Biomedical subjects

R R Beumer

Publications and source records attributed to R R Beumer.

At least 19 recordsLinked to original sources

PubMed2004

Behavior of Clostridium perfringens at low temperatures.

Refrigerated storage is an important step in the preparation of foods and inadequate storage is one of the main causes of food poisoning outbreaks of Clostridium perfringens. Therefore, growth and germination characteristics of C. perfringens in a temperature range of 3-42 degrees C were determined in fluid thioglycollate broth (FTG) and Dutch pea soup. To study the effect of adaptation, cells were either inoculated from a 37 degrees C pre-culture or from a temperature-adapted pre-culture. Membrane fatty acid patterns were determined at all temperatures to examine the effect of temperature on membrane composition. Spores were either inoculated with and without heat treatment. Adaptation of cells did not influence growth rate nor lag phase. Growth in pea soup, however, was slower and lag phases tended to be more extended compared to FTG. No growth was observed at temperatures < or =10 degrees C and death rates in pea soup were higher than those in FTG at these low temperatures. Cells preserved the membrane fluidity by reducing the arachidic acid content and increasing the lauric acid content when the temperature dropped. This resulted in a net reduction in chain length. Microscopic analysis of cells grown at 15 degrees C revealed a morphological change: cells were elongated compared to those grown at 37 degrees C. These data demonstrate the ability of C. perfringens to adapt to lower temperatures. However, this did not influence growth characteristics compared to non-adapted cells. Spores of C. perfringens did germinate at all temperatures with and without heat-activation. Combining this fact with the extended survival at low temperatures emphasizes the need for adequate heating of refrigerated foods before consumption to eliminate health risks due to C. perfringens.

Adaptation, Physiological↗

PubMed2004

Effect of cooling on Clostridium perfringens in pea soup.

Foods associated with Clostridium perfringens outbreaks are usually abused after cooking. Because of their short generation times, C. perfringens spores and cells can grow out to high levels during improper cooling. Therefore, the potential of C. perfringens to multiply in Dutch pea soup during different cooling times was investigated. Tubes of preheated pea soup (50 degrees C) were inoculated with cocktails of cells or heat-activated spores of this pathogen. The tubes were linearly cooled to 15 degrees C in time spans of 3, 5, 7.5, and 10 h and were subsequently stored in a refrigerator at 3 or 7 degrees C for up to 84 h. Cell numbers increased by 1-log cycle during the 3-h cooling period and reached their maximum after 10 h of cooling. Subsequent refrigeration hardly reduced cell numbers. Cooling of 3.75 liters of pea soup in an open pan showed that this amount of pea soup cooled from 50 to 15 degrees C in 5 h, which will allow a more than 10-fold increase in cell numbers. These findings emphasize the need of good hygienic practices and quick cooling of heated foods after preparation.

Clostridium perfringens↗

PubMed2004

A new protocol for the detection of Enterobacter sakazakii applied to environmental samples.

Enterobacter sakazakii is a motile, peritrichous, gram-negative rod that was previously known as a yellow pigmented Enterobacter cloacae. It is documented as a rare cause of outbreaks and sporadic cases of life-threatening neonatal meningitis, necrotizing enterocolitis, and sepsis. E. sakazakii has been isolated from milk powder-based formulas, and there is thus a need to investigate whether and where E. sakazakii occurs in these manufacturing environments. For this purpose, a simple detection method was developed based on two features of E. sakazakii: its yellow pigmented colonies when grown on tryptone soy agar and its constitutive alpha-glucosidase, which is detected in a 4-h colorimetric assay. Using this screening method, E. sakazakii strains were isolated from three individual factories from 18 of 152 environmental samples, such as scrapings from dust, vacuum cleaner bags, and spilled product near equipment. The method is useful for routine screening of environmental samples for the presence of E. sakazakii.

Colorimetry↗

PubMed2004

A quantitative analysis of cross-contamination of Salmonella and Campylobacter spp. via domestic kitchen surfaces.

