186,370 research outputs found
Prevention of sudden cardiac death: focus on the subcutaneous implantable cardioverter-defibrillator
No full textThe implantable cardioverter-defibrillator (ICD) is the most effective therapy to prevent sudden cardiac death (SCD) in high-risk patients. To overcome infections and failure of transvenous leads, the most frightening complications of conventional ICDs, a completely subcutaneous ICD (S-ICD) has been developed and is currently adopted in routine clinical practice. In view of their long life-expectancy, low competitive risk of dying from non-arrhythmic causes, and high lifetime risk of lead-related complications requiring surgical revisions, young patients with cardiomyopathies and inherited arrhythmia syndromes have traditionally been considered ideal candidates for the S-ICD. However, as growing evidence supported S-ICD safety and efficacy, initial niche implant indications were abandoned in favor of a widespread use of this technology, that is currently adopted in common ICD candidates with severe left ventricular dysfunction. Indeed, guidelines recommend S-ICD implantation as an alternative to TV-ICDs in all ICD candidates, unless pacing is required. This review focuses on the contemporary experience with the S-ICD and explores future scenarios in which device-to-device communication will enable to combine leadless therapies
Study of the Interaction Mechanism in the Biosorption of Copper(II) Ions onto Posidonia oceanica and Peat
No full textA systematic approach was used to characterize the biosorption of copper(II) onto two biosorbents, Posidonia oceanica and peat, focusing on the interaction mechanisms, the copper(II) sorption–desorption process and the thermal behavior of the biosorbents. Sorption isotherms at pH 4–6 were obtained and the experimental data were fitted to the Langmuir model with a maximum uptake (qmax) at pH 6 of 85.78 and 49.69mgg_1, for P. oceanica and peat, respectively. A sequential desorption (SD) with water, Ca(NO3)2, and EDTA was applied to copper-saturated biosorbents. Around 65–70% copper(II) were desorbed with EDTA, indicating that this heavy metal was strongly bound. The reversibility of copper(II) sorption was obtained by desorption with HCl and SD. Fourier transform IR spectroscopy (FTIR) analysis detected the presence of peaks associated with OH groups in aromatic and aliphatic structures, CH, CH2, and CH3 in aliphatic structures, COO- and COOH groups and unsaturated aromatic structures on the surface of both biosorbents, as well as peaks corresponding to Si—O groups on the surface of peat. The results of SEM-EDX and FTIR analysis of copper-saturated samples demonstrated that ion exchange was one of the mechanisms involved in copper(II) retention. Thermal analysis of biosorbent samples showed that copper(II) sorption–desorption processes affected the thermal stability of the biosorbents
Mechanisms of clostridium tyrobutyricum removal through natural creaming of milk: a microscopy study
No full textClostridium tyrobutyricum is the main spoilage agent of late blowing defect (LBD) in Grana Padano and Parmigiano-Reggiano cheeses; LBD is characterized by openings and holes and is sometimes accompanied by cracks and an undesirable flavor. Even a very few spores remaining in the cheese curd may cause LBD; thus, it is essential to eradicate them during milk natural creaming. By this process, most of the bacteria, somatic cells, and spores rise to the top of the milk, together with the fat globules, and are removed with the cream. Previous studies suggested that milk immunoglobulins mediate the interactions between fat globules and bacteria that occur upon creaming but no direct evidence for this has been found. Moreover, other physical chemical interactions could be involved; for example, physical entrapment of spores among globule clusters. To maximize the efficiency of the natural creaming step in removing Cl. tyrobutyricum,, it is essential to understand the nature of spore globule interactions. With this aim, raw milk was contaminated with spores of Cl. tyrobutyricum before going to creaming overnight at 8 degrees C, after which spore and bacteria removal was >90%. The obtained cream was analyzed by light interference contrast and fluorescence microscopy and by transmission electron microscopy (TEM). Results showed that most of the vegetative cells and spores, which were stained with malachite green before addition to milk, adhered tightly to the surface of single fat globules, the membranes of which appeared heterogeneous when stained with the fluorescent dye DilC(18)(3)-DS. Using the same dye, we observed transient and persistent interactions among globules, with formation of clusters of different sizes and partial coalescence of adhering membranes. Transmission electron microscopy examination of replicates of freeze-fractured cream allowed us to observe tight adhesion of spores to fat globules. Ultrathin sections revealed that this adhesion is mediated by an amorphous, slightly electron-opaque material, sometimes granular in appearance. Bacteria also adhered to different fat globules, linking them together, which suggests that adhesion was strong enough to maintain a stable contact. Although we cannot exclude physical entrapment of bacteria among fat globule clusters, we show for the first time that most of the bacteria are adhered to fat globules by an electron-opaque material whose nature has yet to be determined. Immunoglobulins are certainly the best candidates for adhesion but other compounds may be involved
