Showing papers in "Food Microbiology in 2015"
TL;DR: The sensory impact of the VOCs and their dynamics during storage is discussed to highlight their possible contribution to the spoilage of meat.
Abstract: Microbial spoilage of meat is a complex event to which many different bacterial populations can contribute depending on the temperature of storage and packaging conditions. The spoilage can derive from microbial development and consumption of meat nutrients by bacteria with a consequent release of undesired metabolites. The volatile organic compounds (VOCs) that are generated during meat storage can have an olfactory impact and can lead to rejection of the product when their concentration increase significantly as a result of microbial development. The VOCs most commonly identified in meat during storage include alcohols, aldehydes, ketones, fatty acids, esters and sulfur compounds. In this review, the VOCs found in fresh meat during storage in specific conditions are described together with the possible bacterial populations responsible of their production. In addition, on the basis of the data available in the literature, the sensory impact of the VOCs and their dynamics during storage is discussed to highlight their possible contribution to the spoilage of meat.
TL;DR: The present review focuses on the principal mechanisms involved in the formation of biofilms of food-borne pathogens, where biofilm behaviour is driven by its three-dimensional heterogeneity and by species interactions within these biostructures, and the authors look at some emergent control strategies.
Abstract: Microbial life abounds on surfaces in both natural and industrial environments, one of which is the food industry. A solid substrate, water and some nutrients are sufficient to allow the construction of a microbial fortress, a so-called biofilm. Survival strategies developed by these surface-associated ecosystems are beginning to be deciphered in the context of rudimentary laboratory biofilms. Gelatinous organic matrices consisting of complex mixtures of self-produced biopolymers ensure the cohesion of these biological structures and contribute to their resistance and persistence. Moreover, far from being just simple three-dimensional assemblies of identical cells, biofilms are composed of heterogeneous sub-populations with distinctive behaviours that contribute to their global ecological success. In the clinical field, biofilm-associated infections (BAI) are known to trigger chronic infections that require dedicated therapies. A similar belief emerging in the food industry, where biofilm tolerance to environmental stresses, including cleaning and disinfection/sanitation, can result in the persistence of bacterial pathogens and the recurrent cross-contamination of food products. The present review focuses on the principal mechanisms involved in the formation of biofilms of food-borne pathogens, where biofilm behaviour is driven by its three-dimensional heterogeneity and by species interactions within these biostructures, and we look at some emergent control strategies.
TL;DR: A fundamental understanding of Campylobacter is provided, critical for improved diagnosis, surveillance and control of foodborne bacterial infection and human infection.
Abstract: Despite over 30 years of research, campylobacteriosis is the most prevalent foodborne bacterial infection in many countries including in the European Union and the United States of America. However, relatively little is known about the virulence factors in Campylobacter or how an apparently fragile organism can survive in the food chain, often with enhanced pathogenicity. This review collates information on the virulence and survival determinants including motility, chemotaxis, adhesion, invasion, multidrug resistance, bile resistance and stress response factors. It discusses their function in transition through the food processing environment and human infection. In doing so it provides a fundamental understanding of Campylobacter, critical for improved diagnosis, surveillance and control.
TL;DR: It is shown that multiple modes of action may explain as M. pulcherrima provide excellent control of postharvest botrytis bunch rot of grape, and shows the highest biocontrol in vitro activity.
Abstract: Strains belonging to the species Saccharomyces cerevisiae, Wickerhamomyces anomalus, Metschnikowia pulcherrima and Aureobasidium pullulans, isolated from different food sources, were tested in vitro as biocontrol agents (BCAs) against the post-harvest pathogenic mold Botrytis cinerea. All yeast strains demonstrated antifungal activity at different levels depending on species and medium. Killer strains of W. anomalus and S. cerevisiae showed the highest biocontrol in vitro activity, as demonstrated by largest inhibition halos. The competition for iron and the ability to form biofilm and to colonize fruit wounds were hypothesized as the main action mechanisms for M. pulcherrima. The production of hydrolytic enzymes and the ability to colonize the wounds were the most important mechanisms for biocontrol activity in A. pullulans and W. anomalus, which also showed high ability to form biofilm. The production of volatile organic compounds (VOCs) with in vitro and in vivo inhibitory effect on pathogen growth was observed for the species W. anomalus, S. cerevisiae and M. pulcherrima. Our study clearly indicates that multiple modes of action may explain as M. pulcherrima provide excellent control of postharvest botrytis bunch rot of grape.
TL;DR: Oregano oil nanoemulsions were formulated with a food-grade emulsifier and evaluated for their efficacy in inactivating the growth of foodborne bacteria on fresh lettuce and Scanning Electron Microscopy demonstrated disrupted bacterial membranes due to the oreganoOil treatment.
