Tool-use in a blended undergraduate course: In Search of user profiles

The popularity of today’s blended courses in higher education is driven by the assumption that students are provided with a rich toolset that supports them in their learning process. However, little is known on how students actually use these tools and how this affects their performance for the course. The current study investigates how students use the entire toolset at their disposal, whether tool-use patterns can be found and if these patterns affect performance for the course. Logging students (n = 156) actions throughout the content management system and registering students’ use of the face-to-face support in an undergraduate course, the study reveals large student differences and an underuse for some tool-types. Further to this, K-means cluster analysis reveals three distinct tool-use patterns or user profiles: the no-users, the intensive users and the incoherent users. These patterns are characterized by different tool-choices and even different use intensity among students. Evidence is retrieved that these tool-use differences are problematic since multivariate analysis of variance reveals significant performance effects. Hence, these results imply that not all students seem to profit from the learning affordances that are provided. Similar as evidence in controlled settings, the results suggest that learner control in using tools cannot be taken for granted. Consequently, this study legitimates more research into the influencing (student and context) variables that can explain these differences.     

Molecular Methods in Food Safety Microbiology: Interpretation and Implications of Nucleic Acid Detection

Because of increasing demand for rapid results, molecular techniques are now applied for the detection of microorganisms in foodstuffs. However, interpretation problems can arise for the results generated by molecular methods in relation to the associated public health risk. Discrepancies between results obtained by molecular and conventional culture methods stem from the difference in target, namely nucleic acids instead of actively growing microorganisms. Nucleic acids constitute 5% to 15% of the dry weight of all living cells and are relatively stable, even after cell death, so they may be present in a food matrix after the foodborne microorganisms have been inactivated. Therefore, interpretation of the public health significance of positive results generated by nucleic acid detection methods warrants some additional consideration. This review discusses the stability of nucleic acids in general and highlights the persistence of microbial nucleic acids after diverse food‐processing techniques based on data from the scientific literature. Considerable amounts of DNA and RNA (intact or fragmented) persist after inactivation of bacteria and viruses by most of the commonly applied treatments in the food industry. An overview of the existing adaptations for molecular assays to cope with these problems is provided, including large fragment amplification, flotation, (enzymatic) pretreatment, and various binding assays. Finally, the negligible risks of ingesting free microbial nucleic acids are discussed and this review ends with the future perspectives of molecular methods such as next‐generation sequencing in diagnostic and source attribution food microbiology.     

Pre- and Postharvest Preventive Measures and Intervention Strategies to Control Microbial Food Safety Hazards of Fresh Leafy Vegetables

This review includes an overview of the most important preventive measures along the farm to fork chain to prevent microbial contamination of leafy greens. It also includes the technological and managerial interventions related to primary production, postharvest handling, processing practices, distribution, and consumer handling to eliminate pathogens in leafy greens. When the microbiological risk is already present, preventive measures to limit actual contamination events or pathogen survival are considered intervention strategies. In codes of practice the focus is mainly put on explaining preventive measures. However, it is also important to establish more focused intervention strategies. This review is centered mainly on leafy vegetables as the commodity identified as the highest priority in terms of fresh produce microbial safety from a global perspective. There is no unique preventive measure or intervention strategy that could be applied at one point of the food chain. We should encourage growers of leafy greens to establish procedures based on the HACCP principles at the level of primary production. The traceability of leafy vegetables along the chain is an essential element in ensuring food safety. Thus, in dealing with the food safety issues associated with fresh produce it is clear that a multidisciplinary farm to fork strategy is required.     

