Ulrike Zitz | University of Natural Resources and Life Sciences, Vienna (BOKU) (original) (raw)

Papers by Ulrike Zitz

International Journal of Food Microbiology, Nov 1, 2007

There is urgent need for having available suitable methods and data regarding the susceptibility ... more There is urgent need for having available suitable methods and data regarding the susceptibility levels of antibiotic resistant and sensitive strains of bifidobacteria. Based on a defined standard operation procedure, agar disc diffusion and broth microdilution were compared in order to evaluate the antimicrobial susceptibility profiles of 82 B. pseudolongum and 80 B. thermophilum strains mainly originating from the meat production chain. The methods that were assessed showed interpretable agreement within this study. The disc diffusion zone diameters are highly reproducible making the method a useful alternative to broth microdilution for antimicrobial susceptibility screening of bifidobacteria.

Applied sciences, Jan 14, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Animal, 2020

Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fib... more Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fiber compound for monogastric animals. The aim of this study was to evaluate the influence of native or fermented WB on the gut physiology and microbiology of laying hens. To accomplish this, 24 laying hens were fed the following diets: conventional diet without WB; 15% native WB in the diet; 15% WB fermented with Pleurotus eryngii; and 15% WB fermented with P. eryngii and a lactic acid bacterial culture. Immediately after slaughtering, digesta samples were taken from the jejunum, ileum and cecum, respectively. Total DNA was extracted and subsequently investigated with 16S DNA amplicon sequencing. Neither native nor fermented WB supplementations negatively affected the feed conversion ratio, laying performance or the relative abundances and alpha-diversity of microbiota in the intestine. Effects of WB-based diets on gut morphology were only recognized in the jejunum (reduced villum height and mucosa thickness). Likewise, WB supplementation decreased the digestibility of DM and starch. Based on these findings, it was demonstrated that different WB variants are applicable without exerting practically negative consequences on performance or on gut microbiota. Fermentation improved the digestibility/retention of dietary fat and phosphorus. However, no further beneficial effects were observed. This study also allowed a more in-depth view on the laying hens' gut microbiome and its variation within the gut segments.

Lebensmittel-Wissenschaft & Technologie, Dec 1, 2017

Wheat bran, a side product of the milling industry, can serve as valuable food component, feed in... more Wheat bran, a side product of the milling industry, can serve as valuable food component, feed ingredient or feedstock for biorefineries. However, all these applications bear drawbacks of sensory, physiological and technological challenges. The present study investigates an alternative utilization strategy of wheat bran as substrate for mushroom production and evaluates residual substrates for further sustainable application possibilities. Substrates containing 250 g/kg, 500 g/kg and 980 g/kg of wheat bran were inoculated with spores of Pleurotus eryngii and Pleurotus ostreatus followed by solid-state fermentation. Highest biomass yield, protein content and dry matter were obtained on 980 g/kg of bran when inoculated with Pleurotus eryngii. Beyond that, fermentation also markedly decreased the phytate content, the viscosity and the neutral detergent fiber level in this substrate. Furthermore, the substrate containing 980 g/kg bran displayed a remarkable decrease in neutral detergent fiber. Pleurotus fungi production on wheat bran leads to improved edible mushroom quality compared to commonly used substrates and also offers some innovative application possibilities of the fermented substrate in animal feeding.

Journal of Food Protection, Aug 1, 2011

Recent foodborne crises have demonstrated the importance of monitoring food safety. In terms of m... more Recent foodborne crises have demonstrated the importance of monitoring food safety. In terms of microbiological criteria, food safety requires the reliable detection of pathogens such as Listeria monocytogenes along the food chain by appropriate analytical methods. However, indications exist that accompanying Listeria innocua strains suppress the growth of L. monocytogenes during selective enrichment, which may cause reduced or even inhibited detection. To study these effects, the limit of detection of L. monocytogenes was investigated in the presence of L. innocua using the International Organization for Standardization standard method ISO 11290-1 and the VIDAS LDUO system, an automated method based on enzyme-linked fluorescence technology. The challenge was to provide low initial Listeria concentrations at sufficient precision to quantify the influence on the probability of detection of L. monocytogenes. The application of reference materials appropriate for quantitative test methods and a standardized dilution procedure were necessary to ensure accurate CFU levels of defined proportions of mixtures of both Listeria species. During selective enrichment, overgrowth of L. monocytogenes by L. innocua could be confirmed, leading to high rates of false-negative results. Moreover, with both methods, a significant decrease in the detectability of L. monocytogenes could be quantified at ratios of 2:1 at very low concentrations representative of natural contamination levels often found in foods and environments. It is concluded that there is a need to improve existing procedures with respect to selective enrichment, as well as the detection techniques.