Epidemiological data indicate that cross-contamination during food preparation in the home contributes noticeably to the occurrence of foodborne diseases. To help prevent such occurrences, the inclusion of a cross-contamination model in exposure assessments would aid in the development and evaluation of interventions used to control the spread of pathogenic bacteria. A quantitative analysis was carried out to estimate the probability of contamination and the levels of Salmonella and Campylobacter spp. on salads as a result of cross-contamination from contaminated chicken carcasses via kitchen surfaces. Data on the prevalence and numbers of these bacteria on retail chicken carcasses and the use of unwashed surfaces to prepare foods were collected from scientific literature. The rates of bacterial transfer were collected from laboratory experiments and literature. A deterministic approach and Monte Carlo simulations that incorporated input parameter distributions were used to estimate the contamination of the product. The results have shown that the probability of Campylobacter spp. contamination on salads is higher than that of Salmonella spp., since both the prevalence and levels of Campylobacter spp. on chicken carcasses are higher than those of Salmonella spp. It is realistic to expect that a fraction of the human exposure to Campylobacter spp., in particular, originates from cross-contamination in private kitchens during food handling. The number of human campylobacteriosis cases could be reduced either by reducing the degree of Campylobacter spp. contamination on chicken carcasses or by improving the hygiene in private kitchens. To eliminate the cross-contamination route, it is important to use separate surfaces or to properly wash the surfaces during the preparation of raw and cooked foods or ready-to-eat foods.

Animals↗

PubMed2003

Survival of foodborne pathogens on stainless steel surfaces and cross-contamination to foods.

The retention of bacteria on food contact surfaces increases the risk of cross-contamination of these microorganisms to food. The risk has been considered to be lowered when the surfaces are dry, partly because bacterial growth and survival would be reduced. However, some non-spore-forming bacteria might be able to withstand dry conditions on surfaces for an extensive period of time. In this study the survival of Salmonella enteritidis, Staphylococcus aureus and Campylobacter jejuni on stainless steel surfaces at different initial levels was determined at room temperature. The transfer rates of these pathogens from kitchen sponges to stainless steel surfaces and from these surfaces to foods were also investigated. Staph. aureus was recovered from the surfaces for at least 4 days when the contamination level was high (10(5) CFU/cm2) or moderate (10(3) CFU/cm2). At low levels (10 CFU/cm2), the surviving numbers decreased below the detection limit (4 CFU/100 cm2) within 2 days. S. enteritidis was recovered from surfaces for at least 4 days at high contamination levels, but at moderate level, the numbers decreased to the detection limit within 24 h and at low level within 1 h. C. jejuni was the most susceptible to slow-air-drying on surfaces; at high contamination levels, the numbers decreased below the detection limit within 4 h. The test microorganisms were readily transmitted from the wet sponges to the stainless steel surfaces and from these surfaces to the cucumber and chicken fillet slices, with the transfer rates varied from 20% to 100%. This study has highlighted the fact that pathogens remain viable on dry stainless steel surfaces and present a contamination hazard for considerable periods of time, dependent on the contamination levels and type of pathogen. Systematic studies on the risks of pathogen transfer associated with surface cleaning using contaminated sponges provide quantitative data from which a model of risks assessment in domestic setting could lead.

Bacterial Adhesion↗

PubMed2003

Comparison of media for enumeration of Clostridium perfringens from foods.

Many media have been developed to enumerate Clostridium perfringens from foods. In this study, six media [iron sulfite (IS) agar, tryptose sulfite cycloserine (TSC) agar, Shahidi Ferguson perfringens (SFP) agar, sulfite cycloserine azide (SCA), differential clostridial agar (DCA), and oleandomycin polymyxin sulfadiazine perfringens (OPSP) agar] were compared in a prestudy, of which four (IS, TSC, SCA, and DCA) were selected for an international collaborative trial. Recovery of 15 pure strains was tested in the prestudy and recovery of one strain from foodstuffs was tested in the collaborative trial. Results from the prestudy did reveal statistical difference of the media but recoveries on all media were within the microbiological limits (+/-30%) of IS, which was set as a reference medium. Recoveries on the media tested in the collaborative trial were statistically different as well, but these differences were of no microbiological-analytical relevance. Food matrices did not affect the recovery of C. perfringens in general. DCA and SCA, in particular, are labor-intensive to prepare and DCA frequently failed to produce black colonies; gray colonies were quite common. Since IS medium is nonselective, it was concluded that TSC was the most favorable medium for the enumeration of C. perfringens from foods.

