Home style frying of steak and meat products: Survival of Escherichia coli related to dynamic temperature profiles.

Microbial survival of heating and cross-contamination are the two transmission routes during food preparation in the consumers' kitchen that are relevant for QMRA (Quantitative Microbial Risk Assessment). The aim of the present study was to extend the limited amount of data on microbial survival during real-life preparation of meat and meat products and to obtain accessory temperature data that allow for a more general (product unspecific) approach. Therefore survival data were combined with extensive measurements of time- and location dependent temperature using an infrared camera for the surface and buttons for the inside of the product, supplemented with interpolation modelling. We investigated the survival of heating of Escherichia coli O111:H2 in beefsteak, hamburgers (beef and 50% beef 50% pork (HH)), meatballs (beef and HH) and crumbs (HH). For beefsteak, survival as a whole is dominated by the sides, giving a log reduction of 1-2 (rare), 3-4 (medium) and 6-7 (done). Limited measurements indicated that done preparation gave 5-6 log reduction for crumbs and at least 8-9 log for the other products. Medium preparation gave a higher reduction in hamburgers (2-4 log) than in meatballs (1-2 log) and in beef (3-4) than in HH (2-3) hamburgers. In general, our 'done' results give larger inactivation than found in literature, whereas 'rare' and 'medium' results are similar. The experiments resulted in two types of curves of D70/z-values, dependent on product, doneness and for beefsteaks sides vs. top/bottom. One type of curve agrees reasonably with literature D70/z estimates from isothermal temperature experiments, which supports using these estimates for home style cooking QMRA calculations. In case of the other type of curve, which is mainly found for (near) surface contamination in close contact with the pan, these literature estimates cannot be applied. We also applied a simplified approach, assuming thermal inactivation is dominated by the highest temperatures reached. The time duration of this highest temperature gives accessory D-values which prove to fit with isothermal temperature literature data, thus suggesting application of such data for QMRA is possible by this approach also, which is less labor intensive both in terms of measurements and modelling. In real life, variability in product properties and preparation styles is large. Further studies are needed to analyze the effect on survival, preferably focusing on determining the essential variables. More variation in heating time will allow for estimating D70/z point estimates rather than curves representing possible sets of D70/z-values.

Modelling of inactivation through heating for quantitative microbiological risk assessment (QMRA).

EFSA regards the household as a stage in the food chain that is important for the final number of food-borne infections. The fate of a pathogen in the private kitchen largely depends on consumer hygiene during preparation of food and on its proper cooking, especially in the case of meat. Unfortunately, detailed information on the microbiological survival in meat products after heating in the consumer kitchen is lacking. The aim of the study was to improve the estimation of the inactivating effect on pathogens by heating meat or a meat product by the consumer in the kitchen. On that account, artificially contaminated meat and meat products were cooked according to several degrees of doneness and simulating real world conditions, and bacterial survival was measured. Heat camera pictures and button temperature loggers inserted into the food matrix served to record time and the temperature of heating. Temperature, time and the microbial survival ratio observed served to inform a mathematical model able to explain the thermal inactivation of meat or a meat product in home settings. The results of the study would help to improve microbiological comparative exposure assessments of pathogens in food, as an attribution tool and as a supportive tool for risk-based sampling in monitoring and surveillance.

High reward expectancy during methylphenidate depresses the dopaminergic response to gain and loss.

Dopamine plays an important role in goal-directed behavior, through its modulatory influence on striatal neurons. It is unclear whether tonic dopamine levels, which regulate the vigor of acting, interact with the phasic dopamine response to reward that drives instrumental behavior. In a randomized placebo-controlled study in healthy volunteers, we show that methylphenidate, a drug that increases tonic dopamine levels, systematically reduced striatal phasic BOLD responses to gain and loss in a gambling task as measured with fMRI. It also increased response vigor and reward expectancy-related BOLD signals in the ventral striatum. These findings suggest that striatal tonic dopamine levels constitute an average reward expectation signal that modulates the phasic dopaminergic response to reward. This offers opportunities for treatment of behavioral disorders associated with abnormal reward sensitivity.

Modeling of Salmonella Contamination in the Pig Slaughterhouse.