Modification of the bile salts-Irgasan-brilliant green agar for enumeration of Aeromonas species from food

The present study evaluated the productivity of BIBG medium for the isolation of Aeromonas spp. from food and describes a modification of the BIBG medium (mBIBG) (increased pH (8.7), replacement of xylose by soluble starch as a carbon source, decreased concentration of bile salts) to increase its selectivity and electivity. Using the mBIBG medium, growth of the majority of the Enterobacteriaceae (9/10) was suppressed except for Citrobacter freundii. The mBIBG medium supported growth of Pseudomonas species but a clear distinction between Aeromonas and Pseudomonas colonies could be made. Interpretation of the mBIBG medium should be performed after 24 h of incubation. It was noted that three of the 27 Aeromonas strains tested did not develop on the mBIBG medium. The ability or inability to grow on a selective medium is strain-dependent. Enumeration of Aeromonas species (A. hydrophila LMG 3771, A. caviae LMG 3775, A. veronii biovar veronii LMG 9075, A. veronii biovar sobria LMG 13071) from artificially contaminated foods (shrimp, minced meat (beef/pork), precut leek, and shredded carrots) confirmed that the mBIBG medium is suitable for quantitative recovery of aeromonads (ca. 10(2)-10(7) cfu/g) in the presence of a high background flora (10(5)-10(6) cfu/g). Screening of naturally contaminated foods (vegetables, seafood, meat) for the presence of Aeromonas resulted in three out of 14 food samples showing presumptive Aeromonas colonies on mBIBG.     

The use of immuno-magnetic separation (IMS) as a tool in a sample preparation method for direct detection of L. monocytogenes in cheese

A sample preparation procedure was developed for direct detection of L. monocytogenes in cheese. The sample preparation protocol consisted of a 10-fold dilution and homogenization, a centrifugation step to precipitate large food particles, passage of the supernatant over a sieve and through a separatory funnel to further eliminate food particles and fat, a centrifugation step to recover the bacterial pellet and finally enzymatic digestion of the suspension to degrade the remaining small food particles. Recovery of L. monocytogenes was confirmed by plating on Oxford medium and confirmation of suspected colonies. This protocol enabled direct detection (without prior enrichment) of low numbers of L. monocytogenes (0.5-1.5 cfu/g cheese) from different types of cheese. The performance of Dynabeads Anti-Listeria (Dynal, Oslo, Norway) for selective recovery of L. monocytogenes and their applicability in the above mentioned procedure for direct detection of low numbers of L. monocytogenes from cheese was evaluated. IMS could not separate and recover L. monocytogenes from the food particles in the concentrated suspension. The use of IMS after a 24 h enrichment procedure (as recommended by the manufacturer) allowed for the detection of low numbers of L. monocytogenes (< 10 cfu/g). However, experiments in broth cultures showed that although the detection limit of IMS with Dynabeads Anti-Listeria was 40-100 cfu/ml, the ratio of L. monocytogenes to non-Listeria flora was not increased. Thus, selective enrichment or concentration of L. monocytogenes was not obtained.     

PCR assay for detection of the E. coli O157:H7 eae-gene and effect of the sample preparation method on PCR detection of heat-killed E. coli O157:H7 in ground beef

A PCR assay targeting the 3' end of the eae-gene of E. coli O157:H7 has been developed. It was shown to be specific for the E. coli O157:H7 eae-gene. Sensitivity of the PCR assay was 1 pg DNA or 10(3) cfu per PCR reaction. Subsequently, a study was conducted to examine the effect of the food matrix and the sample preparation method on PCR detection of non-viable cells using heat-killed E. coli O157:H7 in ground beef as a model system. Inoculated ground beef samples were subjected to either selective enrichment or immediately prepared for PCR analysis. Four sample preparation methods were applied: centrifugation, buoyant density centrifugation (BDC), immunomagnetic separation (IMS), and chelex extraction. Production of false-positive results due to amplification of the DNA of dead cells occurred if the number of heat-killed cells exceeded 10(8) cfu/g. For inocula <10(8) cfu/g, PCR results for heat- killed E. coli O157:H7 cells depended upon the sample preparation method. It was shown that the inclusion of two washings steps of the bacterial pellet before DNA extraction was the critical factor for elimination of false-positive results due to heat-killed cells in the centrifugation and BDC procedure. IMS did not produce false-positive results due to heat-killed cells (two washing steps were included in the IMS procedure). With the chelex-extraction method, false-positive results due to heat-killed cells were obtained. An effect of the ground beef food matrix on the presence of amplifiable DNA was noted.     