International Dairy Journal, Oct 1, 2017

Abstract In cheese production, knowledge of clostridial spore levels in milk is crucial to avoid ... more Abstract In cheese production, knowledge of clostridial spore levels in milk is crucial to avoid economic losses due to late-blowing, a characteristic quality defect observed especially in hard cheeses. However, no international standard method is available to quantify clostridial spores in milk. Since performance data on the currently applied enumeration methods have not been systematically investigated, in this study we assessed four routine media and most probable number (MPN) methods for the enumeration of cheese-damaging clostridia in milk. Among the four evaluated methods, statistically significant differences became evident, while moderate to optimal correlations were observed. Bacterial isolates from positive reactions were identified using molecular methods. All four methods assessed showed a severe lack of selectivity due to the incorporation of non-clostridial spore-formers in the counts produced. The results illustrate major drawbacks of currently used methods and stress the necessity for improving method selectivity, sensitivity and reliability before standardisation can be envisaged.

Poultry Science, Apr 1, 2019

The increase in antibiotic resistance is a global concern for human and animal health. Resistant ... more The increase in antibiotic resistance is a global concern for human and animal health. Resistant microorganisms can spread between food-producing animals and humans. The objective of this review was to identify the type and amount of antibiotics used in poultry production and the level of antibiotic resistance in Escherichia coli isolated from broilers. Isolate information was obtained from national monitoring programs and research studies conducted in large poultryproducing regions: US, China, Brazil, and countries of EU-Poland, United Kingdom, Germany, France, and Spain. The survey results clearly display the absence of a harmonized approach in the monitoring of antibiotics per animal species and the evaluation of resistances using the same methodology. There is no public long-term quantitative data available targeting the amount of antibiotics used in poultry, with the exception of France. Data on antibiotic-resistant E. coli are available for most regions but detection of resistance and number of isolates in each study differs among regions; therefore, statistical evaluation was not possible. Data from France indicate that the decreased use of tetracyclines leads to a reduction in the detected resistance rates. The fluoroquinolones, third-generation cephalosporins, macrolides, and polymyxins ("highest priority critically important" antibiotics for human medicine according to WHO) are approved for use in large poultry-producing regions, with the exception of fluoroquinolones in the US and cephalosporins in the EU. The approval of cephalosporins in China could not be evaluated. Tetracyclines, aminoglycosides, sulfonamides, and penicillins are registered for use in poultry in all evaluated countries. The average resistance rates in E. coli to representatives of these antibiotic classes are higher than 40% in all countries, with the exception of ampicillin in the US. The resistance rates to fluoroquinolones and quinolones in the US, where fluoroquinolones are not registered for use, are below 5%, while the average of resistant E. coli is above 40% in Brazil, China, and EU, where use of fluoroquinolones is legalized. However, banning of fluoroquinolones and quinolones has not totally eliminated the occurrence of resistant populations.

Bodenkultur, Dec 1, 2018

A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wh... more A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wheat bran (WB) and two vegetable oils on digestibility and retention. In addition, two different adaption times were evaluated. The following treatments were applied: no WB/29 g/kg rapeseed oil, no WB/29 g/kg sunflower oil, 75 g/kg WB/45 g/kg rapeseed oil, 75 g/kg WB/45 g/kg sunflower oil, 150 g/kg WB/62 g/kg rapeseed oil, and 150 g/kg WB/62 g/kg sunflower oil. Samples of excrements were examined for dry matter, crude protein, ether extracts, starch, neutral detergent fiber, short-chain fatty acids, and elemental analyses. The effect of the adaption time showed a significantly negative effect on the digestibility of NDF and the retention of phosphorus when a longer prefeeding period was applied. Furthermore, the results demonstrate that regardless of high dietary fiber content, laying hens are capable of tolerating higher dietary fiber levels compared to the fiber level of corn soybean meal diets. Precondition is a balanced nutrient content between diets. Therefore, wheat bran supplementation can be regarded as an interesting option for a sustainable utilization of by-products to produce food of animal origin.

Journal of the Science of Food and Agriculture, Apr 14, 2011

In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated p... more In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated pressed sugar beet pulp silages was investigated. Hop beta acids are natural substances which display their effect at low concentrations. Fresh pressed beet pulp material was mixed with soil to artificially contaminate it with clostridia. Laboratory silos were filled with the substrate, stored at 25 °C and opened for sampling at 0, 2, 8, 15, 30, 60, and 90 days. The impact on clostridial growth during silage fermentation was monitored by determination of the pH value and dry matter content, as well as chemical analysis of the fermentation products. Throughout the experiments, the effect of a commercial silage inoculant based on lactic acid bacteria (LAB) and hop-resistant LAB were examined with and without the combination of plant-based antimicrobials. Results indicate that in contaminated silage samples without any additives high butyric acid contents occurred due to clostridial growth. This spoilage could not be suppressed by the application of LAB, whereas the combined application of LAB and hop beta acids significantly improved silage quality, which was reflected by favourable organic acid composition (P < 0.05). The experimental data indicate that the application of hop beta acids improves the preservation effect of LAB in suppressing clostridial growth in silages and thus demonstrates some potential for the combined use of plant-based antimicrobials and LAB.