DEVELOPMENT OF INNOVATIVE TECHNIQUES FOR STUDYING MICROBIAL POPULATIONSIN MILK AND DAIRY PRODUCTS
No full textABSTRACT
Within the complex bacterial community of traditional raw milk cheeses, lactic acid bacteria (LAB), naturally present in the milk as adventitious contaminants, play the key role in the cheese manufacture and ripening process through their acidifying, proteolytic and flavouring activities. Moreover, LAB contribute considerably to the microbial safety, since they produce organic acids and bacteriocins that extend shelf-lives of raw milk products. Numerous LAB genera and species such as Lactobacillus, Lactococcus, Streptococcus, Leuconostoc and Enterococcus are involved in these metabolic activities. This natural microbial biodiversity can be considered a heritage which has to be protected and preserved, since alterations in the composition of the beneficial autochthonous microbiota is of critical importance in maintaining the peculiar features of the traditional raw milk products. On the contrary, LAB may have also negative traits, such as the ability to produce toxic biogenic amines, possession of transmittable antibiotic resistance genes, and the potential for expression of putative virulence factors. Dairy safety aspects should include careful examination of these harmful features. Therefore, the study of micro-organisms at species and strain level and the monitor of their dynamics in the microbial community throughout cheese manufacture and ripening is helpful to improve the quality and safety of the final product. Classical microbiological and molecular techniques have been widely used to investigate the dairy biodiversity and to achieve the characterization of bacterial species present in a complex microbial dairy ecosystem, highlighting the advantages and the limitations of both methods.
The aims of PhD thesis were: I) to apply a polyphasic approach based on different phenotypic and molecular techniques for the characterization of the LAB isolated from dairy products collected throughout the technological process of an artisanal raw milk cheese, such as “Formagèla Valseriana”; II) to evaluate the application of total microbial DNA extracted directly from dairy products as template in PCR 16S-23S rRNA region spacer analysis (RSA-PCR) in order to achieve a rapid knowledge about their microbial communities, bypassing the previous step of isolation in pure culture; III) to investigate the influence of equipment (thermocycler) and reagents (Taq polymerase) on results obtained from RSA analysis; IV) to explore the functional and safety aspects of E. faecalis strains isolated from dairy products collected in different North Italy regions through the study of their biodiversity, bacteriocin, volatic organic compounds and biogenic amines production, virulence factors and antibiotic resistance.
Firstly, evolution of bacterial groups during the cheese-making process of “Formagèla Valseriana” was revealed by viable counting of LAB and non-LAB micro-organisms. A total of 143 presumptive LAB strains from milk culture, curd and cheese samples were randomly selected from agar plates and subjected to morphological and phenotypic characterization (microscopic examination, Gram staining, catalase test, growth at 15 and 45 °C, CO2 production from glucose) and molecular identification. To investigate LAB biodiversity, the taxonomic position of the isolates was established through RSA-PCR combined with a species-specific PCR assay. Strains characterized by atypical classes of spacer were identified by partial 16S rRNA sequencing. Random amplified polymorphic DNA analysis (RAPD-PCR) was carried out to explore the genetic diversity of LAB isolates. In addition, this study was intended to evaluate the application of microbial DNA extracted directly from dairy products as template in RSA-PCR in order to achieve a rapid knowledge about their microbial communities, bypassing the previous step of isolation in pure culture. As expected in raw milk cheeses, LAB (i.e. lactobacilli, lactococci and enterococci) were quantitatively the dominant group for all samples. The combination of various molecular procedures allowed many species to be detected. In particular, milk culture showed a prevalence of Streptococcus thermophilus, whereas the most detected LAB in curd belonged to the species Lactococcus lactis ss lactis, Lc. garvieae and Enterococcus durans. E. durans was the species most frequently isolated from cheese samples, even if several species (E. faecalis, E. gilvus, E. italicus, Lb. paracasei ss paracasei, St. bovis, Lb. plantarum, Lb. coryniformis and Ln. mesenteroides), which are indicative of biological richness, were also present. RAPD-PCR revealed a high biodiversity at species level, but it also showed the presence of significant genetic variability among the isolates belonging to the same species. RSA, using as template DNA extracted directly from milk culture, did not prove to be a suitable method for discrimination of microbial species in a complex matrix, since when microbial community