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Biomedical subjects

F M van Leusden

Publications and source records attributed to F M van Leusden.

At least 19 recordsLinked to original sources
PubMed2006

Spores from mesophilic Bacillus cereus strains germinate better and grow faster in simulated gastro-intestinal conditions than spores from psychrotrophic strains.

The species Bacillus cereus, known for its ability to cause food borne disease, consists of a large variety of strains. An important property for discrimination of strains is their growth temperature range. Psychrotrophic strains can grow well at refrigerator temperatures but grow at 37 degrees C with difficulty. Mesophilic strains on the other hand are unable to grow below 10 degrees C, but grow well at 37 degrees C. Spores of six psychrotrophic and six mesophilic strains were investigated for their ability to survive and grow in simulated gastro-intestinal fluids, mimicking the conditions in the gastro-intestinal tract. The germination potential of psychrotrophic and mesophilic spores in simulated intestinal fluid does not differ much. Under conditions simulating the gastro-intestinal passage, 5 out of 6 mesophilic strains showed growth, and only 2 out of 6 psychrotrophic strains. Temperature (37 degrees C) and simulated gastro-intestinal conditions together influenced germination and growth.

Bacillus cereus↗
PubMed2006

Prevalence of potentially pathogenic Bacillus cereus in food commodities in The Netherlands.

Randomly selected food commodities, categorized in product groups, were investigated for the presence and number of Bacillus cereus bacteria. If positive, and when possible, five separate colonies were isolated and investigated for the presence of four virulence factors: presence of genes encoding three enterotoxins (hemolysin BL [HBL], nonhemolytic enterotoxin [NHE], and cytotoxin K) and the ability to produce cereulide. In addition, the presence of psychrotrophic and mesophilic signatures was determined. The genes for NHE are found in more than 97% of the isolates, those for HBL in approximately 66% of the isolates, and the gene for cytotoxin K in nearly 50% of the isolates. Significant associations between product groups and (combinations of) virulence factors were the relatively low percentage of isolates from the "flavorings" group containing genes encoding NHE and the higher-than-average occurrence of both the genes encoding HBL and NHE in the "pastry" group. Cereulide was produced by 8.2% of the isolates but only in combination with the presence of genes for one or more other virulence factors. Most isolates (89.9%) were mesophilic; minorities of the isolates were psychrotrophic (4.4%) or of intermediate signature (5.7%). In the product group "milk and milk products," the incidence of strains with psychrotrophic or intermediate signatures is significantly higher than in the other product groups. In the product groups "flavorings," "milk and milk products," "vegetable(s) and vegetable products," "pastry," and "ready-to-eat foods," a relatively high number of samples contain high numbers of B. cereus bacteria. Within the product group "ready-to-eat foods," the products containing rice and pasta show a relatively high incidence of high numbers of B. cereus bacteria.

Animals↗
PubMed2003

The adaptive response of Escherichia coli O157 in an environment with changing pH.

AIMS: To predict and validate survival of non-acid adapted Escherichia coli O157 in an environment mimicking the human stomach. METHODS AND RESULTS: Survival was predicted mathematically from inactivation rates at various, but constant pH values. Predictions were subsequently validated experimentally in a pH-controlled fermentor. Contrary to prediction, acid-sensitive cultures of E. coli O157 survived for a long period of time and died as rapidly as acid-resistant cultures. Experimental results showed that in an environment with changing pH, acid-sensitive cultures became acid-resistant within 17 min. Cyclo fatty acids was reported to be a factor in acid resistance. As synthesis of cyclo fatty acids does not require de novo enzyme synthesis and thus requires little time to develop, we analysed the membrane fatty acid composition of E. coli O157 during adaptation. No changes in membrane fatty acid composition were observed. CONCLUSIONS: Acid adaptation of E. coli O157 can occur during passage of the human gastric acid barrier, which can take up to 4 h. SIGNIFICANCE AND IMPACT OF THE STUDY: The ability of acid-adapted bacteria to survive the human stomach is an important virulence factor. The ability of non-acid adapted E. coli O157 to adapt within a very short period of time under extreme conditions further contributes to the virulence of E. coli O157.

Adaptation, Physiological↗
PubMed2003

Adaptive responses of Salmonella enterica serovar Typhimurium DT104 and other S. Typhimurium strains and Escherichia coli O157 to low pH environments.