Microorganisms, May 19, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of the Science of Food and Agriculture, Apr 14, 2011

In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated p... more In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated pressed sugar beet pulp silages was investigated. Hop beta acids are natural substances which display their effect at low concentrations. Fresh pressed beet pulp material was mixed with soil to artificially contaminate it with clostridia. Laboratory silos were filled with the substrate, stored at 25 °C and opened for sampling at 0, 2, 8, 15, 30, 60, and 90 days. The impact on clostridial growth during silage fermentation was monitored by determination of the pH value and dry matter content, as well as chemical analysis of the fermentation products. Throughout the experiments, the effect of a commercial silage inoculant based on lactic acid bacteria (LAB) and hop-resistant LAB were examined with and without the combination of plant-based antimicrobials. Results indicate that in contaminated silage samples without any additives high butyric acid contents occurred due to clostridial growth. This spoilage could not be suppressed by the application of LAB, whereas the combined application of LAB and hop beta acids significantly improved silage quality, which was reflected by favourable organic acid composition (P < 0.05). The experimental data indicate that the application of hop beta acids improves the preservation effect of LAB in suppressing clostridial growth in silages and thus demonstrates some potential for the combined use of plant-based antimicrobials and LAB.

Applied and Environmental Microbiology, Jun 15, 2008

In recent years, the absence of acquired antimicrobial resistance has become an important criteri... more In recent years, the absence of acquired antimicrobial resistance has become an important criterion to evaluate the biosafety of lactobacilli used as industrial starter or probiotic cultures. At present, however, standards for susceptibility testing of Lactobacillus strains or approved guidelines for interpreting the test results are not available. Hence, this study was carried out to contribute to the establishment of a standardized procedure for antimicrobial susceptibility testing of lactobacilli. The results obtained by testing 104 strains of the Lactobacillus acidophilus group were compared based on broth microdilution, disk diffusion, and Etest. Except for some specific agent-related effects, agreement between MICs resulting from the broth microdilution method and the Etest was good. In addition, inhibition zone diameters determined with disk diffusion correlated well with MICs from Etest and broth microdilution.

Food Control, Apr 1, 2015

Food packaging materials fundamentally contribute to food quality and safety, as they protect the... more Food packaging materials fundamentally contribute to food quality and safety, as they protect the packaged food against external influences. In this context, the determination of the hygiene status of the packaging material is of great importance. However, European legislation neither sets any microbiological criteria nor provides any approved standard for the microbiological testing of food packaging materials. Nevertheless, reliable routine control is essential for guaranteeing high hygienic quality of packagings. With the aim to achieve a maximum recovery rate at low contamination levels, an improved experimental design was developed for the enumeration of the total colony count, yeasts and molds and Enterobacteriaceae on the surface of roll stock packaging materials. For this purpose, two different types of paper laminates were selected and exemplarily used as objects of investigation. Moreover, the performance of different growth media was compared for each microbiological parameter. This approach was followed by method validation using a selection of quantitative reference materials of representative microorganisms, including resistant forms of microbes such as bacterial endospores and fungal spores.

Animal, 2020

Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fib... more Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fiber compound for monogastric animals. The aim of this study was to evaluate the influence of native or fermented WB on the gut physiology and microbiology of laying hens. To accomplish this, 24 laying hens were fed the following diets: conventional diet without WB; 15% native WB in the diet; 15% WB fermented with Pleurotus eryngii; and 15% WB fermented with P. eryngii and a lactic acid bacterial culture. Immediately after slaughtering, digesta samples were taken from the jejunum, ileum and cecum, respectively. Total DNA was extracted and subsequently investigated with 16S DNA amplicon sequencing. Neither native nor fermented WB supplementations negatively affected the feed conversion ratio, laying performance or the relative abundances and alpha-diversity of microbiota in the intestine. Effects of WB-based diets on gut morphology were only recognized in the jejunum (reduced villum height ...

Microorganisms

Butyric acid producing clostridia (BAPC) cause the so-called late-blowing defect, a serious quali... more Butyric acid producing clostridia (BAPC) cause the so-called late-blowing defect, a serious quality problem in semi-hard and hard cheeses. Late-blown cheeses are characterized by undesired slits and cracks, irregular eyes, and off-flavors due to excessive amounts of gas and organic acids produced by clostridia. Clostridial transfer to raw milk can occur during milking through dirty teats. Therefore, teat cleaning before milking is a key factor in preventing clostridial contamination of the milk. However, different cleaning methods are used, and little information is available on the efficacy of routine teat cleaning in reducing clostridial endospores. The main objectives of this study were to assess the extent of udder contamination with BAPC spores and to investigate the efficacy of routine teat cleaning on BAPC spore counts in milk. In a longitudinal study, eight dairy farms were visited during five sampling events. Clostridial spore counts were quantified from teat skin before an...