Abstract: Although antimicrobial activities of plant essential oils are well documented, challenges remain as to their application in fresh produce due to the hydrophobic nature of essential oils. Oregano oil nanoemulsions were formulated with a food-grade emulsifier and evaluated for their efficacy in inactivating the growth of foodborne bacteria on fresh lettuce. Lettuce was artificially inoculated with Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli O157:H7, followed by a one-minute dipping in oregano oil nanoemulsions (0.05% or 0.1%). Samples were stored at 4 °C and enumerated for bacteria at fixed intervals (0 h, 3 h, 24 h, and 72 h). Compared to control, 0.05% nanoemulsion showed an up to 3.44, 2.31, and 3.05 log CFU/g reductions in L. monocytogenes, S. Typhimurium, and E. coli O157:H7, respectively. Up to 3.57, 3.26, and 3.35 log CFU/g reductions were observed on the same bacteria by the 0.1% treatment. Scanning Electron Microscopy (SEM) demonstrated disrupted bacterial membranes due to the oregano oil treatment. The data suggest that applying oregano oil nanoemulsions to fresh produce may be an effective antimicrobial control strategy.
TL;DR: Blueberries treated with cold plasma can inactivate microorganisms on blueberries and could be optimized to improve the safety and quality of produce.
Abstract: Cold plasma (CP) is a novel nonthermal technology, potentially useful in food processing settings. Berries were treated with atmospheric CP for 0, 15, 30, 45, 60, 90, or 120 s at a working distance of 7.5 cm with a mixture of 4 cubic feet/minute (cfm) of CP jet and 7 cfm of ambient air. Blueberries were sampled for total aerobic plate count (APC) and yeast/molds immediately after treatment and at 1, 2, and 7 days. Blueberries were also analyzed for compression firmness, surface color, and total anthocyanins immediately after each treatment. All treatments with CP significantly ( P L * and a * values and 45 s for the b * values. CP can inactivate microorganisms on blueberries and could be optimized to improve the safety and quality of produce.
TL;DR: This thin-layer DBD-plasma system can be applied to inactivate foodborne pathogens and cause minor deterioration of meat quality, which might be prevented by the use of hurdle technology.
Abstract: The effects of a flexible thin-layer dielectric barrier discharge (DBD) plasma system using a sealed package on microbial inactivation and quality attributes of fresh pork and beef were tested. Following a 10-min treatment, the microbial-load reductions of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium were 2.04, 2.54, and 2.68 Log CFU/g in pork-butt samples and 1.90, 2.57, and 2.58 Log CFU/g in beef-loin samples, respectively. Colorimetric analysis showed that DBD-plasma treatment did not significantly affect L* values (lightness) of pork and beef samples, but lowered a* values (redness) significantly after 5- and 7.5-min exposures. The plasma treatment significantly influenced lipid oxidation only after a 10-min exposure. The texture of both types of meat was unaffected by plasma treatment. All sensory parameters of treated and non-treated samples were comparable except for taste, which was negatively influenced by the plasma treatment (P < 0.05). This thin-layer DBD-plasma system can be applied to inactivate foodborne pathogens. The observed minor deterioration of meat quality might be prevented by the use of hurdle technology.
TL;DR: The aim of this study was to elucidate the bacteria and yeast species occurring in milk kefir grains collected in some Italian regions by combining the results of scanning electron microscopy analysis, viable counts on selective culture media, PCR-DGGE and pyrosequencing.
Abstract: Kefir grains are a unique symbiotic association of different microrganisms, mainly lactic acid bacteria, yeasts and occasionally acetic acid bacteria, cohabiting in a natural polysaccharide and a protein matrix. The microbial composition of kefir grains can be considered as extremely variable since it is strongly influenced by the geographical origin of the grains and by the sub-culturing method used. The aim of this study was to elucidate the bacteria and yeast species occurring in milk kefir grains collected in some Italian regions by combining the results of scanning electron microscopy analysis, viable counts on selective culture media, PCR-DGGE and pyrosequencing. The main bacterial species found was Lactobacillus kefiranofaciens while Dekkera anomala was the predominant yeast. The presence of sub-dominant species ascribed to Streptococcus thermophilus, Lactococcus lactis and Acetobacter genera was also highlighted. In addition, Lc. lactis, Enterococcus sp., Bacillus sp., Acetobacter fabarum, Acetobacter lovaniensis and Acetobacter orientalis were identified as part of the cultivable community. This work further confirms both the importance of combining culture-independent and culture-dependent approaches to study microbial diversity in food and how the combination of multiple 16S rRNA gene targets strengthens taxonomic identification using sequence-based identification approaches.
TL;DR: Investigating the bacterial diversity in batches of Salame Piacentino PDO, a dry fermented sausage that is typical of a regional area of Northern Italy, confirmed the presence of main bacterial species involved in the fermentation of salami as assessed by PCR-DGGE, but with a greater extent of resolution and quantitative assessments that are not possible by the mere analyses of gel banding patterns.