Animals↗

PubMed2003

Tolerance of Salmonella Enteritidis and Staphylococcus aureus to surface cleaning and household bleach.

Effective cleaning and sanitizing of food preparation sites is important because pathogens are readily spread to food contact surfaces after preparation of contaminated raw products. Tolerance of Salmonella Enteritidis and Staphylococcus aureus to surface cleaning by wiping with regular, microfiber, and antibacterial-treated cloths was investigated. Wiping with cleaning cloths resulted in a considerable reduction of microorganisms from surfaces, despite the greater difficulty in removing S. aureus than Salmonella Enteritidis. Depending on the cloth type, S. aureus were reduced on surfaces from initial numbers of approximately 10(5) CFU/100 cm2 to numbers from less than 4 CFU/100 cm2 (below the detection limit) to 100 CFU/100 cm2. Directly after the cloths were used to clean the contaminated surfaces, they contained high numbers of bacteria (10(4) to 10(5) CFU/100 cm2), except for the disposable antibacterial-treated cloths, in which no bacteria could be detected. The tolerance of these pathogens to sodium hypochlorite was studied in the suspension test and in cloths. S. aureus showed a better tolerance for sodium hypochlorite than Salmonella Enteritidis. Inactivation of microorganisms in cloths required a higher concentration of sodium hypochlorite than was needed in the suspension test. Repeated exposure to sodium hypochlorite, however, resulted in an increase in susceptibility to this compound. This study provides essential information about the transfer of bacteria when wiping surfaces and highlights the need for a hygiene procedure with cleaning cloths that sufficiently avoids cross-contamination in the household environment.

Bacterial Adhesion↗

PubMed2002

Effects of antibacterial dishwashing liquid on foodborne pathogens and competitive microorganisms in kitchen sponges.

In response to increasing concern about home hygiene, the use of antibacterial products to reduce microorganisms in kitchen sponges and cleaning cloths is strongly promoted by some producers of detergent for domestic use. The effects of an antibacterial dishwashing liquid on Escherichia coli, Salmonella Enteritidis, Staphylococcus aureus, and Bacillus cereus were investigated in a modified suspension test and in used sponges with and without food residues under laboratory conditions. A limited study was conducted in households to assess the efficacy of antibacterial dishwashing liquid as used by the consumer. In the suspension tests, S. aureus and B. cereus were shown to be susceptible to low concentrations of antibacterial dishwashing liquid (0.5%), whereas E. coli and Salmonella Enteritidis maintained their initial numbers for at least 24 h at 25 degrees C. At higher concentrations (2 to 4%), all test organisms decreased to below the detection limit after 24 h. Over a 24-h period, the antibacterial dishwashing liquid did not significantly reduce these organisms in used sponges in which food residues were present. The antibacterial product did not reduce the competitive microorganisms either. Similar results were found for sponges involved in daily household use. The results of this study demonstrate that the antibacterial dishwashing liquid was effective in reducing pathogens in the suspension test but not in the used sponges. This finding indicates that to determine the efficacy of antibacterial products, their use in a household setting must be considered.

Bacillus cereus↗

PubMed2002

Optimizing sporulation of Clostridium perfringens.

