Wädenswil, Switzerland
Wädenswil, Switzerland

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PubMed | ETH Zurich and Institute for Food science IFS
Type: Journal Article | Journal: FEMS microbiology letters | Year: 2016

In bacteria, cysteine can be synthesized from serine by two steps involving an L-serine O-acetyltransferase (SAT) and a cysteine synthase (CysK). While CysK is found in the publicly available annotated genome from Lactobacillus casei ATCC 334, a gene encoding SAT (cysE) is missing. In this study, we found that various strains of L. casei grew in a chemically defined medium containing sulfide as the sole sulfur source, indicating the presence of a serine O-acetyltransferase. The gene lying upstream of cysK is predicted to encode a homoserine trans-succinylase (metA). To study the function of this gene, it was cloned from L. casei FAM18110. The purified, recombinant protein did not acylate L-homoserine in vitro. Instead, it catalyzed the formation of O-acetyl serine from L-serine and acetyl-CoA. Furthermore, the plasmid expressing the L. casei gene complemented an Escherichia coli cysE mutant strain but not an E. coli metA mutant. This clearly demonstrated that the gene annotated as metA in fact encodes the SAT function and should be annotated as cysE.


PubMed | Lombardy and Emilia Romagna Experimental Zooprophylactic Institute, Lane College, Institute for Food science IFS and University of Milan
Type: Journal Article | Journal: Journal of food protection | Year: 2016

Quantitative microbial risk assessment (QMRA) models are extensively applied to inform management of a broad range of food safety risks. Inevitably, QMRA modeling involves an element of simplification of the biological process of interest. Two features that are frequently simplified or disregarded are the pathogenicity of multiple strains of a single pathogen and consumer behavior at the household level. In this study, we developed a QMRA model with a multiple-strain approach and a consumer phase module (CPM) based on uncertainty distributions fitted from field data. We modeled exposure to staphylococcal enterotoxin A in raw milk in Lombardy; a specific enterotoxin production module was thus included. The model is adaptable and could be used to assess the risk related to other pathogens in raw milk as well as other staphylococcal enterotoxins. The multiplestrain approach, implemented as a multinomial process, allowed the inclusion of variability and uncertainty with regard to pathogenicity at the bacterial level. Data from 301 questionnaires submitted to raw milk consumers were used to obtain uncertainty distributions for the CPM. The distributions were modeled to be easily updatable with further data or evidence. The sources of uncertainty due to the multiple-strain approach and the CPM were identified, and their impact on the output was assessed by comparing specific scenarios to the baseline. When the distributions reflecting the uncertainty in consumer behavior were fixed to the 95th percentile, the risk of exposure increased up to 160 times. This reflects the importance of taking into consideration the diversity of consumers habits at the household level and the impact that the lack of knowledge about variables in the CPM can have on the final QMRA estimates. The multiple-strain approach lends itself to use in other food matrices besides raw milk and allows the model to better capture the complexity of the real world and to be capable of geographical specificity.


PubMed | Institute for Food science IFS and University of Bern
Type: | Journal: European journal of preventive cardiology | Year: 2016

The aim of this study was to determine short-term effects of trans fatty acid (TFA) intake from ruminant and industrial sources on surrogate markers of cardiovascular risk in the context of a balanced diet with 30-36% of daily energy from fat.Prospective, randomized, double-blind, parallel-design study.In this study, 142 healthy volunteers aged 45 to 69 years were randomly allocated to three different diets: either a diet enriched with 2% of daily energy intake from ruminant TFA (rTFA) or with industrial TFA (iTFA), or a diet without TFA (wTFA), for a duration of four weeks. The primary outcome parameter was endothelial function measured by brachial artery flow mediated dilation (FMD). Secondary outcome parameters included biomarkers for inflammation, coagulation and endothelial function and lipid profiles. One hundred and twenty-nine participants completed the study.Neither alpine butter with TFA from ruminant source nor margarine with industrially produced TFA showed significant effects on brachial artery FMD (FMD% differences: rTFA vs. iTFA 0.04 (95% confidence interval 0.91 to 0.98), rTFA vs. wTFA -0.98 (-2.00 to 0.04) and iTFA vs. wTFA -1.04 (-2.38 to 0.30). With rTFA, there was a small but significant increase of total cholesterol: rTFA over wTFA 1.04 (1.00 to 1.07mmol/l) and LDL-cholesterol: rTFA over wTFA 1.08 (1.03 to 1.14mmol/l) without concomitant increase of biomarkers for inflammation or coagulation.Short-term intake of TFA at 2% of total daily energy intake from neither ruminant nor industrially produced sources does not have any negative impact on brachial artery FMD, inflammation and coagulation markers in healthy subjects.