Abstract: The bacterial diversity involved in food fermentations is one of the most important factors shaping the final characteristics of traditional foods. Knowledge about this diversity can be greatly improved by the application of high-throughput sequencing technologies (HTS) coupled to the PCR amplification of the 16S rRNA subunit. Here we investigated the bacterial diversity in batches of Salame Piacentino PDO (Protected Designation of Origin), a dry fermented sausage that is typical of a regional area of Northern Italy. Salami samples from 6 different local factories were analysed at 0, 21, 49 and 63 days of ripening; raw meat at time 0 and casing samples at 21 days of ripening where also analysed, and the effect of starter addition was included in the experimental set-up. Culture-based microbiological analyses and PCR-DGGE were carried out in order to be compared with HTS results. A total of 722,196 high quality sequences were obtained after trimming, paired-reads assembly and quality screening of raw reads obtained by Illumina MiSeq sequencing of the two bacterial 16S hypervariable regions V3 and V4; manual curation of 16S database allowed a correct taxonomical classification at the species for 99.5% of these reads. Results confirmed the presence of main bacterial species involved in the fermentation of salami as assessed by PCR-DGGE, but with a greater extent of resolution and quantitative assessments that are not possible by the mere analyses of gel banding patterns. Thirty-two different Staphylococcus and 33 Lactobacillus species where identified in the salami from different producers, while the whole data set obtained accounted for 13 main families and 98 rare ones, 23 of which were present in at least 10% of the investigated samples, with casings being the major sources of the observed diversity. Multivariate analyses also showed that batches from 6 local producers tend to cluster altogether after 21 days of ripening, thus indicating that HTS has the potential for fine scale differentiation of local fermented foods.
TL;DR: It is demonstrated that phenolics metabolism may confer a selective advantage for lactobacilli in vegetable and fruit fermentation, and the metabolic routes are strongly dependent on the intrinsic factors of substrate.
Abstract: This study aimed to investigate the metabolism of phenolic acids and flavonoids during lactic acid fermentation of cherry juice and broccoli puree for potential food and pharmaceutical purposes. When fermenting cherry juice and broccoli puree, Lactobacillus spp. exhibited strain-specific metabolism of phenolic acid derivatives. The metabolism of protocatechuic, caffeic and p-coumaric acids through phenolic acid decarboxylases and reductases differed between mMRS and cherry juice and broccoli puree. The synthesis of reduced compounds was the highest during food fermentations and the substrate seemed to modulate the metabolism of phenolic compounds. The reduction of phenolic acids involves a hydrogen donor and the re-oxidation of the reduced co-factor NADH, which may provide a metabolic advantage through NAD(+) regeneration. Quinic acid reduction may replace fructose and pyruvate as hydrogen acceptors, and it may provide an energetic advantage to heterofermentative bacteria when growing in broccoli puree lacking of fructose. This study demonstrated that phenolics metabolism may confer a selective advantage for lactobacilli in vegetable and fruit fermentation, and the metabolic routes are strongly dependent on the intrinsic factors of substrate. Fermented cherry juice and broccoli puree, due to the selected bacterial bioconversion pathways, are enriched in phenolic derivative with high human bioavailability and biological activity.
TL;DR: This review lists the main bacterial species identified as food spoilers, their ability to develop during storage and/or processing, and the functions potentially involved in spoilage, and compiled an inventory of the available genome sequences of species encompassing spoilage strains.
Abstract: Most food products are highly perishable as they constitute a rich nutrient source for microbial development. Among the microorganisms contaminating food, some present metabolic activities leading to spoilage. In addition to hygienic rules to reduce contamination, various treatments are applied during production and storage to avoid the growth of unwanted microbes. The nature and appearance of spoilage therefore depend on the physiological state of spoilers and on their ability to resist the processing/storage conditions and flourish on the food matrix. Spoilage also relies on the interactions between the microorganisms composing the ecosystems encountered in food. The recent rapid increase in publicly available bacterial genome sequences, as well as the access to high-throughput methods, should lead to a better understanding of spoiler behavior and to the possibility of decreasing food spoilage. This review lists the main bacterial species identified as food spoilers, their ability to develop during storage and/or processing, and the functions potentially involved in spoilage. We have also compiled an inventory of the available genome sequences of species encompassing spoilage strains. Combining in silico analysis of genome sequences with experimental data is proposed in order to understand and thus control the bacterial spoilage of food better.
TL;DR: This review discusses the classification of L. lactis and the problems that arise with phenotype/genotype designation, the adaptation of non-dairy lactococci to milk, the traits associated with this adaptation and the potential application ofnon-d dairy lactitisci to dairy fermentations.
Abstract: Lactococcus lactis is an organism of substantial economic importance, used extensively in the production of fermented foods and widely held to have evolved from plant strains. The domestication of this organism to the milk environment is associated with genome reduction and gene decay, and the acquisition of specific genes involved in protein and lactose utilisation by horizontal gene transfer. In recent years, numerous studies have focused on uncovering the physiology and molecular biology of lactococcal strains from the wider environment for exploitation in the dairy industry. This in turn has facilitated comparative genome analysis of lactococci from different environments and provided insight into the natural phenotypic and genetic diversity of L. lactis. This diversity may be exploited in dairy fermentations to develop products with improved quality and sensory attributes. In this review, we discuss the classification of L. lactis and the problems that arise with phenotype/genotype designation. We also discuss the adaptation of non-dairy lactococci to milk, the traits associated with this adaptation and the potential application of non-dairy lactococci to dairy fermentations.
TL;DR: In natural apple Juice, the combination of US + 60 s PL at the highest temperature build-up was the most effective treatment for both strains, and in commercial apple juice, US did not contribute to further inactivation of spores, but significantly reduced yeast population.