Many sporulation media have been developed for Clostridium perfringens, but none stimulates sporulation for all strains. The aim of our experiments was to develop a sporulation method using Duncan and Strong (DS) medium, which supports sporulation of a wide variety of strains. Different inoculation levels were tested, and the effects of sporulation-promoting substances and acid shock were evaluated. Furthermore, DS medium was compared with other sporulation media. Highest spore numbers in DS medium were obtained with a 10% 24-h fluid thioglycollate broth inoculum (5.0 x 10(5)/ml). Addition of theophylline and replacement of starch by raffinose increased spore yields for some strains, but most strains were not affected (average increases in log N/ml of 0.2 and 0.3, respectively). One strain was enhanced by the addition of bile, but other strains were strongly inhibited (average decrease in log N/ml of 2.5); agar did not influence sporulation. Neither short-time acid exposure nor addition of culture supernatant fluids of well-sporulating strains resulted in higher spore numbers in DS medium. None of the tested methods enhanced sporulation in general; only strain-dependent effects were obtained. Peptone bile theophylline medium was the most promising sporulation medium tested; peptone bile theophylline starch medium yielded highest spore numbers (2.5 x 10(5)/ml), but some strains failed to sporulate. In conclusion, adding theophylline to DS medium may optimize sporulation of C. perfringens, but peptone bile theophylline medium with or without starch is most suitable.

Clostridium perfringens↗

PubMed2000

Stepwise quantitative risk assessment as a tool for characterization of microbiological food safety.

This paper describes a system for the microbiological quantitative risk assessment for food products and their production processes. The system applies a stepwise risk assessment, allowing the main problems to be addressed before focusing on less important problems. First, risks are assessed broadly, using order of magnitude estimates. Characteristic numbers are used to quantitatively characterize microbial behaviour during the production process. These numbers help to highlight the major risk-determining phenomena, and to find negligible aspects. Second, the risk-determining phenomena are studied in more detail. Both general and/or specific models can be used for this and varying situations can be simulated to quantitatively describe the risk-determining phenomena. Third, even more detailed studies can be performed where necessary, for instance by using stochastic variables. The system for quantitative risk assessment has been implemented as a decision supporting expert system called SIEFE: Stepwise and Interactive Evaluation of Food safety by an Expert System. SIEFE performs bacterial risk assessments in a structured manner, using various information sources. Because all steps are transparent, every step can easily be scrutinized. In the current study the effectiveness of SIEFE is shown for a cheese spread. With this product, quantitative data concerning the major risk-determining factors were not completely available to carry out a full detailed assessment. However, this did not necessarily hamper adequate risk estimation. Using ranges of values instead helped identifying the quantitatively most important parameters and the magnitude of their impact. This example shows that SIEFE provides quantitative insights into production processes and their risk-determining factors to both risk assessors and decision makers, and highlights critical gaps in knowledge.

Cheese↗

PubMed1999

Methodology for detection and typing of foodborne microorganisms.

Over the past decade many improvements have been seen in both conventional and modern methods for the detection of pathogenic bacteria in foods. Modifications and automation of conventional methods in food microbiology include sample preparation, plating techniques, counting and identification test kits. ATP bioluminescence techniques are increasingly used for measuring the efficiency of cleaning surfaces and utensils. Cell counting methods, including flow cytometry and the direct epifluorescent filter technique are suitable techniques for rapid detection of microorganisms, especially in fluids. Automated systems based on impedimetry are able to screen high numbers of samples based on total bacterial counts within 1 day. Immunoassays in a wide range of formats make rapid detection of many pathogens possible. Recently, there have been important developments in the use of nucleic acid-based assays for the detection and subtyping of foodborne pathogens. The sensitivity of these methods has been significantly increased by the use of the polymerase chain reaction and other amplification techniques. Alternative and rapid methods must meet several requirements concerning accuracy, validation, speed, automation, sample matrix, etc. Both conventional and rapid methods are used within hazard analysis critical control point programs. Further improvements especially in immunoassays and genetic methods can be expected, including the use of biosensors and DNA chip technology.

Bacterial Typing Techniques↗

PubMed1999

Occurrence and survival of verocytotoxin-producing Escherichia coli O157 in meats obtained from retail outlets in The Netherlands.

