Aquaculture is the fastest-growing sector in food industry. Its development is powered by the intensification of the production which increased bacterial disease occurrence and spreading. As aquaculture deeply relies on a massive prophylactic and therapeutic use of antibiotics, it is threatened by the emergence of multi drug resistant bacteria. The stalled development of new antibiotics makes finding new therapeutic solutions a burning issue. Thanks to their specific host range, their ability to treat both the farmed species and the environment, their limited ecological impact and their abundance in the environment, bacteriophages represent a promising sustainable solution to control pathogenic aquaculture bacteria. In this review we discuss the interest of phage biocontrol for aquaculture and how can bacterial resistance, ecological, pharmacological and production related issues be solved.
-Pulsed electric field (PEF) is an emerging non-thermal processing technology used to inactivate microorganisms in liquid foods such as milk. The objective of this research was to study the effectiveness of continuous PEF equipment (square wave pulses) on total microorganisms of raw skim milk and on Salmonella enteritidis inactivation under moderate temperatures (T < 50 °C). Processing parameters (electric field and pulse width) were chosen as follows: 45 kV·cm -1 /500 ns and 55 kV·cm -1 /250 ns, with increasing pulse frequencies from 40 to 120 Hz, that corresponds to an energy input varying from range 0-100 kJ·kg -1 . In these conditions, the effectiveness of PEF processing on microbial inactivation was very limited: 1.4-log reduction of total microflora and S. enteritidis was the maximal inactivation ratio obtained. The effect of these PEF treatments on physicochemical and technological properties of the milk was also evaluated. These process conditions had an effect on proteinic components of milk such as casein micelles, since viscosity of PEF-treated milk decreased and coagulation properties were enhanced for high field levels (45-55 kV·cm -1 ) with 2.1 to 3.5 µs cumulated treatment time and square waves. This study demonstrated that, contrary to numerous previous studies, PEF treatments had an impact on some food constituents. Résumé -Traitement de lait écrémé cru par champs électriques pulsés à température non létale : efficacité au plan de la destruction microbienne et effet sur les propriétés fonctionnelles. La tendance actuelle de l'industrie alimentaire est de proposer des alternatives aux traitements thermiques de pasteurisation. Ces traitements alternatifs doivent être efficaces sur le plan de la destruction bactérienne, mais moins sévères au plan physico-chimique, afin de garantir la qualité hygiénique des aliments tout en préservant leurs qualités nutritionnelles, sensorielles et fonctionnelles. Les traitements par champs électriques pulsés (CEP) sont souvent reconnus dans la littérature comme un des procédés innovants capables de répondre à ces nouvelles exigences. L'objectif de cette étude était donc ici d'évaluer l'efficacité de traitements en continu par CEP (impulsions élec-triques rectangulaires) réalisés à température non létale (T < 50 °C) sur la destruction de la flore endogène et des coliformes du lait ainsi que sur du lait préalablement inoculé avec Salmonella enteritidis. Les paramètres de traitements choisis (champs électriques et largeur des impulsions) étaient les suivants : 55 kV·cm -1 /250 ns et 45 kV·cm -1 /500 ns, avec des fréquences d'impulsion variant de 40 à 120 Hz, ce qui se traduit par un apport d'énergie compris entre 0 et 100 kJ·kg -1 . Dans ces conditions, l'efficacité des traitements est très limitée puisque au maximum 1,4 log de réduction microbienne a pu être atteint sur la flore endogène et S. enteritidis. Parallèlement, l'effet des traitements par champs électriques pulsés sur les principales caractéristiques physico-chimiques et techno-fonctionnelles du la...