In this article we present a model for Salmonella contamination of pig carcasses in the slaughterhouse. This model forms part of a larger QMRA (quantitative microbial risk assessment) on Salmonella in slaughter and breeder pigs, which uses a generic model framework that can be parameterized for European member states, to describe the entire chain from farm-to-consumption and the resultant human illness. We focus on model construction, giving mathematical formulae to describe Salmonella concentrations on individual pigs and slaughter equipment at different stages of the slaughter process. Variability among individual pigs and over slaughterhouses is incorporated using statistical distributions, and simulated by Monte Carlo iteration. We present the results over the various slaughter stages and show that such a framework is especially suitable to investigate the effect of various interventions. In this article we present the results of the slaughterhouse module for two case study member states. The model outcome represents an increase in average prevalence of Salmonella contamination and Salmonella numbers at dehairing and a decrease of Salmonella numbers at scalding. These results show good agreement when compared to several other QMRAs and microbiological studies.

Mode of delivery and subsequent fertility.

STUDY QUESTION: When compared with vaginal delivery, is Cesarean delivery associated with reduced childbearing, a prolonged inter-birth interval or infertility? SUMMARY ANSWER: Women whose first delivery was by Cesarean section were not significantly different from those who delivered vaginally with respect to subsequent deliveries, inter-birth interval or infertility after delivery. WHAT IS ALREADY KNOWN: Some studies have suggested that delivery by Cesarean section reduces subsequent fertility, while others have reported no association. STUDY DESIGN, SIZE, DURATION: This was a planned secondary analysis of the Mothers' Outcomes After Delivery study, a longitudinal cohort study. This analysis included 956 women with 1835 deliveries, who completed a study questionnaire at 6-11 years (median [interquartile range]: 8.1 [7.1, 9.8]) after their first delivery. PARTICIPANTS/MATERIALS, SETTING, METHODS: Exclusion criteria regarding the first birth were: maternal age <15 or >50 years, delivery at <37 weeks gestation, placenta previa, multiple gestation, known fetal congenital abnormality, stillbirth, prior myomectomy and abruption. Of the 956 women included, the first delivery was by Cesarean section for 534 women and by vaginal birth for 422 women. Infertility was self-reported. To compare maternal characteristics by mode of first delivery, P-values were calculated using Fisher's exact test or Pearson's χ(2) test for categorical variables and a Kruskall-Wallis test for continuous variables. We also considered whether, across all deliveries to date, a prior Cesarean is associated with decreased fertility. In this analysis, self-reported infertility after each delivery (across all participants) was considered as a function of one or more prior Cesarean births, using generalized estimating equations to control for within-woman correlation. MAIN RESULTS AND THE ROLE OF CHANCE: No differences were observed between the Cesarean and vaginal groups (for first delivery) with respect to infertility after their most recent delivery (7 versus 6%, P = 0.597), the interval between their first and second births (30.8 versus 30.6 months, P = 0.872), or multiparity (75 versus 76%, P = 0.650). Across all births, a history of Cesarean delivery was not significantly associated with infertility (odds ratio [OR], 0.90; 95% confidence interval [CI], 0.64-1.26). Women who reported infertility prior to their first delivery were significantly more likely to report infertility after each subsequent delivery (OR, 5.16; 95% CI, 3.60-7.39). LIMITATIONS, REASONS FOR CAUTION: Due to the use of self-reported infertility, the fertility status of some participants may be misclassified. Also, the small sample size may result in insufficient power to detect small differences between groups. Finally, a relatively high proportion of our participants were over age 35 at the time of first delivery (26%) and highly educated (37% with graduate degrees), which may indicate that our population may not be generalizable. WIDER IMPLICATIONS OF THE FINDINGS: While some prior studies have shown decreased family size among women who deliver by Cesarean, our results suggest that the rate of infertility is not different after Cesarean compared with vaginal birth. Our findings should be reassuring to women who deliver by Cesarean section. STUDY FUNDING/COMPETING INTERESTS: This study was funded by the US National Institutes of Health (NIH, R01-HD056275). No competing interests are declared. TRIAL REGISTRATION NUMBER: N/A.