In 1996 and 1997, 2,941 fresh and processed meat products obtained from supermarkets and butcher shops in The Netherlands were examined for the presence of verocytotoxin-producing Escherichia coli of serogroup O157 (O157 VTEC). Additionally, the fate of O157 VTEC in raw meat products stored at low temperatures and the effect of different additives were evaluated. O157 VTEC strains were isolated from 6 (1.1%) of 571 samples of raw minced beef, 2 (0.5%) of 402 samples of raw minced mixed beef and pork, 1 (1.3%) of 76 samples of raw minced pork, 1 (0.3%) of 393 samples of other raw pork products, and 1 (0.3%) of 328 samples of cooked or fermented ready-to-eat meats. Other raw beef products (n = 223) and meat samples originating from poultry (n = 819), sheep or lamb (n = 46), or wild animals (n = 83) were all found to be negative for O157 VTEC. For the survival experiments we used tartaar (minced beef with a fat content of less than 10%) and filet americain (tartaar mixed with a mayonnaise-based sauce [80 to 20%]). The O157 VTEC strain tested was able to survive in tartaar and filet americain stored at -20, 0, 5, or 7 degrees C for 3 days. At both 7 and at 15 degrees C, O157 VTEC counts in tartaar and filet americain remained virtually unchanged throughout a storage period of 5 days. Addition of acetic acid (to pH 4.0), sodium lactate (1 and 2% [wt/wt]), or components of the lactoperoxidase-thiocyanate-hydrogen peroxide system to filet americain did not result in a reduction of viable O157 VTEC cells during storage at 7 or 15 degrees C. It was concluded that raw meat contaminated with O157 VTEC will remain a hazard even if the meat is held at low or freezing temperatures.

Animals↗

PubMed1998

[Isolation, identification and characterization of Bacillus cereus in the dairy industry].

In order to determine the major contamination sources of milk with (psychrotrophic) Bacillus cereus, the incidence of vegetative cells and spores of B. cereus on dairy farms, at two dairy processing plants and in pasteurized milk in household refrigerators was investigated. On dairy farms the major contamination sources were soil and faeces. In winter, when the cows were housed, used bedding probably also participates in this contamination route. The udder will be contaminated, finally resulting in the presence of B. cereus in raw milk. The organism could be detected in 35% of the raw milk samples analyzed. During processing, an increase in the percentage of positive samples was observed. These results suggest that B. cereus can be introduced via sources other than raw milk; equipment may play an important role in this. Biochemical and molecular typing showed that selection of strains takes place in the milk production chain. It was demonstrated that some types were found in the raw milk, during processing and in the end products, indicating that raw milk is an important source of contamination. Other types could only be detected after the pasteurization step in the production process supporting the assumption that additional contamination occurs during processing. If stored under proper conditions, maximum storage temperature 7 degrees C, and consumed within the expiration date, the levels of B. cereus in pasteurized milk will, in general, not exceed 10(5) per ml and cause no problems for healthy adults.

Animals↗

PubMed1998

Occurrence and survival of verocytotoxin-producing Escherichia coli O157 in raw cow's milk in The Netherlands.

From May through November 1997, 1,011 samples of raw milk from bulk storage tanks were examined for the presence of verocytotoxin-producing Escherichia coli of serogroup O157 (O157 VTEC) by immunomagnetic separation following selective enrichment. The samples originated from 1,011 different dairy herds located throughout the Netherlands. O157 VTEC was not isolated from any of the milk samples examined. Additionally, survival of O157 VTEC in raw and UHT-sterilized cow's milk at 7 and 15 degrees C was studied, both in the absence and presence of an activated lactoperoxidase-thiocyanate-hydrogen peroxide system (LPS). Results indicated that the O157 VTEC strain tested was able to grow in raw milk at 7 degrees C as well as at 15 degrees C. Naturally occurring amounts of thiocyanate and hydrogen peroxide in the raw milk tested were not sufficient to activate the LPS. Although the LPS exhibited an antimicrobial activity against O157 VTEC in LPS-activated sterilized milk, O157 VTEC populations were not (or not as obviously) reduced in LPS-activated raw milk. Possibly background microflora were more sensitive to the LPS than the O157 VTEC test strain. It was concluded that raw milk contaminated with O157 VTEC will remain a hazard if kept at 7 or 15 degrees C. Effective pasteurization and avoiding postpasteurization contamination are necessary to ensure the safety of milk.

Animals↗

PubMed1997

Isolation and characterisation of Bacillus cereus from pasteurised milk in household refrigerators in The Netherlands.

