Genetic relationships and biofilm formation of Listeria monocytogenes isolated from the smoked salmon industry

Among pathogens, L. monocytogenes has the capability to persist on Food Processing Environment (FPE), first of all posing safety issues, then economic impact on productivity. The aim of this work was to determine the influence of biofilm forming-ability and molecular features on the persistence of 19 Listeria monocytogenes isolates obtained from FPE, raw and processed products of a cold-smoked salmon processing plant. To verify the phenotypic and genomic correlations among the isolates, different analyses were employed: serotyping, Clonal Complex (CC), core genome Multi-Locus Sequence Typing (cgMLST) and Single Nucleotide Polymorphisms (SNPs) clustering, and evaluation of the presence of virulence- and persistence-associated genes. From our results, the biofilm formation was significantly higher (*P < 0.05) at 37 °C, compared to 30 and 12 °C, suggesting a temperature-dependent behaviour. Moreover, the biofilm-forming ability showed a strain-specific trend, not correlated with CC or with strains persistence. Instead, the presence of internalin (inL), Stress Survival Islet (SSI) and resistance to erythromycin (ermC) genes was correlated with the ability to produce biofilms. Our data demonstrate that the genetic profile influences the adhesion capacity and persistence of L. monocytogenes in food processing plants and could be the result of environmental adaptation in response to the external selective pressure.

Colletotrichum Gloesporioides Inhibition In Situ by Chitosan-Ruta graveolens Essential Oil Coatings: Effect on Microbiological, Physicochemical, and Organoleptic Properties of Guava (Psidium guajava L.) during Room Temperature Storage

Guava is a fruit appreciated worldwide for its high content of bioactive compounds. However, it is considered a highly perishable fruit, generally attacked by pathogenic species such as the fungi Colletotrichum gloeosporioides, which causes anthracnosis. To diminish the losses caused by pathogenic fungi, coatings of chitosan (CS) with Ruta graveolens essential oil (RGEO) in different concentrations (0.5, 1.0, 1.5% v/v) were applied in situ and their effects on the physical properties and microbiological quality of the guavas were studied. The CS+RGEO coated fruits exhibited better physicochemical behavior and lower microbiological decay as compared to the uncoated guavas, demonstrating the effectiveness of the coatings, especially those with 1.5% of RGEO content. All the fruits coated had greater acceptance and quality than the controls, being more those with essential oil incorporation. In situ investigation of C. gloesporioides infection of guavas demonstrated that the CS+RGEO coated guavas showed a high percentage of inhibition in the development of anthracnose lesions. In the present investigation, an alternative method has been proposed to extend the stability of the guavas fruit up to 12 days with application in the food industry.

Effect of nisin on biogenic amines and shelf life of vacuum packaged rainbow trout (Oncorhynchus mykiss) fillets

Nisin is a lantibiotic exhibiting antimicrobial activity against a wide range of Gram-positive bacteria, or some Gram-negative bacteria when used in combination with other preservative agents. The objective of the present work was to study the effect of nisin treatment on biogenic amines occurrence and shelf life of refrigerated (4 °C) vacuum packaged rainbow trout samples. For this purpose samples were divided in two batches: the experimental batch (CB-N), consisting of samples immersed in sterilized broth formulated with soy milk 1.4% (v/v) and whey powder 11.2% (w/v) dissolved in deionized water with addition of nisin (500 mg L-1); the control batch (CB), consisting of samples immersed in the former broth without addition of nisin. A positive effect of nisin resulted on colour stability; in fact, the global colour index ΔE remained constant during the storage of treated rainbow trout samples, while it increased in the control. However, the behaviour of microbiota, texture, odour and biogenic amines were comparable between fillet samples treated with nisin broth and with control medium (without nisin). No inhibitory effects of nisin on biogenic amines accumulation was observed; conversely, the decline of histamine content (about 30%), observed only in fishes of the control batch, may be correlated to the presence of histamine-degradating bacteria (Pseudomonas species). Further studies are necessary to investigate nisin action mechanism on the colour, an important physical characteristic involved in the product quality and consumer acceptability.