was very heterogeneous and rich, it was difficult discerning LAB species or genera. Actually, the band of S. thermophilus represents the only one that could be frequently identified. The 143 LAB strains were then screened for their inhibitory activity against Listeria monocytogenes and Staphylococcus aureus and for their acidifying activity. Seven and six strains, mainly belonging to the Enterococcus genus, exhibited antagonistic activity against L. monocytogenes and S. aureus, respectively. With regard to acidifying activity, the majority of isolates (88.8%) were found to be low acidifying isolates, causing a pH decrease lower than 1.5 pH units, whereas only 16 strains were classified as medium acidifying isolates and could be considered the fastest acidifying strains. Yet, after 24 h 74.1% of the isolates showed a medium acidifying ability and 9.1% were classified as high acidifying strains.
As revealed by screening the microbial population of “Formagèla Valseriana”, the Enterococcus genus is one of the most prevalent within dairy microbial community. However, enterococci are ascribed the most controversial nature, presenting both beneficial and negative features. They represent important nosocomial pathogens, but are also recognized to produce bacteriocin with antibacterial activity and to enhance flavour and aroma development in cheese. For this reason, 40 Enterococcus faecalis strains isolated from raw milk products (milk, curd and cheese) collected throughout the technological process of various North-west Italian traditional cheeses (Aosta Valley, Piedmont and Lombardy) over a 13 year period (1997-2009) were examined.
The genetic biodiversity of E. faecalis isolates was assessed through RAPD-PCR and repetitive extragenic palindromic PCR (rep-PCR). Phenotypic and molecular protocols were applied in order to investigate the incidence of antibiotic resistance and virulence factors among strains. They were examined for their antimicrobial activity against 18 foodborne spoilage and pathogenic bacteria. Investigation was also made to identify their bacteriocinogenic potential by searching for bacteriocin-encoding genes (enterocin A, enterocin B, bacteriocin 31, enterocin P, enterocin Q, enterocin L50A-B, mundticin KS, enterocin CRL35, enterocin AS-48, and enterocin 1071A-B). In addition, they were inoculated in milk and submitted to head-space solid-phase-micro- extraction gas chromatography-mass spectrometry analysis in order to study their capability for production of volatile organic compounds (VOCs).
Resistance to streptomycin (50%), quinupristin-dalfopristin (32.5%), tetracycline (25%), rifampicin (7.5%), chloramphenicol (5%) and erythromycin (2.5%) were evidenced. Ampicillin, ciprofloxacin, levofloxacin, mupirocin, nitrofurantoin, penicillin G and vancomycin were revealed effective antimicrobials against all the strains considered. Tetracycline resistance was also confirmed by detection of tet(M), tet(K), tet(L), tet(S) and transmissibility of resistance by integrase gene (int) of the Tn916/Tn1545 family of transposons. The high incidence of tet(M) gene, found in 90% of the isolates, doesn’t correlate with their phenotypic expression, thus highlighting the presence of silent genes. The phenotypic assay of haemolytic activity showed positive results (β-haemolysis) only in 2 strains. Among the 7 virulence determinants tested, only gel, asa1, esp and efaA genes were harboured. None other gene encoding for either different virulence factors (cylA, hyl, ace), or amino-acid decarbolylase activity (hdc, tdc, odc) was detected. Our results suggest that dairy enterococci don’t represent the major potential reservoir for the spread of the investigated detrimental traits in contrast to other strains of different origin. Considering their antimicrobial activity, all the E. faecalis tested were active against at least 1 of the 18 indicator strains. Remarkable inhibitory effects against harmful or detrimental microbial species, including Bacillus cereus (44.7% of strains), Escherichia coli (17.5%), L. monocytogenes (15%), St. aureus (2.6%), and Clostridium sporogenes (21.1%), was detected. Moderate antagonism towards LAB (65.8% of strains), especially Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus helveticus, was found, too. However, 31.6% of E. faecalis strains were reported as ideal preservatives. Of the 10 enterocin structural genes explored, only gene for enterocin AS-48 was identified, suggesting that the antimicrobial activity of the phenotypically positive isolates should necessarily be due to another enterogenic or non-enterogenic compound. A significant genetic variability was pointed out, but it was no possible to link the enterocin phenotypes and genotypes with the strain origin. No relation with the geographical origin or the period in which the strains were isolated was also found with regard to the VOCs production and very different enzymatic activities among strains was detected. The major volatile compounds produced were: ethanol, diacetyl, acetoin, acetic and benzoic acids. The results of the present study suggested that a polyphasic approach, combining different phenotypical and genotypical methods, may represent an essential tool to obtain a more effective, accurate and exhaustive investigation of the microbial typing.
