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Attività antimicrobica di oli essenziali contro ceppi di Bacillus spp. e modifica dell’espressione di geni coinvolti nella risposta allo stress
No full textBacillus spp. comprende specie alteranti e patogene, che possono costituire un pericolo per la qualità e per la sicurezza degli alimenti. Questo lavoro mira a valutare gli effetti del trattamento con oli essenziali (OE) in ceppi di Bacillus spp. isolati da gnocchi ambient, stabili a temperatura ambiente. Tale trattamento rappresenta un evento stressante per la cellula che, a seconda della concentrazione e del tipo di OE applicato, può andare incontro a morte o subire danni, modificando l’espressione di specifici geni.
Sei OE (Thymus vulgaris chemiotipo timolo, Thymus vulgaris chemiotipo p-cimene e timolo, Thymbra capitata chemiotipo carvacrolo, Origanum vulgare chemiotipo carvacrolo, Syzygium aromaticum chemiotipo eugenolo e Ocimum basilicum chemiotipo linalolo) sono stati saggiati contro 25 ceppi di Bacillus spp. (B. subtilis, B. cereus, B. thuringiensis e B. paranthracis) isolati da gnocchi ambient. La ricerca delle Minime Concentrazioni Inibenti (MIC) e Battericide (MBC) (1) e della Concentrazione Inibitoria Frazionaria (FIC) attraverso il metodo Checkerboard sono stati utilizzati per valutarne l’attività in singolo o combinata. L’espressione genica è stata valutata attraverso Real-time RT-PCR quantitativa.
Gli OE di T. vulgaris (timolo), T. capitata e O. vulgare sono risultati i più attivi, con MIC a 48 ore e MBC tra 0.31-1.25 μL/mL (Fig. 1), e hanno mostrato azione commutativa se combinati a OE di S. aromaticum. I ceppi di B. subtilis sono stati leggermente più sensibili rispetto alle altre specie. L’esposizione di ceppi di B. subtilis e B. cereus a concentrazioni subletali di OE di T. vulgaris (timolo), uno tra i più attivi, ha aumentato l’espressione di geni coinvolti nell’integrità di membrana e nel quorum sensing a partire da 6-12 ore di esposizione. I geni maggiormente sovra-espressi sono stati diversi per le due specie (pbpF per B. subtilis e plcR per B. cereus).
In generale, gli OE con chemiotipo timolo e carvacrolo sono risultati i più attivi, anche in combinazione con OE di S. aromaticum ma non con OE di O. basilicum. L’esposizione a OE di timo ha prodotto un evento stressante con aumento della fase lag dei microrganismi, che in questo modo tentano di riparare i danni alla membrana e di restaurare i meccanismi di comunicazione fondamentali per la sopravvivenza.
In conclusione, gli OE di T. vulgaris (timolo), T. capitata e O. vulgare potrebbero essere utili per applicazioni alimentari contro Bacillus spp., anche in combinazione con OE meno attivi
Gene expression dynamics in Bacillus cereus and Bacillus subtilis treated with Thymus vulgaris and Origanum vulgare subsp. hirtum essential oils
No full textEssential oils (EOs) hold significant potential as antimicrobials in food, due to their high concentration of active phenolic compounds. These compounds can target bacterial cells through various mechanisms, such as membrane disruption, quorum sensing inhibition, and interference in virulence factors, affecting microorganisms at a genomic level. Bacillus cereus and Bacillus subtilis are key foodborne bacteria that could be managed using these natural preservatives. The present study investigated the effects of stress induced by applying Thymus vulgaris and Origanum vulgare subsp. hirtum EOs on genetic modifications in B. cereus 11 and B. subtilis 58C strains isolated from shelf-stable gnocchi, through their gene expression analysis by quantitative real-time RT-PCR. Sublethal EO concentrations were tested, at increasing time intervals (6, 12, 18, 24, and 48 h). Most of the genes were downregulated at 6 h, indicating that the stressful situation prolonged the lag phase. Only spo0A for both B. cereus and B. subtilis, and pbpF and sigB for B. subtilis were upregulated after 6 h, suggesting an attempt to restore cellular communication and repair membrane damage. The pbpF gene was the most significant in the stress response of B. subtilis. Conversely, B. cereus responded through different mechanisms, primarily driven by the plcR and nheB genes, illustrating the role of virulence mechanisms in its stress response. In both strains, the genes were generally more upregulated at a higher concentration of EO (0.58 mg/mL), which was more stimulating than at 0.29 mg/mL. Moreover, the two EOs elicited variable stress responses, which implies different cellular mechanisms and genes in the same microorganism. Therefore, the outcomes of this study suggest that the action of the two EOs mainly influenced cell membrane integrity and quorum sensing mechanisms, with differences in the genes involved for the two species and the two EOs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Molecular Characterization of Bacillus spp. Isolated from Ambient Gnocchi and Evaluation of a Biopreservation Approach
No full textBacillus spp. can be a risk for consumers and cause food spoilage. Fifty-four strains of Bacillus spp. were isolated from Italian ambient gnocchi in different storage conditions and formulations. The strains were identified and characterized by Whole Genome Sequencing (WGS), treated with Thymus vulgaris essential oil (TOE) and the effects were evaluated by the expression of some genes involved in stress response.