Fuchsmann P.,Institute for Food science IFS | Stern M.T.,Institute for Food science IFS | Brugger Y.-A.,Institute for Food science IFS | Breme K.,Institute for Food science IFS
Journal of Agricultural and Food Chemistry | Year: 2015

To establish the odor profiles of three differently fabricated commercial Swiss Tilsit cheeses, analyses were conducted using headspace solid-phase microextraction gas chromatography-mass spectrometry/pulsed flame photometric detection and gas chromatography-olfactometry to identify and quantitate volatile compounds. In addition, odor quality and the impact of target sulfur compounds on the overall odor of the cheeses were investigated. The odor profile was found to be mainly influenced by buttery-cheesy and sulfury odor notes in all cheeses. Buttery-cheesy odor notes were attributed to three main molecules: butanoic acid, 3-methylbutanoic acid, and butane-2,3-dione. Over a dozen volatile sulfur compounds were detected at parts per billion levels, but only a few influenced the odor profile of the cheeses: methanethiol, dimethyl disulfide, bis(methylthio)methane, dimethyl trisulfide, 3-(methylthio)propanal, and 2-methyltetrahydrothiophen-3-one (tentative). In conclusion, the conducted analyses allowed differentiation of the cheeses, and gas chromatography-olfactometry results confirmed that partially thermized milk cheese has a more intense and more multifaceted overall flavor. © 2015 American Chemical Society.


Berger T.F.H.,Institute for Food science IFS | Luginbuhl W.,ChemStat
Accreditation and Quality Assurance | Year: 2016

The somatic cell count (SCC) of milk is one of the main indicators of the udder health status of lactating mammals and is a hygiene criterion of raw milk used to manufacture dairy products. An increase in SCC is regarded as one of the primary indicators of inflammation of the mammary gland. Therefore, SCC is relevant in food legislation as well as in the payment of ex-farm raw milk and it has a major impact on farm management and breeding programs. Its determination is one of the most frequently performed analytical tests worldwide. Routine measurements of SCC are almost exclusively done using automated fluoro-opto-electronic counting. However, certified reference materials for SCC are lacking, and the microscopic reference method is not reliable because of serious inherent weaknesses. A reference system approach may help to largely overcome these deficiencies and help to assure equivalence in SCC worldwide. The approach is characterised as a positioning system fed by different types of information from various sources. A statistical approach for comparing proficiency tests (PTs) by assessing them using a quality index PQ and assessing participating laboratories using a quality index PL, both deriving from probabilities, is proposed. The basic assumption is that PT schemes are conducted according to recognised guidelines in order to compute performance characteristics, such as z-scores, repeatability and reproducibility standard deviations. Standard deviations are compared with the method validation data from the ISO method. Input quantities close to or smaller than the reference data of the method validation or the assigned value of the PT result in values for PQ and PL close to the maximum value. Evaluation examples of well-known PTs show the practicability of the proposed approach. © 2016 The Author(s)


Remus-Emsermann M.N.P.,Institute for Food science IFS | Remus-Emsermann M.N.P.,University of Canterbury | Gisler P.,Institute for Food science IFS | Drissner D.,Institute for Food science IFS
FEMS Microbiology Letters | Year: 2016

Here we present the generation and function of two sets of bacterial plasmids that harbor fluorescent genes encoding either blue, cyan, yellow or red fluorescent proteins. In the first set, protein expression is controlled by the strong and constitutive nptII promoter whereas in the second set, the strong tac promoter was chosen that underlies LacIq regulation. Furthermore, the plasmids are mobilizable, contain Tn7 transposons and a temperature-sensitive origin of replication. Using Escherichia coli S17-1 as donor strain, the plasmids allow fast and convenient Tn7-transposon delivery into many enterobacterial hosts, such as the here-used E. coli O157:H7. This procedure omits the need of preparing competent recipient cells and antibiotic resistances are only transiently conferred to the recipients. As the fluorescence proteins show little to no overlap in fluorescence emission, the constructs are well suited for the study of multicolored synthetic bacterial communities during biofilm production or in host colonization studies, e.g. of plant surfaces. Furthermore, tac promoter-reporter constructs allow the generation of so-called reproductive success reporters, which allow to estimate past doublings of bacterial individuals after introduction into environments, emphasizing the role of individual cells during colonization. © FEMS 2016.