Methylphenidate reduces functional connectivity of nucleus accumbens in brain reward circuit.

Release of dopamine in the nucleus accumbens (NAcc) is essential for acute drug reward. The present study was designed to trace the reinforcing effect of dopamine release by measuring the functional connectivity (FC) between the NAcc and brain regions involved in a limbic cortical-subcortical circuit during a dopaminergic challenge. Twenty healthy volunteers received single doses of methylphenidate (40 mg) and placebo on separate test days according to a double-blind, cross-over study design. Resting state functional magnetic resonance imaging (fMRI) was measured between 1.5 and 2 h postdosing. FC between regions of interest (ROI) in the NAcc, the medial dorsal nucleus (MDN) of the thalamus and remote areas within the limbic circuit was explored. Methylphenidate significantly reduced FC between the NAcc and the basal ganglia (i.e., subthalamic nucleus and ventral pallidum (VP)), relative to placebo. Methylphenidate also decreased FC between the NAcc and the medial prefrontal cortex (mPFC) as well as the temporal cortex. Methylphenidate did not affect FC between MDN and the limbic circuit. It is concluded that methylphenidate directly affects the limbic reward circuit. Drug-induced changes in FC of the NAcc may serve as a useful marker of drug activity in in the brain reward circuit.

Acute tryptophan depletion alters the effective connectivity of emotional arousal circuitry during visceral stimuli in healthy women.

OBJECTIVE: Alterations in serotonin signalling within the brain-gut axis have been implicated in the pathophysiology of irritable bowel syndrome (IBS) and is a treatment target. Acute tryptophan depletion (ATD) decreases brain serotonin (5-hydroxytryptamine; 5-HT) levels, and increases visceral perception and negative emotional bias in patients with IBS. The aim of the present study was to determine the effect of ATD on brain activity and connectivity during visceral stimuli in healthy women, and to compare the ATD-induced brain connectivity of an arousal circuit in female patients with IBS without ATD. METHODS: 12 healthy females (19-25 years) were studied under placebo (PLA) conditions and ATD. Functional MRI measurements were performed during a rectal barostat protocol, consisting of random non-painful and maximal tolerable distensions. Partial least squares analyses and structural equation modelling were used to evaluate the effect of ATD on functional and effective brain connectivity during distension. Results in healthy controls under ATD were compared with the effective connectivity of brain responses to 45 mm Hg rectal distension in 14 female patients with constipation-predominant IBS (IBS-C) (24-50 years). RESULTS: In healthy controls, ATD resulted in increased response of an extensive brain network to balloon distension, including the amygdala and nodes of emotional arousal and homeostatic afferent networks. The effect was greater during high inflation, suggesting greater engagement of the central serotonion system with more aversive visceral stimuli. Effective connectivity analysis revealed a profound effect of ATD on coupling between emotional arousal network nodes, resulting in loss of negative feedback inhibition of the amygdala. A near-identical pattern was identified in the patients with IBS-C. CONCLUSIONS: The findings are consistent with an ATD-induced disinhibition of and increased connectivity within an emotional arousal network during aversive stimulation. Together with the previous demonstration of ATD-induced visceral hyperalgesia in healthy controls, and the near-identical effective connectivity pattern observed in patients with IBS-C, these findings suggest that dysregulation of this brain network may play a role in central pain amplification and IBS pathophysiology.

Increased neural activation during picture encoding and retrieval in 60-year-olds compared to 20-year-olds.

Brain aging has been associated with both reduced and increased neural activity during task execution. The purpose of the present study was to investigate whether increased neural activation during memory encoding and retrieval is already present at the age of 60 as well as to obtain more insight into the mechanism behind increased activity. Eighteen young (mean age 21.3) and 18 older (mean age 59.9) right-handed male participants were administered two picture memory tasks in an fMRI environment. Neural activation was measured during encoding and retrieval of pictures of natural scenes (landscapes) and physical objects. Results indicated reduced medial temporal activity during encoding in older participants and increased activity during both encoding and retrieval in several other areas in the brain, including the inferior and dorsolateral prefrontal cortices. This increased activation was not related to better memory performance. The present findings indicate that increased neural activation during memory tasks is present in individuals near the age of 60 compared to individuals near the age of 20, which extends findings from studies of more-advanced age groups. Also, increased activation was present even though cognitive performance at 60 was not as impaired as is generally found in more-advanced age groups. Although compensation is a plausible explanation of the increased activation at this age, we suggest that other mechanisms like disinhibition, dedifferentiation, or the recruitment of less-efficient cognitive strategies may be more likely.