Foods, 2020

Naturally fermented foods are an important part of the typical diet in Cambodia. However, the foo... more Naturally fermented foods are an important part of the typical diet in Cambodia. However, the food safety status of these products has not been widely studied. The aim of this study was, therefore, to provide an overview of the quality of these foods in relation to microbiology and biogenic amines. Additionally, the obtained results were compared to the habits and practices of Cambodians in handling this type of food. A total of 57 fermented foods (42 fishery and 15 vegetable products) were collected from different retail markets in the capital of Cambodia. Pathogenic Salmonella spp., Listeria spp., and Listeria monocytogenes were not detected in 25 g samples. Generally, less than 102 cfu/g of Staphylococcus aureus, Escherichia coli, Pseudomonas spp., Enterobacteriaceae, and molds were present in the fermented foods. Bacillus cereus group members (<102 to 2.3 × 104 cfu/g), lactic acid bacteria (<102 to 1.1 × 107 cfu/g), halophilic and halotolerant bacteria (<102 to 8.9 × 10...

Journal of the Science of Food and Agriculture, 2020

BACKGROUND During the manufacture of sucrose from sugar beet, different microorganisms originatin... more BACKGROUND During the manufacture of sucrose from sugar beet, different microorganisms originating from the plant material as well as from the soil enter the process. Due to the formation of polysaccharide-based slimes, these contaminants may induce several adverse effects such as filtration problems during juice purification. In addition, certain microorganisms metabolize sucrose leading to product losses encompassing financial consequences. To better understand and to prevent these negative effects, the aim of the study was to investigate the evolution of relevant bacterial groups including their metabolites appearing during the extraction process. For this purpose, one production cycle was monitored to identify the major contamination steps and to clarify how they relate to the processing conditions. Traditionally, different antimicrobial agents such as formaldehyde, sulphur dioxide, hypochlorous acid, sodium hypochlorite and chlorine dioxide have been added to inhibit microbial growth. In the present study, a rosin-based product derived from pine trees was applied as an alternative to the aforementioned substances. RESULTS According to the findings, press water, raw juice and mid-tower juice were identified as being highly contaminated with bacteria, and processing conditions such as time, temperature and pH level significantly influenced bacterial levels and corresponding metabolites. Among the contaminants identified, lactic acid bacteria, mesophilic and thermophilic aerobic bacteria played some dominant role, whereas lactic acid, acetic acid, butyric acid and ethanol were identified as typical metabolites. CONCLUSION Bacterial growth during production could be reduced by shock-dosing of the rosin-based material in the extraction area. This article is protected by copyright. All rights reserved.

Die Bodenkultur: Journal of Land Management, Food and Environment, 2018

Summary A feeding trial with laying hens was conducted to study the effect of rising levels of di... more Summary A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wheat bran (WB) and two vegetable oils on digestibility and retention. In addition, two different adaption times were evaluated. The following treatments were applied: no WB/29 g/kg rapeseed oil, no WB/29 g/kg sunflower oil, 75 g/kg WB/45 g/kg rapeseed oil, 75 g/kg WB/45 g/kg sunflower oil, 150 g/kg WB/62 g/kg rapeseed oil, and 150 g/kg WB/62 g/kg sunflower oil. Samples of excrements were examined for dry matter, crude protein, ether extracts, starch, neutral detergent fiber, short-chain fatty acids, and elemental analyses. The effect of the adaption time showed a significantly negative effect on the digestibility of NDF and the retention of phosphorus when a longer prefeeding period was applied. Furthermore, the results demonstrate that regardless of high dietary fiber content, laying hens are capable of tolerating higher dietary fiber levels compared to the fiber level of corn so...

Agricultural Sciences, 2018

Wheat bran (WB) is an important side product of the milling industry and plays an increasing role... more Wheat bran (WB) is an important side product of the milling industry and plays an increasing role in animal feeding. Despite its nutritional value, its application is limited as a result of its pronounced fiber content. Taking into account the potential use of WB supplementation in feed for laying hens thereby replacing human edible foodstuffs, the influence of different WB levels (0 g•kg −1 , 75 g•kg −1 , and 150 g•kg −1) combined with sunflower or rapeseed oil on egg quality was studied. Among the egg-related quality parameters investigated, eggshell cleanliness, shell rigidity, egg weight, haugh units, yolk and albumen mass, color, pH value, dry matter, crude protein, crude ash, fatty acid spectrum, cholesterol and α-tocopherol of the yolk were monitored. No negative effect of WB supplementation was observed in terms of egg weight, shell weight, albumen weight, yolk weight, haugh unit, shell thickness and eggshell breaking strength. However, certain parameters (i.e. α-tocopherol content, Σn−3 PUFA) were enhanced by feeding 75 g•kg −1 and 150 g•kg −1 WB. The use of WB (75 g•kg −1 and 150 g•kg −1) had no negative effect on egg quality and can, therefore, be recommended for laying hen diets up to 150 g•kg −1. Additionally, the application of rapeseed oil high in Σn−3 PUFA resulted in yolks exhibiting a low Σn−6 PUFA/Σn−3 PUFA ratio.