PubMed | University of Barcelona, Institute for Food science IFS and Swiss Institute of Bioinformatics
Type: Journal Article | Journal: Journal of dairy science | Year: 2016

Here we report the isolation of heat-resistant Escherichia coli from raw milk cheeses. Detection of the heat-resistance markers clpK and orfI by PCR was followed by phenotypical confirmation of increased heat-resistance. These strains were Shiga toxin-negative and, although several were found to be multidrug resistant, no plasmids encoding extended-spectrum -lactamases (ESBL) were found in any of the isolates. The aim of this study was to assess the potential of these strains to acquire ESBL plasmids and a modified Shiga toxin-encoding phage. Only 4 ESBL-encoding, heat-sensitive E. coli strains were isolated from 1,251 dairy samples (2/455 raw milk and 2/796 raw milk cheese samples). One incompatibility group FII plasmid (CTX-M-14, 79.0 kb) and 3 incompatibility group I1 plasmids (CTX-M-15, 95.2, 96.1, and 97.8 kb) were fully sequenced and de novo assembled. All 4 plasmids are readily transferred to heat-resistant E. coli isolates in plate matings (9.710


PubMed | Institute for Food science IFS
Type: Journal Article | Journal: Journal of agricultural and food chemistry | Year: 2015

To establish the odor profiles of three differently fabricated commercial Swiss Tilsit cheeses, analyses were conducted using headspace solid-phase microextraction gas chromatography-mass spectrometry/pulsed flame photometric detection and gas chromatography-olfactometry to identify and quantitate volatile compounds. In addition, odor quality and the impact of target sulfur compounds on the overall odor of the cheeses were investigated. The odor profile was found to be mainly influenced by buttery-cheesy and sulfury odor notes in all cheeses. Buttery-cheesy odor notes were attributed to three main molecules: butanoic acid, 3-methylbutanoic acid, and butane-2,3-dione. Over a dozen volatile sulfur compounds were detected at parts per billion levels, but only a few influenced the odor profile of the cheeses: methanethiol, dimethyl disulfide, bis(methylthio)methane, dimethyl trisulfide, 3-(methylthio)propanal, and 2-methyltetrahydrothiophen-3-one (tentative). In conclusion, the conducted analyses allowed differentiation of the cheeses, and gas chromatography-olfactometry results confirmed that partially thermized milk cheese has a more intense and more multifaceted overall flavor.


PubMed | Institute for Food science IFS
Type: | Journal: Journal of visualized experiments : JoVE | Year: 2016

The ribosomal spacer PCR (RS-PCR) is a highly resolving and robust genotyping method for S. aureus that allows a high throughput at moderate costs and is, therefore, suitable to be used for routine purposes. For best resolution, data evaluation and data management, a miniaturized electrophoresis system is required. Together with such an electrophoresis system and the in-house developed software (freely available here) assignment of the pattern of bands to a genotype is standardized and straight forward. DNA extraction is simple (boiling prep), setting-up of the reactions is easy and they can be run on any standard PCR machine. PCR cycling is common except prolonged ramping and elongation times. Compared to spa typing and Multi Locus Sequence Typing (MLST), RS-PCR does not require DNA sequencing what simplifies the analysis considerably and allows a high throughput. Furthermore, the resolution for bovine strains of S. aureus is at least as good as spa typing and better than MLST or pulsed-field gel electrophoresis (PFGE). The RS-PCR data base includes presently a total of 141 genotypes and variants. The method is highly associated with the virulence gene pattern, contagiosity and pathogenicity of S. aureus strains involved in bovine mastitis. S. aureus genotype B (GTB) is contagious and causes herds problems causing large costs in the Switzerland and other European countries. All the other genotypes observed in Switzerland infect individual cows and quarters. Genotyping by RS-PCR allows the reliable prediction of the epidemiological and the pathogenic potential of S. aureus involved in bovine intramammary infection (IMI), two key factors for clinical veterinary medicine. Because of these beneficial properties together with moderate costs and a high sample throughput the goal of this publication is to give a detailed, step-by-step protocol for easily establishing and running RS-PCR for genotyping S. aureus in other laboratories.


PubMed | Institute for Livestock science ILS and Institute for Food science IFS
Type: | Journal: Food microbiology | Year: 2016

Occasionally, melissopalynological analysis reveals the presence of bakers yeast (Saccharomyces cerevisiae) in honey sediments. A field experiment reproducing a common spring bee feeding practice, using sugar paste containing bakers yeast, was performed to understand how S.cerevisiae are introduced into honey. Apart from classical microscopy, a real-time quantitative PCR (qPCR) system specific for S.cerevisiae was established for quantification of S.cerevisiae in honeys. Results showed that S.cerevisiae cells are stored in the honey of the brood combs and are also transferred into honey in the supers. The concentrations of S.cerevisiae were highest in honey of the brood frames immediately after the feeding and decreased over time to low concentrations at the end of the year. A high content of S.cerevisiae cells were also found in the honey from supers of the spring harvest. Observed S.cerevisiae cells were not able to multiply in a high-sugar environment, such as honey, and their viability decreased rapidly after addition to the honey. The screening of 200 Swiss honeys revealed the presence of S.cerevisiae in 4.5% of the samples, as determined by microscopy and qPCR. Finally, the method described here may indicate an unwanted sucrose addition to honey through bee-feeding.

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