Thymus Vulgaris (Red Thyme) and Caryophyllus Aromaticus (Clove) Essential Oils to Control Spoilage Microorganisms in Pork Under Modified Atmosphere

In recent years, it has been confirmed that essential oils (EOs) exert antimicrobial activity as they are able to inhibit cell growth and inactivate microbial cells. The application of biopreservation strategies by means of EOs opens up interesting perspectives in the food industry, including meat production. The paper aims to evaluate the effects of Thymus vulgaris (red thyme) and Caryophyllus aromaticus (cloves) EOs on the development of the spoilage population of fresh pork packaged under modified atmosphere (MAP). In particular, the research was focused on Brochothrix thermosphacta, a specific spoilage microorganism of fresh meat packed in anaerobic conditions or under MAP. Amongst seven EOs, those that showed the highest antimicrobial activity on 5 B. thermosphacta strains in vitro were: cloves [minimum inhibitory concentration (MIC) 0.6-2.5 mg/mL], savory (MIC 2.5-5.0 mg/mL), and red thyme (MIC 2.5 to 20 mg/mL). Red thyme and cloves EOs were selected for meat treatment, by increasing the dose at 20 and 40 mg/mL respectively, to take into account the matrix effect that can reduce EO availability. In spite of the minor efficacy observed in vitro, 40 mg/mL red thyme EO strongly limited the growth of B. thermosphacta in pork samples up to day 6 of storage [below 3.0 Log colony forming unit (CFU)/g, starting from 2.0 Log CFU/g at time 0], and exerted an antimicrobial effect also on the aerobic mesophilic count. Good results were obtained also with 20 mg/mL red thyme EO. The control of B. thermosphacta growth through EOs encourages research on alternative methods for extending the shelf life of fresh meat under MAP.

Use of Saccharomyces cerevisiae strains endowed with β-glucosidase activity for the production of Sangiovese wine

The aim of this work was to evaluate the suitability of four strains of Saccharomyces cerevisiae endowed with in vitro β-glucosidase activity to improve the Sangiovese wine aroma profiles. In particular the effects of the strains on fermentation kinetics, wine sugar and acid concentrations, volatile molecule profiles and colour parameters were evaluated. Moreover their effects on anthocyanins, anthocyanidins and poliphenols were evaluated. These four strains of S. cerevisiae were tested in comparison with one commercial strain and with a spontaneous fermentation in the presence and in the absence of paraffin oil. The results showed that the four wild strains had high fermentation rates and an efficient conversion of grape sugars to alcohol. However, each strain imparted specific features to the wine. AS11 and AS15 gave rise to wine having low volatile acidity values associated to high levels of linalool and nerolidol. They provoked decrease of anthocyanins accompanied by the increase of some anthocyanidins. S. cerevisiae BV12 and BV14 showed the best performances producing wines with the lowest residual sugar contents and volatile acidity values, high levels of nerolidol and citronellol without detrimental effects on wine colour.

A taxonomic survey of lactic acid bacteria isolated from wheat (Triticum durum) kernels and non-conventional flours

In order to explore the correspondence between raw material- and mature sourdough-lactic acid bacterial (LAB) communities, 59 Italian wheat (Triticum durum) grain samples, one bran and six non-conventional flour samples were analyzed through a culture-dependent approach. The highest cell count by an agar medium specific for LAB was 2.16 log CFU/g. From about 2300 presumptive LAB (Gram-positive and catalase-negative) colonies collected, a total of 356 isolates were subjected to identification by a genetic polyphasic strategy consisting of RAPD-PCR analysis, partial 16S rRNA gene sequencing, species-specific and multiplex PCRs. The isolates were recognized as 137 strains belonging to Aerococcus, Enterococcus, Lactobacillus, Lactococcus and Pediococcus genera and a phylogram based on partial 16S rRNA genes was constructed. The species most frequently found were Enterococcus faecium, Enterococcus mundtii and Lactobacillus graminis, which are not generally reported to be typical in mature sourdoughs.

