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S Notermans

Publications and source records attributed to S Notermans.

At least 19 recordsLinked to original sources
PubMed2001

Quantitative microbiological risk assessment.

The production of safe food is being increasingly based on the use of risk analysis, and this process is now in use to establish national and international food safety objectives. It is also being used more frequently to guarantee that safety objectives are met and that such guarantees are achieved in a cost-effective manner. One part of the overall risk analysis procedure-risk assessment-is the scientific process in which the hazards and risk factors are identified, and the risk estimate or risk profile is determined. Risk assessment is an especially important tool for governments when food safety objectives have to be developed in the case of 'new' contaminants in known products or known contaminants causing trouble in 'new' products. Risk assessment is also an important approach for food companies (i) during product development, (ii) during (hygienic) process optimalization, and (iii) as an extension (validation) of the more qualitative HACCP-plan. This paper discusses these two different types of risk assessment, and uses probability distribution functions to assess the risks posed by Escherichia coli O157:H7 in each case. Such approaches are essential elements of risk management, as they draw on all available information to derive accurate and realistic estimations of the risk posed. The paper also discusses the potential of scenario-analysis in simulating the impact of different or modified risk factors during the consideration of new or improved control measures.

Animals↗
PubMed2000

Risk assessment of Listeria monocytogenes in fish products: some general principles, mechanism of infection and the use of performance standards to control human exposure.

Risk assessment is increasingly used as a scientific process to assess the potential for adverse health effects to occur and as a basis for management of unacceptable risks. For each risk assessment activity, the purpose of the assessment should be clearly stated. For Listeria monocytogenes, the purpose of risk assessment may be providing information on the relative contribution of listeriosis to infectious diseases. For control purposes, the emphasis may be put on factors contributing to the risk of occurrence in a food or to inform risk managers that they should be setting food safety objectives. For an adequate risk assessment of L. monocytogenes, sound scientific data are necessary. This especially applies both to exposure assessment and hazard characterisation. Surveillance data indicates that cold storage to prolongs product shelf-life has opened an ecological window for the growth of L. monocytogenes. Assessment of dose-response relationship is often regarded as a key element in risk characterisation. Due to the large variability of the current assessed dose-response data, their contribution to assessing risks is low. The use of epidemiological data on incidence rate, types of food involved in listeriosis, etc. may be good alternatives. The use of performance standards or criteria, such as inactivation by heat or by fermentation, combined with processes that prevent outgrowth of the organism should be reconsidered. Presently, performance standards can simply be assessed since mathematical tools for their calculations are becoming increasingly available.

Animals↗
PubMed2000

Effects of combined exposure of micrococcus luteus to nisin and pulsed electric fields.

Death and injury following exposure of Micrococcus luteus to nisin and pulsed electric field (PEF) treatment were investigated in phosphate buffer (pH 6.8, sigma = 4.8 ms/cm at 20 degrees C). Four types of experiment were carried out, a single treatment with nisin (100 IU/ml at 20 degrees C for 2 h), a single PEF treatment, a PEF treatment followed by incubation with nisin (as before) and addition of nisin to the bacterial suspension prior to the PEF treatment. The application of nisin clearly enhanced the lethal effect of PEF treatment. The bactericidal effect of nisin reduced viable counts by 1.4 log10 units. Treatment with PEF (50 pulses at 33 kV/cm) resulted in a reduction of 2.4 log10 units. PEF treatment followed by nisin caused a reduction of 5.2 log10 units in comparison with a 4.9 log10 units reduction obtained with nisin followed by PEF. Injury of surviving cells was investigated using media with different concentrations of salt. Sublethally damaged cells of M. luteus could not be detected by this means, following PEF treatment.

Anti-Bacterial Agents↗
PubMed2000

Pulsed electric fields inactivation of attached and free-living Escherichia coli and Listeria innocua under several conditions.