Abstract: The aim of this study was to evaluate the effect of ultrasound (US) (600 W, 20 kHz and 95.2 μm wave amplitude; 10 or 30 min at 20, 30 or 44 ± 1 °C) and pulsed light (PL) (Xenon lamp; 3 pulses/s; 0.1 m distance; 2.4 J/cm(2)-71.6 J/cm(2); initial temperature 2, 30, 44 ± 1 °C) on the inactivation of Alicyclobacillus acidoterrestris ATCC 49025 spores and Saccharomyces cerevisiae KE162 inoculated in commercial (pH: 3.5; 12.5 °Brix) and natural squeezed (pH: 3.4; 11.8 °Brix) apple juices. Inactivation depended on treatment time, temperature, microorganism and matrix. Combination of these technologies led up to 3.0 log cycles of spore reduction in commercial apple juice and 2.0 log cycles in natural juice; while for S. cerevisiae, 6.4 and 5.8 log cycles of reduction were achieved in commercial and natural apple juices, respectively. In natural apple juice, the combination of US + 60 s PL at the highest temperature build-up (56 ± 1 °C) was the most effective treatment for both strains. In commercial apple juice, US did not contribute to further inactivation of spores, but significantly reduced yeast population. Certain combinations of US + PL kept on good microbial stability under refrigerated conditions for 15 days.
TL;DR: The newly developed encapsulated DBD-plasma system for use in a container can be applied to improve the safety of sliced cheese, and increasing post-treatment storage time can greatly enhance the system's pathogen-inactivation efficiency.
Abstract: Pathogen inactivation induced by atmospheric pressure dielectric barrier discharge (DBD) (250 W, 15 kHz, air discharge) produced in a rectangular plastic container and the effect of post-treatment storage time on inactivation were evaluated using agar plates and cheese slices. When agar plates were treated with plasma, populations of Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes showed 3.57, 6.69, and 6.53 decimal reductions at 60 s, 45 s, and 7 min, respectively. When the pathogens tested were inoculated on cheese slices, 2.67, 3.10, and 1.65 decimal reductions were achieved at the same respective treatment times. The post-treatment storage duration following plasma treatment potently affected further reduction in pathogen populations. Therefore, the newly developed encapsulated DBD-plasma system for use in a container can be applied to improve the safety of sliced cheese, and increasing post-treatment storage time can greatly enhance the system's pathogen-inactivation efficiency.
TL;DR: This review highlights recent advances in the understanding of the underlying molecular mechanisms of biofilm formation, the factors that regulate biofilm development and the role of quorum sensing andBiofilm formation in the virulence of foodborne pathogens.
Abstract: Seafood forms a part of a healthy diet. However, seafood can be contaminated with foodborne pathogens, resulting in disease outbreaks. Because people consume large amounts of seafood, such disease outbreaks are increasing worldwide. Seafood contamination is largely due to the naturally occurring phenomenon of biofilm formation. The common seafood bacterial pathogens that form biofilms are Vibrio spp., Aeromonas hydrophila, Salmonella spp., and Listeria monocytogenes. As these organisms pose a global health threat, recent research has focused on elucidating methods to eliminate these biofilm-forming bacteria from seafood, thereby improving food hygiene. Therefore, we highlight recent advances in our understanding of the underlying molecular mechanisms of biofilm formation, the factors that regulate biofilm development and the role of quorum sensing and biofilm formation in the virulence of foodborne pathogens. Currently, several novel methods have been successfully developed for controlling biofilms present in seafood. In this review, we also discuss the epidemiology of seafood-related diseases and the novel methods that could be used for future control of biofilm formation in seafood.
TL;DR: The traditional CSIs such as TVB-N and TMA-N were increased substantially only at the late stages of storage or after rejection of the products, making them unsuitable for freshness/spoilage monitoring throughout storage.
Abstract: Microbiological, sensory, TVB-N and TMA-N changes and Volatile Organic Compounds (VOCs) detection using the SPME/GC–MS technique, were performed to evaluate potential chemical spoilage indices (CSI) of gutted sea bass (Dicentrarchus labrax) stored at 2 °C under air and in modified atmosphere packaging (MAP CO2: 60%, O2: 10%, N2: 30%). Shelf-life, determined by sensory evaluation, of gutted sea bass stored at 2 °C under air and MAP was 9 and 13 d respectively. Pseudomonas and H2S producing bacteria were among the dominant spoilage microorganisms under both storage conditions, while Lactic Acid Bacteria (LAB) and Brochothrix thermosphacta were co-dominant with Pseudomonas and H2S producing bacteria under MAP. The traditional CSIs such as TVB-N and TMA-N were increased substantially only at the late stages of storage or after rejection of the products, making them unsuitable for freshness/spoilage monitoring throughout storage. A substantial number of VOCs attributed to microbiological action or chemical activity, were detected including alcohols, aldehydes, ketones, organic acids and esters. The level of microbial origin VOCs such as ethanol, 2-ethyl-1-hexanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 3-methylbutanal, 2-methylbutanal and some ethyl esters increased during storage, suggesting their potential as CSIs.
TL;DR: Microwave-powered cold plasma treatment was evaluated as a means to improve the microbiological safety of fresh vegetables and dried fruits and the Weibull model adequately described the inactivation of L. monocytogenes on cabbage by CPT.