-The conventional plate-counting technique, while still routinely used in laboratories requiring micro-organism screening or enumeration, remains time-consuming and tiresome for the operator when large numbers of samples are assayed. We developed a miniaturized method based on serial tenfold dilution of samples in 96-well micro-plates followed by multiple pour-plating into 24-well micro-plates with an agar overlay procedure, providing easy colony counting and interpretation. The accuracy, sensitivity and reproducibility of this miniaturized method were tested using the conventional plate-counting technique as reference for viability measurements of Escherichia coli cells submitted to a sub-lethal thermic stress, enumeration of lactic bacteria during milk fermentation, and analysis of the total aerobic flora, coliform and Staphylococcus aureus content of spoiled food. No significant differences were found between the results obtained with our miniaturized method and the conventional one, regardless of the bacteria and media used. Providing a reduction in overall cost and handling time, this reliable miniaturized method should be useful for experiments involving large ranges of cell concentration as well as great numbers of samples and replicates. Résumé -Développement d'une méthode de dénombrement microbien rapide et peu coûteuse basée sur la miniaturisation de la méthode classique de dénombrement après culture sur gélose. La méthode classique de dénombrement des micro-organismes après culture en milieu gélosé est toujours très utilisée dans les laboratoires de microbiologie. Elle est cependant coûteuse en temps et devient fastidieuse pour des études mettant en jeu un grand nombre d'échantillons et/ou nécessitant de nombreuses répétitions. Nous avons développé une méthode miniaturisée basée sur le même principe que la méthode classique mais utilisant des plaques 96 puits pour la phase de dilution décimale des échantillons et des plaques 24 puits pour la phase d'ensemencement des dilutions dans l'agar, ceci permettant le traitement d'un grand nombre d'échantillons en gardant la même facilité de comptage et d'interprétation des colonies. La fiabilité, la sensibilité et la reproductibilité de cette méthode miniaturisée ont été vérifiées en utilisant la technique conventionnelle comme référence pour des dénombrements de cellules d'Escherichia coli soumises à un traitement thermique subléthal, de bactéries lactiques au cours de la fermentation du lait en yaourt et de la flore méso-phile, des coliformes totaux et de Staphylococcus aureus dans des aliments. Aucune différence significative n'a été mise en évidence entre les résultats obtenus par les deux méthodes, quels que soient les bactéries et le milieu de culture. Cette microméthode de dénombrement après culture en milieu gélosé permet donc des réductions de coût et de temps de manipulation avec la même fiabilité que la méthode classique. Elle peut donc être utile pour toutes les expériences impliquant une gamme étendue de concentrations bactériennes ainsi ...
Bacillus cereus group is widespread in nature and foods. Several members of this group are recognized as causing food spoilage and/or health issues. This study was designed to determine the prevalence and genetic diversity of the B. cereus group strains isolated in Tunisia from different foods (cereals, spices, cooked food, fresh-cut vegetables, raw and cooked poultry meats, seafood, canned, pastry, and dairy products). In total, 687 different samples were collected and searched for the presence of the B. cereus group after selective plating on MYP agar and enumeration of each sample. The typical pink-orange uniform colonies surrounded by a zone of precipitate were assumed to belong to the B. cereus group. One typical colony from each sample was subcultured and preserved as cryoculture. Overall, 191 (27.8%) food samples were found positive, giving rise to a collection of 191 B. cereus-like isolates. The concentration of B. cereus-like bacteria were below 103 cfu/g or ml in 77.5% of the tested samples. Higher counts (>104 cfu/g or ml) were found in 6.8% of samples including fresh-cut vegetables, cooked foods, cereals, and pastry products. To verify whether B. cereus-like isolates belonged to the B. cereus group, a PCR test targeting the sspE gene sequence specific of the group was carried out. Therefore, 174 isolates were found to be positive. Food samples were contaminated as follows: cereals (67.6%), pastry products (46.2%), cooked food (40.8%), cooked poultry meat (32.7%), seafood products (32.3%), spices (28.8%), canned products (16.7%), raw poultry meat (9.4%), fresh-cut vegetables (5.0%), and dairy products (4.8%). The 174 B. cereus isolates were characterized by partial sequencing of the panC gene, using a Sym'Previous software tool to assign them to different phylogenetic groups. Strains were distributed as follows: 61.3, 29.5, 7.5, and 1.7% in the group III, IV, II, and V, respectively. The genetic diversity was further assessed by ERIC-PCR and PFGE typing methods. PFGE and ERIC-PCR patterns analysis allowed discriminating 143 and 99 different profiles, respectivey. These findings, associated to a relatively higher prevalence of B. cereus group in different foods, could be a significant etiological agent of food in Tunisia.
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