The effects of acute tryptophan depletion on brain activation during cognition and emotional processing in healthy volunteers.

Acute tryptophan depletion (ATD), a method to temporarily lower central serotonin levels, has been used to study the functioning of the serotonergic system. Relatively recent studies that examined the effects of ATD on brain activation associated with cognitive and emotional processing in healthy volunteers are reviewed. An overview of the findings in healthy volunteers is important for the interpretation of the effect of ATD on brain activation in patients with an affective disorder, such as major depression. These studies show that during response control and negative feedback processing ATD modulates the BOLD response in the inferior/orbitofrontal cortex, the anterior cingulate cortex and the dorsomedial prefrontal cortex. During emotional processing, it is consistently found that ATD modulates the BOLD response in the amygdala. These brain regions also show abnormal activation in depressed patients. However, at the moment it remains unclear if the changes induced by ATD are related to decreased basal serotonin (5-HT) release or the result of other biochemical changes that are mediated by ATD. Future studies should implement methodological improvements, explore the possibilities of new promising imaging techniques and expand investigations into the effects of ATD on basal 5-HT release and other biochemical mechanisms that might be modulated by ATD.

Acute tryptophan depletion selectively attenuates cardiac slowing in an Eriksen flanker task.

In the present study, the effects of transiently lowering central serotonin levels by means of acute tryptophan depletion on measures of cognitive flexibility were examined. Flexible behaviour was measured in an Eriksen flanker task, and cardiac and electro-cortical responses to errors and congruent and incongruent stimuli were measured. The depletion was successful in lowering tryptophan levels and, as expected, it did not affect subjective mood. Depletion did not affect performance and electro-cortical measures and selectively affected cardiac measures. Depletion attenuated cardiac slowing to incongruent flanker stimuli but did not affect cardiac responses to congruent stimuli and errors. The selective effect on cardiac responses as compared to performance and electro-cortical measures was in accordance with earlier findings, as well as the attenuation of cardiac slowing. The selective effect on the cardiac response to incongruent stimuli was unexpected. Detailed analyses showed a close connection to the earlier reported attenuation of the cardiac response to negative feedback, and the effect is explained in terms of reduced anticipation of the feedback stimulus due to enhanced punishment prediction.

Serotonin and cognitive flexibility: neuroimaging studies into the effect of acute tryptophan depletion in healthy volunteers.

Cognitive flexibility is the ability to adjust behavior to changes in the environment or task conditions. Previous research suggested that serotonin (5-HT) is involved in cognitive flexibility. Disturbed 5-HT functioning in animals, psychiatric patients and healthy volunteers leads to more rigid behavior. A well recognized method to manipulate levels of brain 5-HT is acute tryptophan depletion (ATD). This method induces a transient and reversible lowering of plasma tryptophan that has been shown to result in decreased brain 5-HT. Only recently has ATD research been combined with functional Magnetic Resonance Imaging (fMRI). In this review, we discuss recent investigations into the effect of ATD on the Blood Oxygen Level Dependent (BOLD) response during tasks that require cognitive flexibility, in healthy volunteers. Functional MRI studies have shown that ATD changes brain activation during tasks that require cognitive flexibility. It is hypothesized that ATD changes the processing of negative feedback, rather than impairing response inhibition, impairing the response to an error or the loss of cognitive control during response interference. Although the results of these studies are intriguing, they are sometimes contradictory. This could be the result of the different paradigms that have been used. Importantly, these studies strongly suggest that future multidisciplinary research should evaluate the mechanisms underlying individual differences and control for variables that have been shown to interact with the effect of ATD on cognitive flexibility and the related brain activation.

European Federation of Neurological Societies/Peripheral Nerve Society guideline on management of multifocal motor neuropathy.