Abstract: Microwave-powered cold plasma treatment (CPT) was evaluated as a means to improve the microbiological safety of fresh vegetables and dried fruits. The CPT at 900 W, conducted for 10 min using nitrogen as a plasma-forming gas, inactivated Salmonella Typhimurium inoculated on cabbage and lettuce by approximately 1.5 log CFU/g. The CPT at 400–900 W and 667 Pa, conducted for 1–10 min using a helium–oxygen gas mixture, inactivated Listeria monocytogenes on cabbage by 0.3–2.1 log CFU/g in a time-dependent manner (P
TL;DR: Results indicated that applying the Lactobacillus plantarum strains CIT3 and V7B3 to apples and lettuce, respectively, increased both the safety and shelf-life and combining the selected strains with natural antimicrobials produced a further increase in the shelf- life of these products without detrimental effects on the organoleptic qualities.
Abstract: Outbreaks of food-borne disease associated with the consumption of fresh and minimally processed fruits and vegetables have increased dramatically over the last few years. Traditional chemical sanitizers are unable to completely eradicate or kill the microorganisms on fresh produce. These conditions have stimulated research to alternative methods for increasing food safety. The use of protective cultures, particularly lactic acid bacteria (LAB), has been proposed for minimally processed products. However, the application of bioprotective cultures has been limited at the industrial level. From this perspective, the main aims of this study were to select LAB from minimally processed fruits and vegetables to be used as biocontrol agents and then to evaluate the effects of the selected strains, alone or in combination with natural antimicrobials (2-(E)-hexenal/hexanal, 2-(E)-hexenal/citral for apples and thyme for lamb's lettuce), on the shelf-life and safety characteristics of minimally processed apples and lamb's lettuce. The results indicated that applying the Lactobacillus plantarum strains CIT3 and V7B3 to apples and lettuce, respectively, increased both the safety and shelf-life. Moreover, combining the selected strains with natural antimicrobials produced a further increase in the shelf-life of these products without detrimental effects on the organoleptic qualities.
TL;DR: Evaluation of bread characteristics revealed that the addition of L. amylovorus fermented sourdough improved bread quality and higher safety due to an extended shelf life, and therefore meeting consumer needs for good quality and preservatives-free food products.
Abstract: The present study investigated the antifungal activity of Lactobacillus amylovorus DSM19280 as a starter culture for gluten-free quinoa sourdough bread under pilot-plant conditions to extend the microbial shelf life. Challenge tests against environmental moulds were conducted and a negative control with non-antifungal strain, L. amylovorus DSM20531T, as well as a chemically acidified and a non-acidified control were included. Organic acid production, antifungal metabolites, carbohydrates changes during fermentation and bread quality were compared to wheat counterparts. The application of quinoa sourdough fermented with the antifungal L. amylovorus DSM19280 extended the mould free shelf life by 4 days compared to the non-acidified control. No significant difference in lactic acid production was found between the lactobacilli strains. HPLC-UV/DAD was used to quantify antifungal compounds. The concentration of 4-hydroxyphenyllactic acid, phloretic acid, 3-phenyllactic acid and hydroferulic acid were significantly higher (P
TL;DR: Bio-control of L.monocytogenes with lytic bacteriophage preparations such as ListShield™ can offer an environmentally-friendly, green approach for reducing the risk of listeriosis associated with the consumption of various foods that may be contaminated with L. monocyTogenes.
Abstract: ListShield™, a commercially available bacteriophage cocktail that specifically targets Listeria monocytogenes, was evaluated as a bio-control agent for L. monocytogenes in various Ready-To-Eat foods. ListShield™ treatment of experimentally contaminated lettuce, cheese, smoked salmon, and frozen entrees significantly reduced (p < 0.05) L. monocytogenes contamination by 91% (1.1 log), 82% (0.7 log), 90% (1.0 log), and 99% (2.2 log), respectively. ListShield™ application, alone or combined with an antioxidant/anti-browning solution, resulted in a statistically significant (p < 0.001) 93% (1.1 log) reduction of L. monocytogenes contamination on apple slices after 24 h at 4 °C. Treatment of smoked salmon from a commercial processing facility with ListShield™ eliminated L. monocytogenes (no detectable L. monocytogenes) in both the naturally contaminated and experimentally contaminated salmon fillets. The organoleptic quality of foods was not affected by application of ListShield™, as no differences in the color, taste, or appearance were detectable. Bio-control of L. monocytogenes with lytic bacteriophage preparations such as ListShield™ can offer an environmentally-friendly, green approach for reducing the risk of listeriosis associated with the consumption of various foods that may be contaminated with L. monocytogenes.
TL;DR: The results of this study suggest that the dominant species of sourdough LAB and yeasts dominated also the house microbiota.