International Journal of Food Microbiology, Nov 1, 2007

There is urgent need for having available suitable methods and data regarding the susceptibility ... more There is urgent need for having available suitable methods and data regarding the susceptibility levels of antibiotic resistant and sensitive strains of bifidobacteria. Based on a defined standard operation procedure, agar disc diffusion and broth microdilution were compared in order to evaluate the antimicrobial susceptibility profiles of 82 B. pseudolongum and 80 B. thermophilum strains mainly originating from the meat production chain. The methods that were assessed showed interpretable agreement within this study. The disc diffusion zone diameters are highly reproducible making the method a useful alternative to broth microdilution for antimicrobial susceptibility screening of bifidobacteria.

Applied sciences, Jan 14, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Animal, 2020

Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fib... more Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fiber compound for monogastric animals. The aim of this study was to evaluate the influence of native or fermented WB on the gut physiology and microbiology of laying hens. To accomplish this, 24 laying hens were fed the following diets: conventional diet without WB; 15% native WB in the diet; 15% WB fermented with Pleurotus eryngii; and 15% WB fermented with P. eryngii and a lactic acid bacterial culture. Immediately after slaughtering, digesta samples were taken from the jejunum, ileum and cecum, respectively. Total DNA was extracted and subsequently investigated with 16S DNA amplicon sequencing. Neither native nor fermented WB supplementations negatively affected the feed conversion ratio, laying performance or the relative abundances and alpha-diversity of microbiota in the intestine. Effects of WB-based diets on gut morphology were only recognized in the jejunum (reduced villum height and mucosa thickness). Likewise, WB supplementation decreased the digestibility of DM and starch. Based on these findings, it was demonstrated that different WB variants are applicable without exerting practically negative consequences on performance or on gut microbiota. Fermentation improved the digestibility/retention of dietary fat and phosphorus. However, no further beneficial effects were observed. This study also allowed a more in-depth view on the laying hens' gut microbiome and its variation within the gut segments.

Lebensmittel-Wissenschaft & Technologie, Dec 1, 2017

Wheat bran, a side product of the milling industry, can serve as valuable food component, feed in... more Wheat bran, a side product of the milling industry, can serve as valuable food component, feed ingredient or feedstock for biorefineries. However, all these applications bear drawbacks of sensory, physiological and technological challenges. The present study investigates an alternative utilization strategy of wheat bran as substrate for mushroom production and evaluates residual substrates for further sustainable application possibilities. Substrates containing 250 g/kg, 500 g/kg and 980 g/kg of wheat bran were inoculated with spores of Pleurotus eryngii and Pleurotus ostreatus followed by solid-state fermentation. Highest biomass yield, protein content and dry matter were obtained on 980 g/kg of bran when inoculated with Pleurotus eryngii. Beyond that, fermentation also markedly decreased the phytate content, the viscosity and the neutral detergent fiber level in this substrate. Furthermore, the substrate containing 980 g/kg bran displayed a remarkable decrease in neutral detergent fiber. Pleurotus fungi production on wheat bran leads to improved edible mushroom quality compared to commonly used substrates and also offers some innovative application possibilities of the fermented substrate in animal feeding.

Journal of Food Protection, Aug 1, 2011

Recent foodborne crises have demonstrated the importance of monitoring food safety. In terms of m... more Recent foodborne crises have demonstrated the importance of monitoring food safety. In terms of microbiological criteria, food safety requires the reliable detection of pathogens such as Listeria monocytogenes along the food chain by appropriate analytical methods. However, indications exist that accompanying Listeria innocua strains suppress the growth of L. monocytogenes during selective enrichment, which may cause reduced or even inhibited detection. To study these effects, the limit of detection of L. monocytogenes was investigated in the presence of L. innocua using the International Organization for Standardization standard method ISO 11290-1 and the VIDAS LDUO system, an automated method based on enzyme-linked fluorescence technology. The challenge was to provide low initial Listeria concentrations at sufficient precision to quantify the influence on the probability of detection of L. monocytogenes. The application of reference materials appropriate for quantitative test methods and a standardized dilution procedure were necessary to ensure accurate CFU levels of defined proportions of mixtures of both Listeria species. During selective enrichment, overgrowth of L. monocytogenes by L. innocua could be confirmed, leading to high rates of false-negative results. Moreover, with both methods, a significant decrease in the detectability of L. monocytogenes could be quantified at ratios of 2:1 at very low concentrations representative of natural contamination levels often found in foods and environments. It is concluded that there is a need to improve existing procedures with respect to selective enrichment, as well as the detection techniques.