The incidence and some characteristics (carbohydrate metabolism, growth profiles, haemolysin production and enterotoxin production) of Bacillus cereus, in pasteurised, low-fat (1.5%) milk, in household refrigerators in the Netherlands was investigated. In 247 (74%) of the 334 milk samples analyzed, the mesophilic aerobic counts were between 50 and 5000 per millilitre. B. cereus could be isolated from 133 (40%) of the samples. In general the B. cereus counts were low; numbers of less than five per millilitre were observed in 258 (77%) of the samples. As expected, both the mesophilic aerobic counts and levels of B. cereus increased with increasing storage temperatures in the refrigerator and prolonged storage times. In total, 143 presumptive B. cereus colonies were isolated. According to the ISO confirmation tests and the carbohydrate patterns (API 50 CHB) 134 (94%) of these isolates were confirmed to be B. cereus. Of these 134 isolates 20% fermented lactose and 53% of the 106 strains tested were able to grow at 7 degrees C. These percentages are much higher than expected for strains isolated from non-dairy products, suggesting that strains can adapt to environmental conditions in milk. All 106 strains tested, produced haemolysin, 27% showed the discontinuous haemolytic pattern characteristic for haemolysin BL, possibly a virulence factor. Of the 37 B. cereus isolates tested for enterotoxin production 27 (73%), 28 (76%) and 26 (70%) were found to be enterotoxigenic (as determined by the Western immunoblot technique, polymerase chain reaction (PCR) and Vero cell assays, respectively). Isolates unable to ferment lactose, produced less enterotoxin in comparison with those able to utilize lactose. Although only a few outbreaks of food poisoning caused by B. cereus in milk (products) have been reported, most strains isolated from these products are able to produce enterotoxins and may represent a health hazard.

Animals↗

PubMed1997

Discrimination between Bacillus cereus and Bacillus thuringiensis using specific DNA probes based on variable regions of 16S rRNA.

Identification of Bacillus cereus and differentiation between B. cereus and closely related species are currently based on biochemical tests. The main problem is to discriminate between B. cereus and B. thuringiensis. Sequencing part of the 16S rRNA showed that several B. cereus isolates present in food and involved in food poisoning, confirmed according to the classical biochemical methods, were in fact B. thuringiensis. As this organism is the most commonly used microbial insecticide worldwide, the results of this study emphasize the need for accurate identification methods and for careful screening of strains for use as insecticides. Therefore, specific DNA probes based on the variable region VI of 16S rRNA of B. cereus and B. thuringiensis were designed. The probes were used in hybridization experiments with the variable region amplified using the polymerase chain reaction. In this way, a rapid and sensitive method was developed to distinguish B. cereus and B. thuringiensis.

Bacillus cereus↗

PubMed1997

Optimization of haemolysis in enhanced haemolysis agar (EHA)--a selective medium for the isolation of Listeria monocytogenes.

The presence of Listeria monocytogenes in enrichment media can be masked by faster growth of other Listeria spp. Therefore, enhanced haemolysis agar (EHA) is a good alternative for another isolation media, because the presence of a few L. monocytogenes colonies can be detected in a majority of colonies of other listeriae on the basis of haemolysis. In this study the haemolysis reaction in EHA was optimized. In a collaborative study using reference samples, no significant differences in counts on EHA, Palcam and Oxford agar were shown.

Agar↗

PubMed1996

Listeria species in domestic environments.

Using a direct isolation method Listeria spp. were detected in 101 (47.4%) of 213 houses investigated. L. monocytogenes was present in 45 houses (21.1%). Listeria spp. occurred at all sampling sites. Dish-cloths (37%) and surface samples round the drain in the bathroom (27.2%) were most frequently contaminated. Highest numbers (c. 10(4) c.f.u./object) were found in dish-cloths and washing-up brushes. Lower levels (up to 10(3) c.f.u./object) were obtained from kitchen sinks, refrigerator vegetable compartment samples and tooth brushes. In total, 132 isolations of Listeria spp. were made from 871 samples. L. innocua (53%) and L. monocytogenes (41%) were the predominant species in the positive samples. Other Listeria spp. were found in only 6% of the positive samples.

Environmental Microbiology↗