Abstract: This study aimed at understanding the extent of contamination by lactic acid bacteria (LAB) and yeasts from the house microbiotas during sourdough back-slopping. Besides sourdoughs, wall, air, storage box, dough mixer and flour of four bakeries were analyzed. Based on plate counts, LAB and yeasts dominated the house microbiota. Based on high throughput sequencing of the 16S rRNA genes, flour harbored the highest number of Firmicutes, but only few of them adapted to storage box, dough mixer and sourdough. Lactobacillus sanfranciscensis showed the highest abundance in dough mixer and sourdoughs. Lactobacillus plantarum persisted only in storage box, dough mixer and sourdough of two bakeries. Weissella cibaria also showed higher adaptability in sourdough than in bakery equipment, suggesting that flour is the main origin of this species. Based on 18S rRNA data, Saccharomyces cerevisiae was the dominant yeast in house and sourdough microbiotas, excepted one bakery dominated by Kazachstania exigua. The results of this study suggest that the dominant species of sourdough LAB and yeasts dominated also the house microbiota.
TL;DR: The results indicate that the microbiological risk posed by Aeromonas should be considered for marine shrimp species that are cultured in low-salinity ponds, and these shrimps may also be a vehicle for the transfer of different genotypes of aeromonas and antibiotic-resistant determinants to regions worldwide through trade.
Abstract: We aimed to document the risk of Aeromonas spp. in marine shrimp species cultured in inland low salinity ponds in Thailand. In 14 of 18 shrimp samples retrieved from inland grow-up ponds, Aeromonas spp. were detected at ranges from 4667 to 1,500,000 CFU/g body weight. The phylogenetic tree constructed with the gyrB and cpn60 concatenated sequences indicated that the 87 isolates consisted of Aeromonas veronii (70%) , Aeromonas aquariorum (18%) , Aeromonas caviae (7%) , Aeromonas jandaei (2%), and Aeromonas schubertii (2%). The potential virulence of the isolates was examined by phenotypic and PCR assays. Hemolytic activity and the extracellular activity of lipase, DNase, and gelatinase were observed in most isolates (94–99%). PCR revealed the presence of 9 genes related to virulence in the 87 isolates: act (75%), aer (74%), alt (30%), ast (1%), ascV (34%), aexT (24%), fla (92%), ela (34%), and lip (24%). The susceptibility profiles to 14 antimicrobial agents of isolates were typical for the genus, but resistance to cefotaxime, a third-generation cephalosporin, and imipenem were found in two A. aquariorum and in three A. veronii isolates, respectively. These resistances were confirmed by determining minimum inhibitory concentrations. Our results indicate that the microbiological risk posed by Aeromonas should be considered for marine shrimp species that are cultured in low-salinity ponds. These shrimps may also be a vehicle for the transfer of different genotypes of Aeromonas and antibiotic-resistant determinants to regions worldwide through trade.
TL;DR: Although coagulase-negative staphylococci are not classical food poisoning bacteria, its presence in food could be of public health significance due to the possible spread of antibiotic resistance.
Abstract: The aim of this work was to study the pheno- and genotypical antimicrobial resistance profile of coagulase negative staphylococci (CoNS) isolated from 146 ready-to-eat food of animal origin (cheeses, cured meats, sausages, smoked fishes). 58 strains were isolated, they were classified as Staphylococcus xylosus (n ¼ 29), Staphylococcus epidermidis (n ¼ 16); Staphylococcus lentus (n ¼ 7); Staphylococcus saprophyticus (n ¼ 4); Staphylococcus hyicus (n ¼ 1) and Staphylococcus simulans (n ¼ 1) by phenotypic and genotypic methods. Isolates were tested for resistance to erythromycin, clindamycin, gentamicin, cefoxitin, norfloxacin, ciprofloxacin, tetracycline, tigecycline, rifampicin, nitrofurantoin, linezolid, trimetoprim, sulphamethoxazole/trimethoprim, chloramphenicol, quinupristin/dalfopristin by the disk diffusion method. PCR was used for the detection of antibiotic resistance genes encoding: methicillin resistance e mecA; macrolide resistance e erm(A), erm(B), erm(C), mrs(A/B); efflux proteins tet(K) and tet(L) and ribosomal protection proteins tet(M). For all the tet(M)-positive isolates the presence of conjugative transposons of the Tn916eTn1545 family was determined. Most of the isolates were resistant to cefoxitin (41.3%) followed by clindamycin (36.2%), tigecycline (24.1%), rifampicin (17.2%) and erythromycin (13.8%). 32.2% staphylococcal isolates were multidrug resistant (MDR). All methicillin resistant staphylococci harboured mecA gene. Isolates, phenotypic resistant to tetracycline, harboured at least one tetracycline resistance determinant on which tet(M) was most frequent. All of the isolates positive for tet(M) genes were positive for the Tn916eTn1545 -like integrase family gene. In the erythromycinresistant isolates, the macrolide resistance genes erm(C) or msr(A/B) were present. Although coagulase-negative staphylococci are not classical food poisoning bacteria, its presence in food could be of public health significance due to the possible spread of antibiotic resistance.
TL;DR: The aims of this study were to isolate LAB with anti-Listeria activity from salami samples, characterize the bacteriocin/s produced by selected isolates, semi-purify them and evaluate their effectiveness for the control of Listeria monocytogenes during manufacturing of salami in a pilot scale.