International Dairy Journal, Oct 1, 2017

Abstract In cheese production, knowledge of clostridial spore levels in milk is crucial to avoid ... more Abstract In cheese production, knowledge of clostridial spore levels in milk is crucial to avoid economic losses due to late-blowing, a characteristic quality defect observed especially in hard cheeses. However, no international standard method is available to quantify clostridial spores in milk. Since performance data on the currently applied enumeration methods have not been systematically investigated, in this study we assessed four routine media and most probable number (MPN) methods for the enumeration of cheese-damaging clostridia in milk. Among the four evaluated methods, statistically significant differences became evident, while moderate to optimal correlations were observed. Bacterial isolates from positive reactions were identified using molecular methods. All four methods assessed showed a severe lack of selectivity due to the incorporation of non-clostridial spore-formers in the counts produced. The results illustrate major drawbacks of currently used methods and stress the necessity for improving method selectivity, sensitivity and reliability before standardisation can be envisaged.

Poultry Science, Apr 1, 2019

The increase in antibiotic resistance is a global concern for human and animal health. Resistant ... more The increase in antibiotic resistance is a global concern for human and animal health. Resistant microorganisms can spread between food-producing animals and humans. The objective of this review was to identify the type and amount of antibiotics used in poultry production and the level of antibiotic resistance in Escherichia coli isolated from broilers. Isolate information was obtained from national monitoring programs and research studies conducted in large poultryproducing regions: US, China, Brazil, and countries of EU-Poland, United Kingdom, Germany, France, and Spain. The survey results clearly display the absence of a harmonized approach in the monitoring of antibiotics per animal species and the evaluation of resistances using the same methodology. There is no public long-term quantitative data available targeting the amount of antibiotics used in poultry, with the exception of France. Data on antibiotic-resistant E. coli are available for most regions but detection of resistance and number of isolates in each study differs among regions; therefore, statistical evaluation was not possible. Data from France indicate that the decreased use of tetracyclines leads to a reduction in the detected resistance rates. The fluoroquinolones, third-generation cephalosporins, macrolides, and polymyxins ("highest priority critically important" antibiotics for human medicine according to WHO) are approved for use in large poultry-producing regions, with the exception of fluoroquinolones in the US and cephalosporins in the EU. The approval of cephalosporins in China could not be evaluated. Tetracyclines, aminoglycosides, sulfonamides, and penicillins are registered for use in poultry in all evaluated countries. The average resistance rates in E. coli to representatives of these antibiotic classes are higher than 40% in all countries, with the exception of ampicillin in the US. The resistance rates to fluoroquinolones and quinolones in the US, where fluoroquinolones are not registered for use, are below 5%, while the average of resistant E. coli is above 40% in Brazil, China, and EU, where use of fluoroquinolones is legalized. However, banning of fluoroquinolones and quinolones has not totally eliminated the occurrence of resistant populations.

Bodenkultur, Dec 1, 2018

A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wh... more A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wheat bran (WB) and two vegetable oils on digestibility and retention. In addition, two different adaption times were evaluated. The following treatments were applied: no WB/29 g/kg rapeseed oil, no WB/29 g/kg sunflower oil, 75 g/kg WB/45 g/kg rapeseed oil, 75 g/kg WB/45 g/kg sunflower oil, 150 g/kg WB/62 g/kg rapeseed oil, and 150 g/kg WB/62 g/kg sunflower oil. Samples of excrements were examined for dry matter, crude protein, ether extracts, starch, neutral detergent fiber, short-chain fatty acids, and elemental analyses. The effect of the adaption time showed a significantly negative effect on the digestibility of NDF and the retention of phosphorus when a longer prefeeding period was applied. Furthermore, the results demonstrate that regardless of high dietary fiber content, laying hens are capable of tolerating higher dietary fiber levels compared to the fiber level of corn soybean meal diets. Precondition is a balanced nutrient content between diets. Therefore, wheat bran supplementation can be regarded as an interesting option for a sustainable utilization of by-products to produce food of animal origin.

Journal of the Science of Food and Agriculture, Apr 14, 2011

In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated p... more In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated pressed sugar beet pulp silages was investigated. Hop beta acids are natural substances which display their effect at low concentrations. Fresh pressed beet pulp material was mixed with soil to artificially contaminate it with clostridia. Laboratory silos were filled with the substrate, stored at 25 °C and opened for sampling at 0, 2, 8, 15, 30, 60, and 90 days. The impact on clostridial growth during silage fermentation was monitored by determination of the pH value and dry matter content, as well as chemical analysis of the fermentation products. Throughout the experiments, the effect of a commercial silage inoculant based on lactic acid bacteria (LAB) and hop-resistant LAB were examined with and without the combination of plant-based antimicrobials. Results indicate that in contaminated silage samples without any additives high butyric acid contents occurred due to clostridial growth. This spoilage could not be suppressed by the application of LAB, whereas the combined application of LAB and hop beta acids significantly improved silage quality, which was reflected by favourable organic acid composition (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05). The experimental data indicate that the application of hop beta acids improves the preservation effect of LAB in suppressing clostridial growth in silages and thus demonstrates some potential for the combined use of plant-based antimicrobials and LAB.

