known serovars and biovars together with Listeria grayi and Listeria murrayi, were biotyped and serotyped. Biotyping and serotyping could be done in 2 days. A gene probe encoding a delayed hypersensitivity factor (DTH) was used in the detection of pathogenic biotypes and serotypes of the tested strains. The gene was found in all 117 tested Listeria monocytogenes strains of serogroups 1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4c, 4d, 4e, 4ab, and 7. It was also present in Listeria ivanovii. Of 78 L. monocytogenes strains of serogroup 4b, 77 strains contained the gene, whereas it was absent in all 10 tested L. monocytogenes strains of serogroup 4a. Furthermore, the gene was absent in Listeria seeligeri, L. grayi, L. murrayi, and L. innocua of serogroups 3c, 4b, and 6a and in L. welshimeri of serogroups 1/2b, 3b, 6a, and 6b. Since L. monocytogenes and L. ivanovii are the only two biotypes of the genus Listeria considered pathogens, the data obtained indicate that the DNA probe tested may be a useful tool in the detection of virulent Listeria isolates in clinical, environmental, and food samples.

Bacterial Typing Techniques↗
PubMed1988

Human serum antibodies to extracellular polysaccharides (EPS) of moulds.

The presence of antibodies to extracellular polysaccharides (EPS) of moulds in sera of healthy subjects (N = 125) was determined. Antibodies against the EPS of Penicillium digitatum, Mucor racemosus, Cladosporium cladosporioides, Fusarium moniliforme and Botrytis tulipae were found in relatively high amounts in all sera. No effect of age on antibodies present could be demonstrated. Antibodies against each of the EPS tested were only neutralized by the homologous EPS and by EPS of moulds belonging to the same genus or a taxonomically closely related genus. Antibodies against the EPS of P. digitatum were inhibited by methyl-beta-D-galactofuranoside, indicating that the galactofuranose part of this EPS is immunodominant.

Antibodies, Fungal↗
PubMed1983

Serum antibodies to enterotoxins produced by Staphylococcus aureus with special reference to enterotoxin F and toxic shock syndrome.

The presence of antibodies to staphylococcal enterotoxins (enterotoxins A through F) in sera of healthy subjects (n = 567) and in sera of patients with toxic shock syndrome (n = 20) was determined. Furthermore, production of enterotoxins by Staphylococcus aureus isolated from humans was investigated. In 46, 86, 78, 41, 20, and 91% of the sera of healthy subjects, antibodies were found against enterotoxins A, B, C, D, E, and F, respectively. The high percentage of sera with antibodies against enterotoxin F correlated with the relatively high frequency of enterotoxin F-producing S. aureus isolated from humans (one-third of the isolates produced enterotoxin F). In patients with toxic shock syndrome, antibodies against enterotoxin F were not present or were present only at very low levels. An increase of antibodies after onset of the disease was observed in two of eight patients investigated. From the results, it can be concluded that only those humans who show low levels of antibodies are susceptible to toxic shock syndrome.

Adolescent↗
PubMed1981

Persistence of Clostridium botulinum type B on a cattle farm after an outbreak of botulism.

On farms involved in botulism outbreaks, cycles of Clostridium botulinum have occurred. The cycles were initiated by feeding brewers' grains contaminated with proteolytic C. botulinum type B to the cows. Spreading of manure containing feces of these cows increased the contamination of the pastures. In grass silages prepared with wilted grass from these pastures the number of C. botulinum type B organisms increased, and toxin type B was produced. Feeding cows with the contaminated silage fodder completed the cycle. Besides contamination of human foodstuffs (milk and meat), further contamination of the environment occurred. It was demonstrated that fowl may be important vectors in spreading C. botulinum.

Animal Feed↗
PubMed1980

In vitro inactivation of Clostridium botulinum toxins types B, C and E by digestive juices of man and ducks.

Inactivation of botulinum toxins type B-L, B-M, C-L and E in the digestive juices of man and ducks was determined. Botulinum toxins of the M size (B-M and E) lost their toxicity completely in the gastric juices of both man and ducks, but toxins of the L size (B-L and C-L) lost their toxicity only partially. The toxins were hardly affected by duodenal fluid even after exposure to gastric juice. The toxins were not inactivated by cecal fluid from ducks. Since human digestive juices and those from ducks appeared to have comparable effects on the inactivation of toxin, differences in susceptibilities of the animal species to orally acquired toxins are in all probability not caused by digestive action of those species.

Animals↗
PubMed1979

[Studies on the persistence of Clostridium botulinum on a cattle farm (author's transl)].

In the winter of 1978-1979, the presence of Clostridium botulinum was studied on a cattle farm, on which botulism caused by feeding the animals contaminated brewers' grains occurred in 1977. Cl. botulinum type B, the cause of mortality among cattle at the time, was detected in grass silage prepared in 1978. This organism was not detectable in a grass silage pit dating from 1977 and made prior to the outbreak of botulism. Investigations showed that proteolytic types of C. botulinum having grass as the substrate may produce large amounts of toxin. The production of toxin in grass silage pits may, however, be prevented by a low pH in conjunction with low water activity. The present study showed that the faeces of cattle were also contaminated with Cl. botulinum type B. The degree of infection ran parallel with the degree of contamination of silage feeding in these cases.

Animal Feed↗