The use of pulsed electric fields (PEF) is considered as a mild process in the inactivation of microorganisms present in liquid food products. PEF treatments of Escherichia coli and Listeria innocua suspended in milk and phosphate buffer, with same pH and same conductivities, yielded to similar inactivation. Reduction rates obtained in distilled water indicated that conductivity of the food product is a main parameter in bacterial inactivation. Bacteria attached to polystyrene beads were inactivated by PEF at a greater (E. coli) or equal rate (L. innocua) than free-living bacteria. Base on the use of selective and non-selective enumeration media, no clear indications were obtained for sublethal damage of microorganisms surviving the PEF treatment. E. coli cells subjected to 60 pulses at 41 kV/cm were examined by transmission and scanning electron microscopy. Changes in the cytoplasm were observed and the cell surface appeared rough. The cells outer membranes were partially destroyed allowing leaking of cell cytoplasm.

Electricity↗
PubMed2000

Role of volatile fatty acids in development of the cecal microflora in broiler chickens during growth.

It is known that volatile fatty acids can inhibit growth of species of the family Enterobacteriaceae in vitro. However, whether these volatile fatty acids affect bacterial populations in the ceca of chickens is unknown. Therefore, a study was conducted to investigate if changes in volatile fatty acids in ceca of broiler chickens during growth affect bacterial populations. Results showed that members of the Enterobacteriaceae and enterococci are present in large numbers in 3-day-old broilers and start to decrease when broilers grow older. Lactobacilli are present in large numbers as well in 3-day-old broilers, but they remain stable during the growth of broilers. Acetate, butyrate, and propionate increase from undetectable levels in 1-day-old broilers to high concentrations in 15-day-old broilers, after which they stabilize. Significant negative correlations could be calculated between numbers of Enterobacteriaceae and concentrations of undissociated acetate, propionate, and butyrate. Furthermore, pure cultures of Enterobacteriaceae isolated from the ceca were grown in the presence of volatile fatty acids. Growth rates and maximal optical density decreased when these strains grew in the presence of increasing volatile fatty acid concentrations. It is concluded that volatile fatty acids are responsible for the reduction in numbers of Enterobacteriaceae in the ceca of broiler chickens during growth.

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↗
PubMed1997

An identification procedure for foodborne microbial hazards.

A stepwise and interactive identification procedure for foodborne microbial hazards has been developed in which use is made of several levels of detail ranging from rough hazard identification to comprehensive hazard identification. This approach allows one to tackle the most obvious hazards first, before focusing on less obvious hazards. The interactive character of the identification procedure is based on the use of several knowledge sources. Combination of knowledge sources, expressed in the use of knowledge rules, supports the user in systematically selecting hazards which may pose a real risk to the consumer. Due to the structured method and the clear definitions of the knowledge rules, the procedure is transparent and may be changed if necessary. The hazard identification procedure has been implemented as a computer program, resulting in a decision-supporting identification system. It provides a way to efficiently assess those hazards which may cause harm if not brought under control during processing. The procedure forms a basis for quantitative risk assessments.

Animals↗
PubMed1996

Quantitative risk analysis and the production of microbiologically safe food: an introduction.

There is increasing interest in the application of quantitative risk analysis (QRA) in the production of microbiologically safe food products. QRA can be defined as a stepwise analysis of health risks which may be associated with a particular type of food product, resulting in an estimation of the probability of occurrence of negative health effects following the consumption of that food and the nature of these risks. Starting with this definition, the following successive components can be recognised: (1) hazard identification, which is a qualitative indication of the potential microbial hazards that may be associated with the consumption of a particular food product; (2) exposure assessment, which is the quantitative estimation of the dose of potentially hazardous organisms to which the consumer is exposed at the time of consumption of the food; (3) dose response assessment, which is the process of obtaining quantitative information on the negative effects of different levels of exposure to potentially hazardous organisms on the health of the consumer; (4) risk characterization, which comprises the activities that are carried out to rank the disorders according to severity, perception, economic and social consequences etc., enabling a decision to be made about the acceptance of a particular risk; and (5) risk management, which is the complex of analyses and judgements to reduce the probability of occurrence of unacceptable risks.