AIMS: Cattle are a known main reservoir for acid-resistant Escherichia coli O157 and Salmonella enterica serovar Typhimurium DT104. We studied the response of S. Typhimurium DT104 to extreme low pH environments and compared their response to that of acid-resistant E. coli O157 and other S. Typhimurium phage types. METHODS AND RESULTS: Bacteria were grown in nutrient-rich medium and subsequently acid challenged at pH 2.5. We found that stationary phase cultures of various S. Typhimurium strains were able to survive a challenge for 2 h at pH 2.5. As in E. coli, the ability of S. Typhimurium to survive at pH 2.5 was shown to be dependent on the presence of amino acids, specifically arginine. The amount of proton pumping H+/ATPase, both in E. coli O157 and S. Typhimurium strains, was lower when grown at pH values <6 than after growth at pH 7.5. Cyclo fatty acid content of membranes of bacteria grown at pH values <6 was higher than that of membranes of bacteria grown at pH 7.5. CONCLUSIONS: Various S. Typhimurium strains, both DT104 and non-DT104, are able to survive for a prolonged period of time at pH 2.5. Their response to such low pH environment is seemingly similar to that of E. coli O157. SIGNIFICANCE AND IMPACT OF THE STUDY: Food-borne pathogens like S. Typhimurium DT104 and E. coli O157 form a serious threat to public health since such strains are able to survive under extreme low pH conditions as present in the human stomach. The emergence these acid-resistant strains suggests the presence of a selection barrier. The intestinal tract of ruminants fed a carbohydrate-rich diet might be such a barrier.

Adaptation, Physiological↗
PubMed2001

Detection of genes encoding for enterotoxins and determination of the production of enterotoxins by HBL blood plates and immunoassays of psychrotrophic strains of Bacillus cereus isolated from pasteurised milk.

The presence of genes for the production of the three components of the HBL enterotoxin complex and enterotoxin-T in Bacillus cereus was evaluated by PCR tests for strains isolated from milk. In addition enterotoxin production of B. cereus was evaluated by means of the HBL blood agar plate and two commercially available toxin tests. All three genes for the HBL enterotoxin complex were detected in 55% of the 86 strains tested, the enterotoxin-T gene was detected in 62% of the strains. A few strains showed a weak reaction in the PCR tests for the L1 or L2 components of the HBL enterotoxin complex. Many strains that were found to contain the genes for the HBL complex gave negative or doubtful results in the HBL blood agar plate test. All strains that contain the L2 part of the HBL complex showed a titer of at least 8 in the Oxoid RPLA test. Two strains that did not contain the L2 part of the HBL enterotoxin complex gave high titers (= 64) in the RPLA test.

Animals↗
PubMed2001

A rat model for dose-response relationships of Salmonella Enteritidis infection.

AIMS: To develop an animal model to study dose-response relationships of enteropathogenic bacteria. METHODS AND RESULTS: Adult, male Wistar Unilever rats were exposed orally to different doses of Salmonella enterica serovar Enteritidis after overnight starvation and neutralization of gastric acid by sodium bicarbonate. The spleen was the most sensitive and reproducible organ for detection of dose-dependent systemic infection. Illness was only observed in animals exposed to doses of 10(8) cfu or more. At lower doses, histopathological changes in the gastro-intestinal tract were observed, but these were not accompanied by illness. Marked changes in numbers and types of white blood cells, as well as delayed-type hyperresponsiveness, indicated a strong, dose-dependent cellular immune response to Salm. Enteritidis. CONCLUSION: The rat model is a sensitive and reproducible tool for studying the effects of oral exposure to Salm. Enteritidis over a wide dose range. SIGNIFICANCE AND IMPACT OF THE STUDY: The rat model allows controlled quantification of different factors related to the host, pathogen and food matrix on initial stages of infection by food-borne bacterial pathogens.

Administration, Oral↗
PubMed2000

Marker antigens to assess exposure to molds and their allergens. I. Aspergillus fumigatus.