Finally, even if RSA-PCR was proven to be a rapid, reliable and cost-effective alternative to other PCR methods for the microbial identification and typing, the possibility to compare RSA-PCR results obtained with different thermal cyclers and Taq DNA polymerases has not been investigated effectively. Four models of thermal cyclers of 3 different commercial brands and 4 brands of Taq DNA polymerase were evaluated for their effects on the reproducibility of the RSA-PCR. Five reference LAB strains (St. thermophilus, Lb. helveticus, Lb. delbrueckii subsp. lactis, Lb. delbrueckii subsp. bulgaricus and Lb. fermentum) and a DNA mixture, obtained combining together the DNAs extracted from each reference strain in the same ratio, were used in the experiment. A wide variety of RSA-PCR profiles in terms of band number and size were observed in relation to thermal cycler and Taq DNA polymerase tested, highlighting the relevant influence of these two variables on RSA-PCR reproducibility. It is therefore recommended to choose, within each laboratory, appropriate operating procedures in accordance with one’s equipment and reagents
Study of sorption processes and FT-IR analysis of arsenate sorbed onto red muds (a bauxite ore processing waste)
No full textIn this study we evaluated the arsenate adsorption capacity of red muds (RM), wastes tailing from the alumina production, at different pH values (4, 7, and 10). RM samples were artificially enriched in batch tests with solutions containing increasing concentrations of As(V). The pH of the solution significantly affected the adsorption, which increased with the decrease of pH. Moreover a sequential extraction procedure [H2O; (NH4)2SO4; NH4H2PO4; NH4+-oxalate; NH4+-oxalate + ascorbic acid] was applied to RM samples exchanged with arsenate. Using this approach it was shown that low concentrations of arsenate sorbed in RM were present as water soluble and exchangeable fractions, while NH4+-oxalate and NH4+-oxalate + ascorbic acid extracted most of the adsorbed arsenate from RM at different pH values. Besides, FT-IR spectroscopy was used to better understand the nature of RM surface configuration after As(V) sorption. In the FT-IR spectra the presence of As(V) species was highlighted by a well resolved band at 865 cm−1. The intensity and broadness of this band increased at the decreasing of pH. This band could be related to ν(As–O) vibration of an inner-sphere Al–O–As complex and/or due to As–O bonds of the adsorbed As(V) species on Fe oxides of RM samples
Studio dei processi di adsorbimento tra fanghi rossi (residui derivanti dalla lavorazione della bauxite) e As(V)
No full textIn questo studio è stata esaminata la capacità di fanghi rossi (red muds: RM), residui a tessitura fine derivanti dalla digestione della bauxite, ad adsorbire arseniato. Campioni di RM a tre diversi valori di pH (pH 4, 7, e 10) sono stati contaminati con soluzioni contenenti crescenti concentrazioni di As(V). I risultati dell’indagine indicano che il pH della soluzione influenza l’adsorbimento, che aumenta al diminuire del pH secondo il seguente ordine: RM-As(V) pH 4 (1,91 mmol•g-1)>RM-As(V) pH 7 (0,17 mmol•g-1)>RM-As(V) pH 10 (0,12 mmol•g-1). La dipendenza dell’adsorbimento dal pH può essere spiegata considerando che il punto di carica zero dei RM testati è 4,77. Di conseguenza a pH 4 l’adsorbimento dell’As(V) è regolato soprattutto da interazioni di tipo elettrostatico, mentre a pH 7 e 10 dovrebbe essere attribuibile principalmente ad un adsorbimento specifico.