Consumer Product Safety↗
PubMed1996

Application of predictive microbiology to estimate the number of Bacillus cereus in pasteurised milk at the point of consumption.

A procedure is presented to quantitatively estimate the growth of a particular organism in a food product during chilled storage using predictive microbiology. This results in a quantification of the contribution of every individual process step to the total number of organisms, which may be a useful tool to support decisions on existing process lines as well as in process and product design. It is demonstrated that predictive microbiology will only estimate to within orders of magnitude of bacterial growth. This helps to pinpoint the most important aspects of a line. The calculations can be helpful to set critical limits and to detect hazards by performing 'what if' analyses. The procedure is explained for the growth of Bacillus cereus in milk. It is indicated, that with the current information, the effect of time/temperature can be estimated. However, to make an accurate exposure analysis, more information will be needed.

Animals↗
PubMed1996

Incorporation of elements of quantitative risk analysis in the HACCP system.

Foodborne bacterial diseases cause considerable morbidity and mortality throughout the world. Preventive measures such as good manufacturing practices (GMP), supplemented by the hazard analysis critical control point (HACCP) system, have been introduced as a means of ensuring the production of safe food. However, their use does not necessarily provide quantitative information on the risks associated with the consumption of a particular food product. To obtain such information, elements of quantitative risk analysis (QRA) need to be used. QRA is defined as a stepwise analysis of the health risks associated with a specific type of food product, resulting in an estimation of the probability of occurrence of adverse effects on health following consumption of the food in question. It also includes an analysis of the nature of the risks. Taking this definition, five successive steps can be recognized: hazard identification, exposure assessment, dose response assessment, risk characterization and risk management. Food production is a dynamic activity, involving changes in, e.g. the composition and microbial quality of raw materials due to seasonal variation. Also, there may be continuing changes in processing conditions and in product composition due to consumer demands. Therefore, it will be desirable to incorporate QRA in existing safety assurance systems, such as HACCP, when sufficient information is available to permit this approach.

Bacterial Infections↗
PubMed1996

Food products and consumer protection: a conceptual approach and a glossary of terms.

There is greatly increased activity in measures being taken to ensure the production of safe food. Several concepts, increasingly based on quantitative risk analysis, are being introduced and new terminology and definitions are being proposed. This article presents a general approach to the production of microbiologically safe food and a glossary of appropriate terms. Where possible, an attempt is made to provide a more adequate terminology, based on that used in risk analysis; background information is also presented.

Consumer Product Safety↗
PubMed1995

Probes and polymerase chain reaction for detection of food-borne bacterial pathogens.

DNA-hybridization and the polymerase chain reaction (PCR) are techniques commonly used to detect pathogenic bacteria. In this paper, the use of these techniques for detection of Salmonella, E. coli, V. cholerae, non-O1 Vibrio, Yersinia enterocolitica, Campylobacter, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, and C. botulinum is reviewed with emphasis on application in food microbiology. In food control, DNA-techniques have most often been used in a 'culture confirmation' fashion, i.e. bacteria are enriched and sometimes even purified by traditional culture procedures and thereafter identified by the use of DNA-based methods. The most desirable approach is, however, to detect organisms directly in the food, but major problems remain to be solved before this can be routinely performed.

Bacteria↗
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

Microbiological challenge testing for ensuring safety of food products.

Microbiological challenge testing (MCT), storage testing, and predictive modelling are tools to simulate or to test what can happen to a food product during processing, distribution and subsequent handling. MCT is carried out if the microorganism of interest is suspected to be present in low numbers or only incidentally, and should be applied if full knowledge about the characteristics of a potential hazardous microorganism does not exist. MCT involves: (a) an appropriate experimental design; (b) an inoculation procedure; (c) a test procedure; and (d) interpretation of results. If MCT is carried out properly, information is obtained on the types of microorganisms capable of growth in the product, so that risks of food poisoning can be assessed. Therefore, the information obtained can be the basis for setting safety criteria at the critical control points in a food processing operation. However, it remains necessary to verify the test results under field conditions.

Food Handling↗
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↗