Critical evaluation of the EU-technical guidance on shelf-life studies for L. monocytogenes on RTE-foods: a case study for smoked salmon

In November 2008, a technical guidance document on the challenge test protocol was published by the EU CRL (Community of Reference Laboratory) for L. monocytogenes. This document describes the practical aspects on the execution of a challenge test in order to comply to the EU Commission regulation N° 2073/2005 on microbiological criteria for foodstuff. In this guideline two approaches are specified. On the one hand challenge tests, based on actual data measurements at the beginning and end of the shelf-life of products stored under reasonably foreseen T-profile, are described. On the other hand, growth potential is calculated by predictive models using a validated maximum specific growth rate.The present study evaluates the two above mentioned approaches on cold smoked salmon, a typical risk product for L. monocytogenes. The focus is on: (i) the relative importance of intrabatch versus interbatch variability, (ii) the concept of a simple challenge test based on actual data at start and end of shelf life versus a modelling approach and (iii) the interpretation of challenge tests. Next to this, available tertiary models were used to estimate the growth potential of these products based on their initial physicochemical characteristics.From the results it could be concluded that in some batches considerable intrabatch variability was obtained. In general, however, the interbatch variability was significantly higher than intrabatch variability. Concerning the two above mentioned methods for challenge tests, it can be stated that the first approach (simple challenge test) can be set up rather rapidly and is cost-effective for SMEs (small and medium enterprises) but provides only a single isolated outcome. This implies that challenge tests should be redone if changes occur in composition or production process. The second (modelling) approach, using extended challenge tests to establish growth parameters needs larger set ups and more complicated data analysis, which makes them more expensive. Using available tertiary models has the major advantage that the most important intrinsic and extrinsic factors can be included for the prediction of the growth parameter. It was clear that product specific models, taking into account the interaction effects with background flora, performed the best. Regarding the challenge tests, it can be concluded that the best approach to choose will depend on the particular context as in the end both approaches will lead to the same conclusion.     

Fate of Foodborne Viruses in the “Farm to Fork” Chain of Fresh Produce

Norovirus (NoV) and hepatitis A virus (HAV) are the most important foodborne viruses. Fresh produce has been identified as an important vehicle for their transmission. In order to supply a basis to identify possible prevention and control strategies, this review intends to demonstrate the fate of foodborne viruses in the farm to fork chain of fresh produce, which include the introduction routes (contamination sources), the viral survival abilities at different stages, and the reactions of foodborne viruses towards the treatments used in food processing of fresh produce. In general, the preharvest contamination comes mainly from soli fertilizer or irrigation water, while the harvest and postharvest contaminations come mainly from food handlers, which can be both symptomatic and asymptomatic. Foodborne viruses show high stabilities in all the stages of fresh produce production and processing. Low‐temperature storage and other currently used preservation techniques, as well as washing by water have shown limited added value for reducing the virus load on fresh produce. Chemical sanitizers, although with limitations, are strongly recommended to be applied in the wash water in order to minimize cross‐contamination. Alternatively, radiation strategies have shown promising inactivating effects on foodborne viruses. For high‐pressure processing and thermal treatment, efforts have to be made on setting up treatment parameters to induce sufficient viral inactivation within a food matrix and to protect the sensory and nutritional qualities of fresh produce to the largest extent.     

Impact of intestinal microbiota and gastrointestinal conditions on the in vitro survival and growth of Bacillus cereus

Ingestion of B. cereus can result in diarrhea, if these bacteria survive gastrointestinal passage and achieve growth and enterotoxin production in the small intestine. The gastrointestinal survival of vegetative cells and spores of the diarrheal food poisoning strain B. cereus NVH 1230-88 was investigated during in vitro batch experiments simulating the stomach, duodenum and ileum using simulation media and competing intestinal microbiota. All spores and approx. 30% of the vegetative B. cereus cells survived the 2 h incubation in gastric medium with pH 4.0. Sterile intestinal medium induced germination of spores and enabled outgrowth of vegetative cells to approx. 7 log CFU/mL. The behavior of B. cereus in the intestinal environment with competing intestinal bacteria was determined by their relative concentrations. Besides the numbers of intestinal bacteria, the nutrition and composition of the intestinal community were also very important for the growth inhibition of B. cereus.