Abstract: The aims of this study were to isolate LAB with anti-Listeria activity from salami samples, characterize the bacteriocin/s produced by selected isolates, semi-purify them and evaluate their effectiveness for the control of Listeria monocytogenes during manufacturing of salami in a pilot scale. Two isolates (differentiated by RAPD-PCR) presented activity against 22 out of 23 L. monocytogenes strains for bacteriocin MBSa2, while the bacteriocin MBSa3 inhibited all 23 strains in addition to several other Gram-positive bacteria for both antimicrobials and were identified as Lactobacillus curvatus based on 16S rRNA sequencing. A three-step purification procedure indicated that both strains produced the same two active peptides (4457.9 Da and 4360.1 Da), homlogous to sakacins P and X, respectively. Addition of the semi-purified bacteriocins produced by Lb. curvatus MBSa2 to the batter for production of salami, experimentally contaminated with L. monocytogenes (10(4)-10(5) CFU/g), caused 2 log and 1.5 log reductions in the counts of the pathogen in the product after 10 and 20 days respectively, highlighting the interest for application of these bacteriocins to improve safety of salami during its manufacture.
TL;DR: An accelerated fermentation of Bella di Cerignola table olives was achieved using the selected lactobacilli and yeast strains, which markedly affected the amounts of free amino acids, phenolic and volatile organic compounds.
Abstract: This study aimed to utilize an "omics" approach to evaluate the ability of selected lactobacilli and yeasts to improve the fermentation process of Bella di Cerignola table olives. Four types of fermentations were performed at the pilot-plant scale: un-started fermented olives used as a control (Ctrl); olives started with a commercial Lactobacillus plantarum strain (S); commercial L. plantarum strain and autochthonous yeast Wickeramomyces anomalus DiSSPA73 (SY); and L. plantarum, W. anomalus DiSSPA73, autochthonous L. plantarum DiSSPA1A7 and Lactobacillus pentosus DiSSPA7 (SYL). Compared to Ctrl, S, SY, SYL showed a higher acidification (P < 0.05) of the brine, which reached a pH value of 4.49 after one day of fermentation. The microbiota of unfermented olives and brine after one day of fermentation was primarily composed of Enterobacteria that belonged to Hafnia alvei and Methylobacterium. However, L. plantarum and L. pentosus dominated the total and metabolically active microbiota of the Ctrl brines and olives at the end of the fermentation. The use of lactobacilli and W. anomalus DiSSPA73 as a starter culture markedly affected the microbiota of the brines after one day of fermentation. The number of species (OTU) and the results of an alpha diversity analysis indicated that the microbial diversity of the brines was markedly simplified by the S, SY and, in particular, SYL fermentations. According to the lowest biodiversity, S, SY and SYL samples showed the lowest abundance of Proteobacteria, including Enterobacteriacea, Lactococcus lactis, Propionibacterium acidipropionici and Clostridium. The lactobacilli and W. anomalus DiSSPA73 used in this study markedly affected the amounts of free amino acids, phenolic and volatile organic compounds. Both a texture profile analysis and a sensory evaluation showed the highest appreciation for all of the started table olives. As shown through microbiological, biochemical, and sensory analyses, an accelerated fermentation of Bella di Cerignola table olives was achieved using the selected lactobacilli and yeast strains.
TL;DR: DGGE results showed that fungal diversity in daqu was greater than that in AF and AAF, which could help understand dynamics of microbial community succession in continuous fermentation of traditional Chinese vinegars.
Abstract: The traditional fermentation of Shanxi aged vinegar (SAV), a well-known traditional Chinese vinegar, generally involves the preparation of starter daqu, starch saccharification, alcoholic fermentation (AF) and acetic acid fermentation (AAF). Dynamics and diversity of microbial community succession in daqu and other fermentation stages were investigated by denaturing gradient gel electrophoresis (DGGE). Results showed that eight bacterial genera and four fungal genera were found in daqu. However, Staphylococcus, Saccharopolyspora, Bacillus, Oceanobacillus, Enterobacter, Streptomyces, Eurotium, Monascus and Pichia in daqu were eradicated during AF. Four bacterial genera and three fungal genera were found in this stage. Weissella, Lactobacillus, Streptococcus, Saccharomyces, and Saccharomycopsis were the dominant microorganisms in the late stage of AF. During AAF, four bacterial genera and four fungal genera were found. Weissella, Streptococcus, Klebsiella, Escherichia, and Cladosporium gradually disappeared; the dominant microorganisms were Acetobacter, Lactobacillus, Saccharomycopsis, and Alternaria in the late stage of AAF. Alpha diversity metrics showed that fungal diversity in daqu was greater than that in AF and AAF. By contrast, bacterial diversity decreased from daqu to AF and increased in the first three days of AAF and then decreased. Hence, these results could help understand dynamics of microbial community succession in continuous fermentation of traditional Chinese vinegars.
TL;DR: In insights into the ability of co-localized isolates to influence co-culture biofilm production with high relevance for food safety and food production facilities, two specific isolates were found to be present in synergistic combinations with higher frequencies.