Microorganisms, May 19, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of the Science of Food and Agriculture, Apr 14, 2011

In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated p... more In this study the inhibition of hop beta acids on the growth of clostridia in soil-contaminated pressed sugar beet pulp silages was investigated. Hop beta acids are natural substances which display their effect at low concentrations. Fresh pressed beet pulp material was mixed with soil to artificially contaminate it with clostridia. Laboratory silos were filled with the substrate, stored at 25 °C and opened for sampling at 0, 2, 8, 15, 30, 60, and 90 days. The impact on clostridial growth during silage fermentation was monitored by determination of the pH value and dry matter content, as well as chemical analysis of the fermentation products. Throughout the experiments, the effect of a commercial silage inoculant based on lactic acid bacteria (LAB) and hop-resistant LAB were examined with and without the combination of plant-based antimicrobials. Results indicate that in contaminated silage samples without any additives high butyric acid contents occurred due to clostridial growth. This spoilage could not be suppressed by the application of LAB, whereas the combined application of LAB and hop beta acids significantly improved silage quality, which was reflected by favourable organic acid composition (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05). The experimental data indicate that the application of hop beta acids improves the preservation effect of LAB in suppressing clostridial growth in silages and thus demonstrates some potential for the combined use of plant-based antimicrobials and LAB.

Applied and Environmental Microbiology, Jun 15, 2008

In recent years, the absence of acquired antimicrobial resistance has become an important criteri... more In recent years, the absence of acquired antimicrobial resistance has become an important criterion to evaluate the biosafety of lactobacilli used as industrial starter or probiotic cultures. At present, however, standards for susceptibility testing of Lactobacillus strains or approved guidelines for interpreting the test results are not available. Hence, this study was carried out to contribute to the establishment of a standardized procedure for antimicrobial susceptibility testing of lactobacilli. The results obtained by testing 104 strains of the Lactobacillus acidophilus group were compared based on broth microdilution, disk diffusion, and Etest. Except for some specific agent-related effects, agreement between MICs resulting from the broth microdilution method and the Etest was good. In addition, inhibition zone diameters determined with disk diffusion correlated well with MICs from Etest and broth microdilution.

Food Control, Apr 1, 2015

Food packaging materials fundamentally contribute to food quality and safety, as they protect the... more Food packaging materials fundamentally contribute to food quality and safety, as they protect the packaged food against external influences. In this context, the determination of the hygiene status of the packaging material is of great importance. However, European legislation neither sets any microbiological criteria nor provides any approved standard for the microbiological testing of food packaging materials. Nevertheless, reliable routine control is essential for guaranteeing high hygienic quality of packagings. With the aim to achieve a maximum recovery rate at low contamination levels, an improved experimental design was developed for the enumeration of the total colony count, yeasts and molds and Enterobacteriaceae on the surface of roll stock packaging materials. For this purpose, two different types of paper laminates were selected and exemplarily used as objects of investigation. Moreover, the performance of different growth media was compared for each microbiological parameter. This approach was followed by method validation using a selection of quantitative reference materials of representative microorganisms, including resistant forms of microbes such as bacterial endospores and fungal spores.

Animal, 2020

Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fib... more Wheat bran (WB) is an important side product of the milling industry and can serve as dietary fiber compound for monogastric animals. The aim of this study was to evaluate the influence of native or fermented WB on the gut physiology and microbiology of laying hens. To accomplish this, 24 laying hens were fed the following diets: conventional diet without WB; 15% native WB in the diet; 15% WB fermented with Pleurotus eryngii; and 15% WB fermented with P. eryngii and a lactic acid bacterial culture. Immediately after slaughtering, digesta samples were taken from the jejunum, ileum and cecum, respectively. Total DNA was extracted and subsequently investigated with 16S DNA amplicon sequencing. Neither native nor fermented WB supplementations negatively affected the feed conversion ratio, laying performance or the relative abundances and alpha-diversity of microbiota in the intestine. Effects of WB-based diets on gut morphology were only recognized in the jejunum (reduced villum height ...

Microorganisms

Butyric acid producing clostridia (BAPC) cause the so-called late-blowing defect, a serious quali... more Butyric acid producing clostridia (BAPC) cause the so-called late-blowing defect, a serious quality problem in semi-hard and hard cheeses. Late-blown cheeses are characterized by undesired slits and cracks, irregular eyes, and off-flavors due to excessive amounts of gas and organic acids produced by clostridia. Clostridial transfer to raw milk can occur during milking through dirty teats. Therefore, teat cleaning before milking is a key factor in preventing clostridial contamination of the milk. However, different cleaning methods are used, and little information is available on the efficacy of routine teat cleaning in reducing clostridial endospores. The main objectives of this study were to assess the extent of udder contamination with BAPC spores and to investigate the efficacy of routine teat cleaning on BAPC spore counts in milk. In a longitudinal study, eight dairy farms were visited during five sampling events. Clostridial spore counts were quantified from teat skin before an...