Histochemical localization of reverse transcriptase in polytene chromosomes of chironomids

The localization of a reverse transcriptase-related protein in salivary gland polytene chromosomes was investigated by immunohistochemistry in two species of Chironomus. The antibodies used were raised against a recombinant protein containing phylogenetically conserved motifs of reverse transcriptases and derived from an abundant non-LTR element previously identified in Chironomus. Immunoreactive protein was found in some telomeres, in a centromeric region, in a few interstitial bands and in Balbiani ring 3. The telomeric signal was probably dependent on transcription and increased dramatically when telomeric heat shock puffs were induced. A correlation with transcription was also seen in Balbiani ring 3, the immunobinding of which disappeared after inhibition of transcription with actinomycin D.

Interspersed DNA element restricted to a specific group of telomeres in the dipteran Chironomus pallidivittatus

Telomeres in the dipteran Chironomus pallidivittatus terminate with 340bp tandem DNA repeats belonging to different subfamilies with characteristic intertelomeric distribution. We have now found, interspersed between such repeats, a composite element of approx. 1400bp present in two similar size variants, with several components of nontelomeric origin. There were about 50 copies of the element, predominantly or exclusively present in a previously defined group of telomeres, characterized by a unique set of telomeric tandem repeat subfamilies. Elements were integrated at irregular distances from each other, and intervening telomeric tandem repeat DNA was variable in composition. Nevertheless, the flanks immediately surrounding the elements were identical for different elements; in other words, there was a site-specific insertion. We suggest that this selective invasion of a small part of the genome by an interspersed, probably rapidly evolving element is best explained by repeated gene conversions.

Interspersed centromeric element with a CENP-B box-like motif in Chironomus pallidivittatus

Short mobile elements are present in different recombined forms as interspersed GC-rich islands between AT rich centromeric 155 bp tandem repeats in the dipteran Chironomus pallidivittatus . The basic element is 80 bp long, has a pronounced invert repeat structure and contains a 17 bp segment similar to the CENP-B box in mammals. The element inserts into a specific site of the 155 bp repeat in a defined orientation surrounded by 2 bp direct repeats. The total number per genome of the main variant is <20. Elements can be present in all centromeres from C.pallidivittatus and the sibling species Chironomus tentans with pronounced differences in distribution within and between species.

Telomeres terminating with long complex tandem repeats

Telomeres of most investigated species terminate with short repeats and are elongated by telomerase. Short repeats have never been detected in dipteran species which have found other solutions to end a chromosome. Whereas in Drosophila melanogaster retroelements are added onto the termini, chironomids have long complex repeats at their chromosome ends. We review evidence that these units are terminal and probably have evolved from short telomeric repeats. In Chironomus pallidivittatus the units have been shown to belong to different subfamilies which have specific inter- and intrachromosomal distribution, the most terminal subfamily of repeats being characterized by pronounced secondary structures for the single strand. The complex repeats are efficiently homogenized both within and between different chromosome ends. Gene conversion is probably an important component in the coordinate evolution of the repeats but it is not known whether it is used for net synthesis of DNA. RNA is used as an intermediate in telomere elongation both by organisms having chromosomes terminating with short repeats and by D. melanogaster. It is therefore interesting that the terminal repeats in chironomids are transcribed.

A family of complex tandem DNA repeats in the telomeres of Chironomus pallidivittatus

A family of 340-bp tandem telomere-associated DNA repeats is present in 50- to 200-kb blocks in seven of the eight paired chromosome ends in Chironomus pallidivittatus. It consists of four main subfamilies, differing from each other by small clusters of mutations. This differentiation may reflect different functional roles for the repeats. Here we find that one subfamily, D3, is consistently localized most peripherally and extends close to the ends of the chromosomes, as shown by its sensitivity to the exonuclease Bal 31. The amounts of D3 are highly variable between individuals. The repeat characteristic for D3 forms a segment with pronounced dyad symmetry, which in single-strand form would give rise to a hairpin. Evidence from an interspecies comparison suggests that a similar structure is the result of selective forces. Another subfamily, M1, is present more proximally in a subgroup of telomeres characterized by a special kind of repeat variability. Thus, a complex block with three kinds of subfamilies may occupy different M1 telomeres depending on the stock of animals. We conclude that subfamilies are differentially distributed between and within telomeres and are likely to serve different functions.