Several diagnostic criteria for multifocal motor neuropathy have been proposed in recent years and a beneficial effect of intravenous immunoglobulin (IVIg) and various other immunomodulatory drugs has been suggested in several trials and uncontrolled studies. The objectives were to prepare consensus guidelines on the definition, investigation and treatment of multifocal motor neuropathy. Disease experts and a patient representative considered references retrieved from MEDLINE and the Cochrane Library in July 2004 and prepared statements which were agreed in an iterative fashion. The Task Force agreed good practice points to define clinical and electrophysiological diagnostic criteria for multifocal motor neuropathy and investigations to be considered. The principal recommendations and good practice points were: (i) IVIg (2 g/kg given over 2-5 days) should be considered as the first line treatment (level A recommendation) when disability is sufficiently severe to warrant treatment. (ii) Corticosteroids are not recommended (good practice point). (iii) If initial treatment with IVIg is effective, repeated IVIg treatment should be considered (level C recommendation). The frequency of IVIg maintenance therapy should be guided by the individual response (good practice point). Typical treatment regimens are 1 g/kg every 2-4 weeks or 2 g/kg every 4-8 weeks (good practice point). (iv) If IVIg is not or not sufficiently effective then immunosuppressive treatment may be considered. Cyclophosphamide, ciclosporin, azathioprine, interferon beta1a, or rituximab are possible agents (good practice point). (v) Toxicity makes cyclophosphamide a less desirable option (good practice point).

European Federation of Neurological Societies/Peripheral Nerve Society guideline on management of paraproteinaemic demyelinating neuropathies: report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society.

BACKGROUND: Paraprotein-associated neuropathies have heterogeneous clinical, neurophysiological, neuropathological and haematological features. Objectives. To prepare evidence-based and consensus guidelines on the clinical management of patients with both a demyelinating neuropathy and a paraprotein (paraproteinaemic demyelinating neuropathy, PDN). METHODS: Search of MEDLINE and the Cochrane library, review of evidence and consensus agreement of an expert panel. RECOMMENDATIONS: In the absence of adequate data, evidence based recommendations were not possible but the panel agreed the following good practice points: (1) Patients with PDN should be investigated for a malignant plasma cell dyscrasia. (2) The paraprotein is more likely to be causing the neuropathy if the paraprotein is immunoglobulin (Ig)M, antibodies are present in serum or on biopsy, or the clinical phenotype is chronic distal sensory neuropathy. (3) Patients with IgM PDN usually have predominantly distal and sensory impairment, with prolonged distal motor latencies, and often anti-myelin associated glycoprotein antibodies. (4) IgM PDN sometimes responds to immune therapies. Their potential benefit should be balanced against their possible side-effects and the usually slow disease progression. (5) IgG and IgA PDN may be indistinguishable from chronic inflammatory demyelinating polyradiculoneuropathy, clinically, electrophysiologically, and in response to treatment. (6) For POEMS syndrome, local irradiation or resection of an isolated plasmacytoma, or melphalan with or without corticosteroids, should be considered, with haemato-oncology advice.

Serotonin and human cognitive performance.

In the past decade, experimental studies involving healthy human volunteers have revealed that manipulations of the central serotonin (5-HT) system can produce quite specific changes in cognitive functioning, independent of overt mood changes. Reduced 5-HT turnover is consistently associated with impaired long-term memory functioning. Low 5-HT function may also impair cognitive flexibility and improve focused attention. On the other hand, stimulation of central 5-HT has repeatedly been found to impair performance in a true vigilance task. Currently, there is little evidence for mirrored cognitive changes due to opposite 5-HT manipulations in healthy volunteers. Given the mounting evidence for a role of 5-HT in human cognition, reduced 5-HT function could be directly linked to cognitive disturbances in certain conditions, such as in depression and Alzheimer's Disease (AD). There is evidence that stimulating (i.e. normalizing) 5-HT activity in depression may have specific beneficial effects on cognition, independent of a general relief of depressive symptoms, but this premise needs to be confirmed by larger-scale clinical studies. Recently, a potential role of 5-HT in the cognitive symptoms in AD has been identified, but there is insufficient data to evaluate the effects of 5-HT stimulation on cognitive symptoms in AD. It is concluded that serotonin is a potential target for pharmacological cognition enhancement, particularly for restoration of impaired cognitive performance due to 5-HT dysfunction. Further differentiation of the role of 5-HT in normal and disturbed cognition and evaluation of the effects of 5-HT manipulations in various populations is required to establish the full potential of 5-HT drugs as cognition enhancers.