Foods, 2020

Naturally fermented foods are an important part of the typical diet in Cambodia. However, the foo... more Naturally fermented foods are an important part of the typical diet in Cambodia. However, the food safety status of these products has not been widely studied. The aim of this study was, therefore, to provide an overview of the quality of these foods in relation to microbiology and biogenic amines. Additionally, the obtained results were compared to the habits and practices of Cambodians in handling this type of food. A total of 57 fermented foods (42 fishery and 15 vegetable products) were collected from different retail markets in the capital of Cambodia. Pathogenic Salmonella spp., Listeria spp., and Listeria monocytogenes were not detected in 25 g samples. Generally, less than 102 cfu/g of Staphylococcus aureus, Escherichia coli, Pseudomonas spp., Enterobacteriaceae, and molds were present in the fermented foods. Bacillus cereus group members (<102 to 2.3 × 104 cfu/g), lactic acid bacteria (<102 to 1.1 × 107 cfu/g), halophilic and halotolerant bacteria (<102 to 8.9 × 10...

Journal of the Science of Food and Agriculture, 2020

BACKGROUND During the manufacture of sucrose from sugar beet, different microorganisms originatin... more BACKGROUND During the manufacture of sucrose from sugar beet, different microorganisms originating from the plant material as well as from the soil enter the process. Due to the formation of polysaccharide-based slimes, these contaminants may induce several adverse effects such as filtration problems during juice purification. In addition, certain microorganisms metabolize sucrose leading to product losses encompassing financial consequences. To better understand and to prevent these negative effects, the aim of the study was to investigate the evolution of relevant bacterial groups including their metabolites appearing during the extraction process. For this purpose, one production cycle was monitored to identify the major contamination steps and to clarify how they relate to the processing conditions. Traditionally, different antimicrobial agents such as formaldehyde, sulphur dioxide, hypochlorous acid, sodium hypochlorite and chlorine dioxide have been added to inhibit microbial growth. In the present study, a rosin-based product derived from pine trees was applied as an alternative to the aforementioned substances. RESULTS According to the findings, press water, raw juice and mid-tower juice were identified as being highly contaminated with bacteria, and processing conditions such as time, temperature and pH level significantly influenced bacterial levels and corresponding metabolites. Among the contaminants identified, lactic acid bacteria, mesophilic and thermophilic aerobic bacteria played some dominant role, whereas lactic acid, acetic acid, butyric acid and ethanol were identified as typical metabolites. CONCLUSION Bacterial growth during production could be reduced by shock-dosing of the rosin-based material in the extraction area. This article is protected by copyright. All rights reserved.

Die Bodenkultur: Journal of Land Management, Food and Environment, 2018

Summary A feeding trial with laying hens was conducted to study the effect of rising levels of di... more Summary A feeding trial with laying hens was conducted to study the effect of rising levels of dietary wheat bran (WB) and two vegetable oils on digestibility and retention. In addition, two different adaption times were evaluated. The following treatments were applied: no WB/29 g/kg rapeseed oil, no WB/29 g/kg sunflower oil, 75 g/kg WB/45 g/kg rapeseed oil, 75 g/kg WB/45 g/kg sunflower oil, 150 g/kg WB/62 g/kg rapeseed oil, and 150 g/kg WB/62 g/kg sunflower oil. Samples of excrements were examined for dry matter, crude protein, ether extracts, starch, neutral detergent fiber, short-chain fatty acids, and elemental analyses. The effect of the adaption time showed a significantly negative effect on the digestibility of NDF and the retention of phosphorus when a longer prefeeding period was applied. Furthermore, the results demonstrate that regardless of high dietary fiber content, laying hens are capable of tolerating higher dietary fiber levels compared to the fiber level of corn so...

Agricultural Sciences, 2018

Wheat bran (WB) is an important side product of the milling industry and plays an increasing role... more Wheat bran (WB) is an important side product of the milling industry and plays an increasing role in animal feeding. Despite its nutritional value, its application is limited as a result of its pronounced fiber content. Taking into account the potential use of WB supplementation in feed for laying hens thereby replacing human edible foodstuffs, the influence of different WB levels (0 g•kg −1 , 75 g•kg −1 , and 150 g•kg −1) combined with sunflower or rapeseed oil on egg quality was studied. Among the egg-related quality parameters investigated, eggshell cleanliness, shell rigidity, egg weight, haugh units, yolk and albumen mass, color, pH value, dry matter, crude protein, crude ash, fatty acid spectrum, cholesterol and α-tocopherol of the yolk were monitored. No negative effect of WB supplementation was observed in terms of egg weight, shell weight, albumen weight, yolk weight, haugh unit, shell thickness and eggshell breaking strength. However, certain parameters (i.e. α-tocopherol content, Σn−3 PUFA) were enhanced by feeding 75 g•kg −1 and 150 g•kg −1 WB. The use of WB (75 g•kg −1 and 150 g•kg −1) had no negative effect on egg quality and can, therefore, be recommended for laying hen diets up to 150 g•kg −1. Additionally, the application of rapeseed oil high in Σn−3 PUFA resulted in yolks exhibiting a low Σn−6 PUFA/Σn−3 PUFA ratio.