Al fine di acquisire informazioni sull’attività delle diverse componenti dei RM sui fenomeni di adsorbimento dell’arseniato, campioni di RM saturati con As(V) a pH 4, 7 e 10 sono stati sottoposti a estrazione sequenziale con H2O, (NH4)2SO4, NH4H2PO4, NH4+-ossalato, e NH4+-ossalato+acido ascorbico, e ad analisi FT–IR.
I risultati hanno evidenziato che le frazioni solubili e scambiabili dell’As(V) adsorbito erano minori del 28%, mentre quantità maggiori del 36% sono state estratte con NH4+-ossalato e NH4+-ossalato+acido ascorbico Questi dati suggeriscono che il principale meccanismo che regola l’adsorbimento è ascrivibile ad un chemioadsorbimento, e questo è stato osservato in particolare nei RM saturati con As(V) a pH 10.
Attraverso gli spettri FT–IR di RM-As(V), la presenza dell’arseniato è stata evidenziata da una banda a ̴ 861-865 cm−1, la cui intensità e larghezza aumentava al diminuire del pH. Questa banda potrebbe essere ascritta sia a vibrazioni v(As–O) di complessi a sfera interna Al–O–As, che a legami As–O delle specie di As(V) adsorbite sugli ossidi di Fe dei RM. Pertanto anche la spettroscopia FT–IR ha evidenziato che la maggior parte dell’As(V) era specificatamente associato con gli ossidi e ossi-idrossidi di Fe e Al dei fanghi rossi
Influence of pea and wheat growth on Pb, Cd, and Zn mobility and soil biological status in a polluted amended soil
No full textIn this paper we evaluated the effects of various amendments, notably zeolite, red mud (a by-product of
aluminium manufacturing) and lime on decreasing the bioavailability and phytotoxicity of Pb, Cd and Zn
present in a contaminated acidic soil (pH=4.2). Pisum sativum and Triticum vulgare were grown in a
glasshouse experiment on untreated-polluted (control) and amended soils and their yield and metal uptake
determined. The influence of plants on the total concentration and mobility of Pb, Cd, and Zn, and on several
soil microbiological and biochemical parameters was also evaluated and compared to unplanted (control and
amended) soils on which we have previously reported.
All the amendments enhanced plant yields significantly. Red mud and lime decreased Zn, Pb and Cd
availability to plants, whilst zeolite was efficient only at blocking Pb. Red mud in particular decreased heavy
metal uptake of pea and wheat by 60–34% (Pb), 79–80% (Cd), and 93–64% (Zn) respectively when compared
to the control plants.
After plant growth, Cd and Zn solubility in theamended soilswas significantly higher than in respective unplanted
soils. Likewise, the number of fast-growing heterotrophic bacteria and fungi was higher after pea and wheat
compared to bare soil, and thiswas irrespective of the treatment applied. These data togetherwith Biolog-derived
parameters (AWCD and richness) and enzyme activities (dehydrogenase, urease and â-glucosidase) also
suggested that pea rhizodeposits, in the different soils, were either more abundant or more readily-available to
soil bacterial communities compared to wheat rhizodeposits
XRD, FTIR, and thermal analysis of bauxite ore-processing waste (Red Mud) exchanged with heavy metals
No full textThe present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RMnt) and acid-treated red mud (RMa), a bauxite ore-processing waste, exchanged with Pb2+, Cd2+, and Zn2+ cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii.
The XRD pattern of RMnt, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RMnt: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RMnt exchanged with Pb2+ and Cd2+ cations revealed two additional phases, namely hydrocerussite [Pb3 (CO3)2 (OH) 2 (10 wt.%)] and octavite [CdCO3 (8 wt.%)].
These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples.
In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ~1100 cm–1, which is attributed to the asymmetric stretch of Si–O–Al. This effect may be associated with the Pb2+, Cd2+, and Zn2+ adsorbed by the red muds which caused a deformation of the initial structure.
Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn2+>Cd2+>Pb2+
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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