Method: The genomes of the 54 Bacillus strains, obtained by WGS, were identified and characterized by Ribosomal MLST tool (rMLST) and k-SNP3 analysis. Phylogenetic trees based on the housekeeping genes gyrB, rpoB, and tuf were also realized to confirm species identification. Genes distances were determined from alignments through the Jukes-Cantor method, while the dendrogram was obtained with the Neighbor-
Joining method. After that, virulence factors, antibiotic resistance, and bacteriocin production genes were retrieved by the genomes by the Basic Local Alignment Search Tool (BLAST), to highlight potential negative or positive roles of the isolates in gnocchi. Then, two isolates of the most found species (Bacillus cereus 11 and Bacillus subtilis 58L) were exposed to Thymus vulgaris essential oil (TOE), to evaluate the Minimum
Inhibitory Concentration (MIC). Subsequently, real-time RT-PCR SYBR green was used to investigate the expression of some genes involved in the stress mechanisms induced by sublethal concentrations of TOE at increasing exposure times.
Results: Phylogenetically, close Bacillus spp. strains were isolated from both ambient gnocchi and their ingredients, especially rice flour, starch, and turmeric, showing how the contamination of the raw materials is crucial for the safety and quality of the finished product. The pathogenic species B. cereus, B. thuringiensis, and B. paranthracis were isolated from not-spoiled gnocchi, and this finding represents a risk for consumers. The
presence of virulence and antibiotic resistance genes in the genomes of these isolates confirms their pathogenic potential. In detail, one isolate of B. cereus and one of B. thuringiensis harbored the cescC gene, linked to the production of cereulide, a peptide which constitutes the emetic toxin of B. cereus, responsible for emetic
syndrome and liver failure. Instead, B. subtilis was the most isolated species, also from gnocchi with evident spoilage (slime and reddish discoloration), and this demonstrates its ability to spoil gnocchi and grow even in non-permissive conditions. In fact, isolation from gnocchi with lactic acid in the formulation demonstrates the resistance of B. subtilis strains to low pH. Furthermore, some B. subtilis isolates retrieved genes for the bacteriocin subtilin biosynthesis, revealing potential positive properties. Regarding the antimicrobial effect of TEO, MIC value was 1.25 μL/mL for B. cereus 11 and B. subtilis 58L. At sublethal concentrations (0.31 μL/mL and 0.63 μL/mL) TEO lengthened the lag phase of microorganisms and determined the upregulation of genes involved in mechanisms of response to stress due to exposure to the antimicrobial agent, such as repair
of membrane damage, restoration of quorum sensing mechanisms, biofilm formation, and mobility (pbpF, spoA, plcR, sinR).
Discussion: Our data provide new insights on the spoilage and pathogenic potential of Bacillus spp. in ambient gnocchi, a product whose market penetration is increasing in Italy. In view of the elimination of preservatives, TEO provides a stressful effect, capable of triggering defense mechanisms. Therefore, these results are promising for future applications in food environments
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