Acute tryptophan depletion improves performance and modulates the BOLD response during a Stroop task in healthy females.

To gain more insight into the effect of low brain serotonin (5-HT) on brain activation related to conflict, the present study examined the effect of acute tryptophan depletion (ATD) on performance and the blood oxygen level dependent (BOLD) response during a combined cognitive and emotional Stroop task. Fifteen healthy female volunteers were tested during a placebo and tryptophan depletion session in an event-related fMRI design. ATD improved performance during Stroop interference. Two effects of ATD on the BOLD response were found. Firstly, ATD increased the BOLD response in the anterior cingulate cortex (ACC) (BA 32) when incongruent color words were compared with congruent color words in the first Stroop block the participants performed. Secondly, ATD increased the BOLD response in the left precuneus (BA 31) and cuneus (BA 18) during congruent color words. ATD did not affect the BOLD response accompanying emotional stimuli. However, we showed that ATD increased the interference of negative words on color naming. This finding was explained in terms of an emotional processing bias in favor of negative words, which leads to stronger interference of these words. In line with previous studies, the present study showed that a temporary reduction of 5-HT improved Stroop performance and changed the underlying brain activation pattern in healthy female participants. Moreover, we replicated our previous finding that ATD modulated the BOLD response in the dorsomedial prefrontal cortex during tasks that require cognitive control.

European Federation of Neurological Societies/Peripheral Nerve Society guideline on management of chronic inflammatory demyelinating polyradiculoneuropathy: report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society.

Numerous sets of diagnostic criteria have sought to define chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and randomized trials and systematic reviews of treatment have been published. The objective is to prepare consensus guidelines on the definition, investigation and treatment of CIDP. Disease experts and a patient representative considered references retrieved from MEDLINE and Cochrane Systematic Reviews in May 2004 and prepared statements which were agreed in an iterative fashion. The Task Force agreed on good practice points to define clinical and electrophysiological diagnostic criteria for CIDP with or without concomitant diseases and investigations to be considered. The principal treatment recommendations were: (1) intravenous immunoglobulin (IVIg) or corticosteroids should be considered in sensory and motor CIDP (level B recommendation); (2) IVIg should be considered as the initial treatment in pure motor CIDP (Good Practice Point); (3) if IVIg and corticosteroids are ineffective plasma exchange (PE) should be considered (level A recommendation); (4) If the response is inadequate or the maintenance doses of the initial treatment are high, combination treatments or adding an immunosuppressant or immunomodulatory drug should be considered (Good Practice Point); (5) Symptomatic treatment and multidisciplinary management should be considered (Good Practice Point).

Effects of a novel method of acute tryptophan depletion on plasma tryptophan and cognitive performance in healthy volunteers.

RATIONALE: Disorders associated with low levels of serotonin (5-HT) are characterized by mood and cognitive disturbances. Acute tryptophan depletion (ATD) is an established method for lowering 5-HT levels and an important tool to study the effects of reduced 5-HT on mood and cognition in human subjects. The traditional ATD method, i.e., administration of separate amino acids (AAs), has several disadvantages. The AA mixture is costly, unpalatable and associated with gastrointestinal discomfort. OBJECTIVES: The University of Maastricht developed a new and inexpensive method for ATD: a natural collagen protein (CP) mixture with low tryptophan (TRP) content. The reductions in plasma TRP after taking this CP mixture were compared with the reductions achieved taking the traditional AA mixture, and effects on memory and reversal learning were studied. METHODS: Fifteen healthy young volunteers participated in a double-blind, counterbalanced within-subject study. Reversal learning, verbal memory and pattern recognition were assessed at baseline and 3-4 h after taking the CP mixture. RESULTS: The new ATD method significantly reduced plasma TRP by 74% and the ratio between TRP and the other large AAs (TRP/LNAA) by 82%. The placebo mixture did not change these measures. Delayed recognition reaction time on the verbal learning task was increased following ATD. No other cognitive effects were found. CONCLUSIONS: The CP mixture was shown to be an efficient tool for lowering plasma TRP in humans. The validity of this method with regard to behavioral changes remains to be established in healthy, vulnerable and clinical populations.