BACKGROUND: Exposure to molds and mold products in the indoor environment may lead to allergies, asthma, or respiratory complaints in general. Enumeration of viable parts of molds in the environment is insufficient to estimate exposure. Therefore, other methods have to be developed. METHODS: Aspergillus fumigatus (Af) was grown under various circumstances (22 degrees C and 30 degrees C, high and low water activity) in the laboratory. At various moments during culture, extracts were taken, and antigen and allergen content was examined by acrylamide electrophoresis and immunoblot. RESULTS: In extracts of the culture filtrate, two antigens were found to be produced under all studied growth conditions (common antigens). In the extracts of the water-soluble portion of the mycelium, one common antigen was found. CONCLUSIONS: The three common antigens may serve as marker antigens for exposure to Af and its products. In view of the simultaneous presence of two of these common antigens with Af allergens, these two marker antigens may be used to estimate exposure to allergens of Af.

Air Pollution, Indoor↗
PubMed2000

Marker antigens to assess exposure to molds and their allergens. II. Alternaria alternata.

The estimation of exposure to molds and their products in the indoor environment, which may lead to the occurrence of allergies or respiratory complaints, by means of enumeration of viable parts is inadequate. Therefore, other methods must be developed. When grown under various circumstances (22 degrees C and 30 degrees C, high and low water activity) under laboratory conditions, Alternaria alternata produces one antigen that can be found under all studied growth conditions in extracts of the water-soluble portion of the mycelium. This common antigen may serve as marker antigen for exposure to A. alternata and its allergens. In extracts of the culture filtrate, three antigens, designated index antigens, have been identified that together may have the function of marker for the exposure to allergens of A. alternata.

Air Pollution, Indoor↗
PubMed1987

[Reconsideration of the 'bacteriological examination' of slaughter stock].

A comparative trial was made by six meat inspection services to attain uniform indications for the 'Bacteriological Examination' of slaughtered animals in accordance with the 'Meat Inspection Regulations' of the Dutch 'Meat Inspection Act'. The results of the study compelled the investigators to scrutinize these regulations. The 'Bacteriological Examination' which is prescribed, is designed to exclude septicaemic animals from human consumption. Applying the rules will result in condemnation of animals harbouring a small number of bacteria which have a minimum significance for the health of consumers, whereas animals harbouring organisms potentially pathogenic for man are overlooked. It is concluded that the 'Meat Inspection Regulations' should be considered.

Animals↗
PubMed1986

[More than 10 years of kidney testing in the Netherlands, and now...?].

A historical review of testing for antibacterial residues in slaughtered animals is presented. In recent developments, much attention was paid to microbiological methods. Because of changing views and new possibilities increasing attention is being paid to purely chemical methods of detection. However, so long as chemical multi-purpose methods are not available, there will be a need for microbiological methods. The common misunderstanding that prevention of residues of antibacterial compounds in slaughter animals will contribute to reduction of the problem of bacterial resistance to antibacterial agents, is warned against.

Animals↗
PubMed1985

Collaborative study on the isolation of salmonella from artificially contaminated milk powder.

The suitability of artificially contaminated milk powder as a substrate for salmonella reference samples and its stability under different storage conditions were studied. The need for a reconstitution step in the standard isolation method for salmonellas from milk powders was also investigated. When milk powder was examined in this way with a reconstitution step, differences in laboratory methods and/or storage times had no significant effect on the results after storage at 4 degrees C. With powder stored at room temperature there was a systematic decrease in the number of samples positive as the storage time increased. It is concluded therefore that milk powder contaminated with salmonellas should be stored at 4 degrees C. Examination of such milk powder with a reconstitution step yielded better results than without it and this step is therefore necessary for improving the reproducibility of the method. No significant differences were encountered between the standard isolation method and that used in the authors' laboratories. The results of this study indicate that milk powder is suitable as basic material for reference samples and that a reconstitution step should be included in the standard salmonella isolation procedure.

Animals↗
PubMed1985

Reference material for the evaluation of a standard method for the detection of salmonellas in foods and feeding stuffs.

To evaluate a standard salmonella isolation method a reference material consisting of 0.2 g spray-dried milk inoculated with Salmonella typhimurium and contained in gelatin capsules was prepared. The organisms were distributed homogeneously between capsules, and their numbers were stable for 120 d when the capsules were stored in dry conditions at 4 degrees C. Addition of these capsules with or without food samples to pre-enrichment broth gave low and reproducible levels of Salm. typhimurium contamination without altering the pre-enrichment and without influencing the other bacterial flora present. As a result of an interlaboratory trial, the reference material indicated that the food and/or its competitive flora may have a negative influence on the detection of salmonellas.

Animals↗
PubMed1984

[Detection of antibiotics and/or chemotherapeutic agents in slaughtering pigs by a captive impedance measurement using the M 120 Bactometer].

