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.

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.

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.

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.

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.

EEG findings in patients with vascular parkinsonism.

OBJECTIVES: To investigate whether the conventional and quantitative EEGs of patients with vascular parkinsonism (VP) differ from those of idiopathic Parkinson's disease (PD) patients. MATERIAL AND METHODS: The EEGs of 13 patients with vascular parkinsonism and 14 patients with idiopathic Parkinson's disease were scored on a simple scale regarding aspects of conventional EEG variables. Alpha band power asymmetry and EEG slowing (increased delta and theta power) were calculated by the neurometrics method of quantitative EEG data evaluation. RESULTS: Analysis of both conventional and quantitative EEG data shows that VP patients had significantly less EEG slowing than PD patients. CONCLUSION: This study shows that the EEG in a group of patients with vascular parkinsonism differ from a patient group with idiopathic Parkinson's disease. Our results indicate that VP patients are not PD patients with subcortical vascular lesions, because then they would have had at least as much EEG slowing as PD patients.

The occurrence of fumonisin B1 in maize-containing foods in The Netherlands.

Seventy-eight maize-containing foods obtained from retail stores in The Netherlands were analysed for fumonisin B1 contamination. Thirty-six per cent of the samples were contaminated with fumonisin B1 in the range of 8 micrograms kg-1 (limit of detection) to 1430 micrograms/kg-1. Forty-six per cent of the minimally treated maize samples (n = 39; maize for bread production, maize for popcorn, maize flour and polenta) were contaminated with fumonisin B1 in the range of 8-380 micrograms kg-1. Twenty-six per cent of the maize-containing processed foods (n = 39; tostada, canned maize, maize starch, maize bread, popped maize, flour mixes, maize chips and cornflakes) were contaminated with fumonisin B1 in the range of 8-1430 micrograms/kg-1. This survey shows that maize-containing foods in The Netherlands frequently can be contaminated with fumonisin B1.

Fumonisin B1 in maize for food production imported in The Netherlands.

Sixty-two samples of maize imported in The Netherlands and intended for human consumption were screened for the presence and concentration of fumonisin B1. Sixty-one of those samples contained fumonisin B1 with concentrations ranging from 30 to 3350 micrograms kg-1, 11 maize samples contained > 1000 micrograms kg-1. The average fumonisin B1 concentration was 640 micrograms kg-1 for the positive samples and 620 micrograms kg-1 for all samples. Medians were 600 micrograms kg-1 and 550 micrograms kg-1 for positive and all samples, respectively. The results obtained were comparable to results from other studies in maize from various countries.

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.

Assessment of human exposure to fumonisin B1.

Fumonisin B1 is currently regarded as the most significant mycotoxin produced by Fusarium spp. It has carcinogenic properties and may play a role in the etiology of human esophageal cancer. The human population is exposed to fumonisin B1 primarily by intake of fumonisin B1-contaminated maize. Maize consumed in the Netherlands is imported from all parts of the world. Since processing will not affect the overall toxic effect, the fumonisin B1 intake is directly related to the quantity of maize consumed. Literature results concerning the occurrence of fumonisin B1 in a total of 349 samples of maize from 18 countries worldwide demonstrated the presence of this mycotoxin in 93% of the samples. The median fumonisin B1 contamination of all samples was 420 ng of fumonisin B1 per g of maize, and the average contamination level was 1,359 ng of fumonisin B1 per g of maize. Human intake of fumonisin B1 was estimated based on the maize consumption of all people in the Netherlands in 1992. A probability distribution was derived to allow estimation of the exposure of the population to fumonisin B1 intake in relation to maize intake. It showed that among those in the group considered to be at risk, people with gluten intolerance such as people with celiac or Dühring's disease, 37% are estimated to be exposed to an intake of at least 10(5) ng and 97% to an intake of at least 10(3) ng of fumonisin B1 per person per day. For all people in the Netherlands these percentages would be 1% and 49%, respectively.

Towards internationally acceptable standards for food additives and contaminants based on the use of risk analysis.

Internationally acceptable norms need to incorporate sound science and consistent risk management principles in an open and transparent manner, as set out in the Agreement on the Application of Sanitary and Phytosanitary Measures (the SPS Agreement). The process of risk analysis provides a procedure to reach these goals. The interaction between risk assessors and risk managers is considered vital to this procedure. This paper reports the outcome of a meeting of risk assessors and risk managers on specific aspects of risk analysis and its application to international standard setting for food additives and contaminants. Case studies on aflatoxins and aspartame were used to identify the key steps of the interaction process which ensure scientific justification for risk management decisions. A series of recommendations were proposed in order to enhance the scientific transparency in these critical phases of the standard setting procedure.

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.

The effect of previous growth conditions on the lag phase time of some foodborne pathogenic micro-organisms.

In current models for predicting microbial growth, the lag phase duration is expressed as a function of the growth rate of the micro-organism. We observed that in addition to the growth rate (as influenced by incubation temperature and NaCl contents), the pre-incubation temperature influences the lag phase duration of foodborne pathogenic micro-organisms.

Subclinical beriberi polyneuropathy in the low income group: an investigation with special tools on possible patients with suspected complaints.

OBJECTIVE: To determine the prevalence rate of subclinical beriberi polyneuropathy (PNP) in the low income group and to present new methods for early detection. DESIGN: We conducted a prospective, randomized observational study on all patients from family members of non-PNP patients presenting to the outpatient neurologic clinic of the Dr Soetomo Hospital in 1989 in Surabaya, Indonesia. MATERIAL AND METHODS: The 53 group I patients belonged to the low income series, whereas the 56 group II patients were from the mid- and high-income groups. We analyzed their diets and determined their blood thiamine levels. Neurologic, internal, psychiatric as well as neurophysiologic examinations were performed on all patients. RESULTS: The prevalence rate of subclinical beriberi PNP of the apparently healthy subjects of the low income group was 66% compared with 12.5% among the mid and high income groups. The exposure odds ratio was 13.6 (95% Cl, 2.78 to 8.04) indicating that the low income group ran a greater risk of developing beriberi PNP than the mid and high income groups. CONCLUSION: Most of our low income group patients had an inadequate diet, especially concerning deficient thiamine intake. Analysis of the diets revealed, that they were usually rich in carbohydrate especially steamed milled rice, whereas intake of fat and thiamine was low, protein was just sufficient. The calorie intake was marginal. Carbohydrate rich and non fat calories in the diet with low thiamine intake may provoke beriberi.

Akinetic mutism with bithalamic infarction. Neurophysiological correlates.

A 42-year-old man presented with akinetic mutism, caused by bilateral thalamic infarction, resulting in a temporary amnesic syndrome and, finally, selective downgaze palsy. Electroencephalographic recording in the initial phase showed generalized spike- and-wave discharges, similar to those found in animal studies after lesion or stimulation of specific thalamic nuclei. Analysis of magnetic resonance images (MRI) of the head showed that the centre of ischemic necrosis particularly involved the intralaminar thalamic nuclei and a small part of the rostral mesencephalon. The findings support the previously suggested involvement of cortico-thalamo-mesencephalic circuitry in the initiation of motor responses, and the association of the non-specific thalamic nuclei with the appearance of generalized epileptiform phenomena in cases of reduced vigilance.

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.

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.