Cryptosporidium and Giardia in swimming pools in the Netherlands.

The occurrence of Cryptosporidium and Giardia in indoor swimming pools in the Netherlands was studied at five locations. The backwash water from seven pool filters was analysed for the presence of Cryptosporidium oocysts and Giardia cysts for a period of 1 year. Of the 153 samples of filter backwash water analysed, 18 (11.8%) were found positive for either Cryptosporidium (4.6%), Giardia (5.9%) or both (1.3%). Oocysts and cysts were also detected in the water of one toddler pool and one learner pool. Although most of the (oo)cysts in the filter backwash water were dead, viable and potentially infectious oocysts were detected in the learner pool. On the basis of numbers of potentially infectious (oo)cysts detected in the learner pool, and assuming one visit to an infected pool per year, risk assessment indicated an estimated risk of infection with Cryptosporidium that exceeded the generally accepted risk of one infection per 10,000 persons per year. Guidelines for pool operators on how to manage faecal accidents and public information on the importance of hygiene in swimming pool complexes are recommended tools in controlling the risk of infection.

Net fluxes of pesticides from the Scheldt Estuary into the North Sea: a model approach.

A hydrological model was constructed with the commercially available modelling environment ECoS for the calculation of mixing plots of dissolved pesticide concentrations in the Scheldt Estuary. The model was based on a one-dimensional advection-dispersion equation and dispersion coefficients were calculated from measured salinity profiles. The model could correctly predict the movement of water masses within the estuary. Nominal flushing times of the estuary were calculated with the fraction-of-freshwater method and ranged between 25 and 95 days, depending on the freshwater discharge. Model calculations demonstrated that the application-related time profiles of pesticide input may well induce curvature in the calculated estuarine mixing plot even if the pesticide behaves conservatively. Calculated mixing plots were compared with experimental data and good agreement was obtained between the measurements and the conservative mixing plot of atrazine. For metolachlor an additional direct emission had to be modelled to explain the differences between the experimental data and the conservative mixing plot. For dichlorvos and simazine. on the other hand, an estuarine loss constant had to be included in the model. Using a least-squares procedure the estuarine loss constants for dichlorvos and simazine were estimated at half-lives of five and 26 days, respectively. Because mixing plots were strongly influenced by the time profiles of pesticide input, standard procedures in which net fluxes are calculated from mixing plots, were not applicable. Therefore, net fluxes were calculated with a newly developed procedure in which the estuarine loss constants and the estuarine flushing time were combined. For the non-conservative compounds dichlorvos and simazine, the net fluxes to the North Sea were found to be 96 and 64%, respectively, lower than the gross fluxes transported by the River Scheldt.

Outer membrane composition of a lipopolysaccharide-deficient Neisseria meningitidis mutant.

In the pathogen Neisseria meningitidis, a completely lipopolysaccharide (LPS)-deficient but viable mutant can be obtained by insertional inactivation of the lpxA gene, encoding UDP-GlcNAc acyltransferase required for the first step of lipid A biosynthesis. To study how outer membrane structure and biogenesis are affected by the absence of this normally major component, inner and outer membranes were separated and their composition analysed. The expression and assembly of integral outer membrane proteins appeared largely unaffected. However, the expression of iron limitation-inducible, cell surface-exposed lipoproteins was greatly reduced. Major changes were seen in the phospholipid composition, with a shift towards phosphatidylethanolamine and phosphatidylglycerol species containing mostly shorter chain, saturated fatty acids, one of which was unique to the LPS-deficient outer membrane. The presence of the capsular polysaccharide turned out to be essential for viability without LPS, as demonstrated by using a strain in which LPS biosynthesis could be switched on or off through a tac promoter-controlled lpxA gene. Taken together, these results can help to explain why meningococci have the unique ability to survive without LPS.