Abstract: Bacterial attachment and biofilm formation can lead to poor hygienic conditions in food processing environments. Furthermore, interactions between different bacteria may induce or promote biofilm formation. In this study, we isolated and identified a total of 687 bacterial strains from seven different locations in a meat processing environment and evaluated their biofilm formation capability. A diverse group of bacteria was isolated and most were classified as poor biofilm producers in a Calgary biofilm device assay. Isolates from two sampling sites, the wall and the meat chopper, were further examined for multispecies biofilm formation. Eight strains from each sampling site were chosen and all possible combinations of four member co-cultures were tested for enhanced biofilm formation at 15 °C and 24 °C. In approximately 20% of the multispecies consortia grown at 15 °C, the biofilm formation was enhanced when comparing to monospecies biofilms. Two specific isolates (one from each location) were found to be present in synergistic combinations with higher frequencies than the remaining isolates tested. This data provides insights into the ability of co-localized isolates to influence co-culture biofilm production with high relevance for food safety and food production facilities.
TL;DR: In-depth metagenomic analysis unveiled functionalities involved in bacterial competitiveness, such as the occurrence of CRISPRs and potential bacteriocin production, and the applicability of the selected strains as functional starter cultures.
Abstract: A high-resolution functional metagenomic analysis of a representative single sample of a Brazilian spontaneous cocoa bean fermentation process was carried out to gain insight into its bacterial community functioning. By reconstruction of microbial meta-pathways based on metagenomic data, the current knowledge about the metabolic capabilities of bacterial members involved in the cocoa bean fermentation ecosystem was extended. Functional meta-pathway analysis revealed the distribution of the metabolic pathways between the bacterial members involved. The metabolic capabilities of the lactic acid bacteria present were most associated with the heterolactic fermentation and citrate assimilation pathways. The role of Enterobacteriaceae in the conversion of substrates was shown through the use of the mixed-acid fermentation and methylglyoxal detoxification pathways. Furthermore, several other potential functional roles for Enterobacteriaceae were indicated, such as pectinolysis and citrate assimilation. Concerning acetic acid bacteria, metabolic pathways were partially reconstructed, in particular those related to responses toward stress, explaining their metabolic activities during cocoa bean fermentation processes. Further, the in-depth metagenomic analysis unveiled functionalities involved in bacterial competitiveness, such as the occurrence of CRISPRs and potential bacteriocin production. Finally, comparative analysis of the metagenomic data with bacterial genomes of cocoa bean fermentation isolates revealed the applicability of the selected strains as functional starter cultures.
TL;DR: Results showed that both meat and dairy isolates were more resistant than the ATCC reference strain, and use of sub-lethal stresses in food preservation systems may stimulate antibiotic resistance responses in L. monocytogenes strains.
Abstract: Prevalence of antibiotic resistance of Listeria monocytogenes isolated from a variety of foods has increased in many countries. L. monocytogenes has many physiological adaptations that enable survival under a wide range of environmental stresses. The objective of this study was to evaluate effects of osmotic (2, 4, 6, 12% NaC), pH (6, 5.5, 5.0) and cold (4 °C) stresses on susceptibility of three isolates of L. monocytogenes towards different antibiotics. The minimal inhibitory concentrations (MICs) of tested antibiotics against unstressed (control), stressed or post-stressed L. monocytogenes isolates (an ATCC strain and a meat and dairy isolate) were determined using the broth microdilution method. Unstressed cells of L. monocytogenes were sensitive to all tested antibiotics. In general, when L. monocytogenes cells were exposed to salt, cold and pH stresses, their antibiotic resistance increased as salt concentration increased to 6 or 12%, as pH was reduced to pH 5 or as temperature was decreased to 10 °C. Results showed that both meat and dairy isolates were more resistant than the ATCC reference strain. Use of sub-lethal stresses in food preservation systems may stimulate antibiotic resistance responses in L. monocytogenes strains.
TL;DR: Examination of non-starter lactobacilli isolated from cheeses for their proteolytic activity and capability to produce fermented milk enriched in angiotensin-converting enzyme (ACE)-inhibitory and antioxidant peptides supports Lb.
Abstract: This study aimed at evaluating non-starter lactobacilli (NSLAB) isolated from cheeses for their proteolytic activity and capability to produce fermented milk enriched in angiotensin-converting enzyme (ACE)-inhibitory and antioxidant peptides. Preliminarily, 34 NSLAB from Parmigiano Reggiano (PR) and 5 from Pecorino Siciliano cheeses were screened based on their capacity to hydrolyze milk proteins. Two NSLAB strains from PR, Lactobacillus casei PRA205 and Lactobacillus rhamnosus PRA331, showed the most proteolytic phenotype and were positively selected to inoculate sterile cow milk. The fermentation process was monitored by measuring viable cell population, kinetic of acidification, consumption of lactose, and synthesis of lactic acid. Milk fermented with Lb. casei PRA205 exhibited higher radical scavenging (1184.83 ± 40.28 mmol/L trolox equivalents) and stronger ACE-inhibitory (IC50 = 54.57 μg/mL) activities than milk fermented with Lb. rhamnosus PRA331 (939.22 ± 82.68 mmol/L trolox equivalents; IC50 = 212.38 μg/mL). Similarly, Lb. casei PRA205 showed the highest production of ACE-inhibitory peptides Val-Pro-Pro and Ile-Pro-Pro, which reached concentrations of 32.88 and 7.52 mg/L after 87 and 96 h of milk fermentation, respectively. This evidence supports Lb. casei PRA205, previously demonstrated to possess characteristics compatible with probiotic properties, as a promising functional culture able to promote health benefits in dairy foods.