A study was performed to compare the use of capacitive impedance measurement with EEC 4-plate method for the detection of antibacterial residues. Urine, meat, kidney and spleen were the matrices used in the impedance measurement. Meat was used in the EEC 4-plate method. Capacitive impedance measurement is quick, relatively simple, and reliable method, in which objective interpretation of the test results is guaranteed by automatic apparatus. Using meat and kidney as matrices, the test appears to be an efficient screening test for export meat and edible offal. As far as domestic Meat Inspection legislation is concerned, the test described may provide more specific information than the methods presently in use.

Animals↗
PubMed1984

Evaluation of a pour-plate system with a rabbit plasma-bovine fibrinogen agar for the enumeration of Staphylococcus aureus in food.

Investigations were carried out concerning the selectivity and productivity of rabbit plasma fibrinogen (RPF) agar according to Beckers et al. (H. J. Beckers, F. M. van Leusden, W. M. Hogeboom, and E. H. M. Delfgou-van Asch. 1980. De Ware(n)-Chemicus, 10: 125-130). Its selectivity was compared with pork plasma fibrinogen (PPF) medium according to Hauschild et al. (A. H. W. Hauschild, C. E. Park, and R. Hilsheimer. 1979. Can. J. Microbiol. 25: 1052-1057) and its productivity was compared with PPF medium and Baird-Parker's egg yolk tellurite glycine pyruvate (ETGP) agar. In total 139 samples of naturally contaminated foodstuffs were examined. RPF agar scored higher than ETGP agar; although only small (mean value of differences 0.09 log units), the differences were statistically significant. While no significant differences in sensitivity between RPF agar and PPF medium were encountered, RPF agar was statistically more selective than PPF medium. It is concluded that RPF agar is very suitable for the enumeration of Staphyloccus aureus in foods.

Agar↗
PubMed1980

Laboratory induced variations in a standardized Salmonella isolation method.

Four microbiologists from four European laboratories came together to a single laboratory for two weeks and during that period examined 100 samples of minced meat artificially contaminated with salmonellae and 100 naturally contaminated samples using a standardized technique. No significant differences were found between the results obtained by the different analysts with 92 to 97 of the artificially contaminated and 30 to 42 of the naturally contaminated samples being found positive. Over a further period of eight weeks, these analysts examined the same number of samples in their own laboratories again using an identical procedure. There were no significant containing approximately 100 salmonellae per gram but significant differences (43 to 93) were found in isolation rates from the artificially contaminated samples copntaining approximately 1 salmonella per gram. The differences in findings between the first and the second part of the experiments may have been caused fairly by variations in media preparation, temperature of incubators, storage conditions of media and thawing conditions of samples etc., and secondly by differences in working conditions such as performing only one task during two weeks in contrast to examining the samples as part of the daily routine. At high levels of contamination, these factors do not appear to have an important influence on the performance of a laboratory.

Animals↗
PubMed1980

Epidemiological studies on Salmonella in a certain area ("Walcheren Project"). IV. The incidence of Salmonella in the sewage system, in the faeces of man and pets as well as in shops, kitchens and lavatories in the village of Aagtekerke.

As part of the epidemiological investigations on Salmonella ion the former island of Walcheren, the contamination of sewage water in the village of Aagtekerke was studied over a prolonged period of time. These studies showed that this sewage water was frequently contaminated by large numbers of Salmonella. In the present study efforts were made to find the source of this contamination and for this purpose the incidence of Salmonella in the sewage system, in the faeces of man and pets as well as in shops, kitchens and lavatories in the village of Aagtekerke was studied for a period of three weeks in June 1977. Salmonella was only isolated from a few samples of faecal material of human and animal origin, and from the sewage system (including the inlet water and effluents of the sewage works). Serotyping showed that the strains isolated from human faeces were similar to those found to be present in the sewage system. This fact taken in conjunction with the results of the bacterial counts, suggests that the sewage system was only contaminated by a small number of carriers. The reduction of contamination observed in the sewage system during the period of investigation could be evidence that Salmonella organisms cannot survive by themselves in an environment of this type, at least not at the temperatures recorded when collecting samples from the sewage water. Growth of organisms under more favourable conditions cannot be ruled out. A questionnaire about the dietary habits and kitchen hygiene of the local population showed that contamination within households, originating with the food, is a real possibility.

Adult↗