Isolation and Genome Characterization of the Virulent Staphylococcus aureus Bacteriophage SA97

A novel bacteriophage that infects S. aureus, SA97, was isolated and characterized. The phage SA97 belongs to the Siphoviridae family, and the cell wall teichoic acid (WTA) was found to be a host receptor of the phage SA97. Genome analysis revealed that SA97 contains 40,592 bp of DNA encoding 54 predicted open reading frames (ORFs), and none of these genes were related to virulence or drug resistance. Although a few genes associated with lysogen formation were detected in the phage SA97 genome, the phage SA97 produced neither lysogen nor transductant in S. aureus. These results suggest that the phage SA97 may be a promising candidate for controlling S. aureus

Bacteriophage-Derived Endolysins Applied as Potent Biocontrol Agents to Enhance Food Safety

Endolysins, bacteriophage-encoded enzymes, have emerged as antibacterial agents that can be actively applied in food processing systems as food preservatives to control pathogens and ultimately enhance food safety. Endolysins break down bacterial peptidoglycan structures at the terminal step of the phage reproduction cycle to enable phage progeny release. In particular, endolysin treatment is a novel strategy for controlling antibiotic-resistant bacteria, which are a severe and increasingly frequent problem in the food industry. In addition, endolysins can eliminate biofilms on the surfaces of utensils. Furthermore, the cell wall-binding domain of endolysins can be used as a tool for rapidly detecting pathogens. Research to extend the use of endolysins toward Gram-negative bacteria is now being extensively conducted. This review summarizes the trends in endolysin research to date and discusses the future applications of these enzymes as novel food preservation tools in the field of food safety

Synergistic Inactivation of Bacteria Using a Combination of Erythorbyl Laurate and UV Type-A Light Treatment

This study evaluated the synergistic antimicrobial activity of erythorbyl laurate (EL) and UV type-A (UVA). To investigate the mode of synergism, changes in gene expression and bacterial inactivation activity were examined. Individual treatments with EL (10 mM) or UVA caused a 1.9- or 0.5-log CFU/ml reduction respectively, whereas EL/UVA co-treatment resulted in a 5.5-log CFU/ml reduction in Escherichia coli viable cell numbers. Similarly, treatment with either EL (2 mM) or UVA for 30 min resulted in a 2.8- or 0.1-log CFU/ml reduction in Listeria innocua, respectively, whereas combined treatment with both EL and UVA resulted in a 5.4-log CFU/ml reduction. Measurements of gene expression levels showed that EL and UVA treatment synergistically altered the gene expression of genes related to bacterial membrane synthesis/stress response. However, addition of 10-50-fold excess concentration of exogenous antioxidant compared to EL reduced the synergistic effect of EL and UVA by approximately 1 log. In summary, the results illustrate that synergistic combination of EL and UVA enhanced membrane damage independent of the oxidative stress damage induced by UVA and thus illustrate a novel photo-activated synergistic antimicrobial approach for the inactivation of both the Gram-positive and Gram-negative bacteria. Overall, this study illustrates mechanistic evaluation of a novel photochemical approach for food and environmental applications

Effect of oxidized phenolic compounds on cross-linking and properties of biodegradable active packaging film composed of turmeric and gelatin

International audienceCross-linking effects of different phenolic substances (tannic acid, caffeic acid, and green tea extract) on mechanical and barrier properties of biodegradable films consisting of turmeric (Curcuma longa) and gelatin were investigated. The results showed that degree of protein cross-linking increased with concentration of oxidized phenolic compounds, resulting in denser and stiffer film structures. Cross-link formation led to higher tensile strength and lower elongation-at-break (%), water vapor permeability, and water solubility of films with formation of aggregations. However, at high concentrations of phenolic compounds, molecular mobility increased due to grafting/branching reactions resulting in plasticizing effect. The developed films were applied as active packaging materials to fresh ground pork to extend shelf life, demonstrating good antioxidant activity and preventing lipid oxidation of fresh pork. No significant difference (p > 0.05) was noted in the overall acceptability of all samples by sensory analysis

Programmed Delay of a Virulence Circuit Promotes Salmonella Pathogenicity

To accomplish successful infection, pathogens must operate their virulence programs in a precise, time-sensitive, and coordinated manner. A major question is how pathogens control the timing of virulence gene expression during infection. Here we report that the intracellular pathogen Salmonella controls the timing and level of virulence gene expression by using an inhibitory protein, EIIANtr. A DNA binding master virulence regulator, PhoP, controls various virulence genes inside acidic phagosomes. Salmonella decreases EIIANtr amounts at acidic pH in a Lon- and PhoP-dependent manner. This, in turn, promotes expression of the PhoP-activated virulence program because EIIANtr hampers activation of PhoP-regulated genes by interfering with PhoP binding to DNA. EIIANtr enables Salmonella to impede the activation of PhoP-regulated gene expression inside macrophages. Our findings suggest that Salmonella achieves programmed delay of virulence gene activation by adjusting levels of an inhibitory factor.Signal transduction systems dictate various cellular behaviors in response to environmental changes. To operate cellular programs appropriately, organisms have sophisticated regulatory factors to optimize the signal response. The PhoP/PhoQ master virulence regulatory system of the intracellular pathogen Salmonella enterica is activated inside acidic macrophage phagosomes. Here we report that Salmonella delays the activation of this system inside macrophages using an inhibitory protein, EIIANtr (a component of the nitrogen-metabolic phosphotransferase system). We establish that EIIANtr directly restrains PhoP binding to its target promoter, thereby negatively controlling the expression of PhoP-activated genes. PhoP furthers its activation by promoting Lon-mediated degradation of EIIANtr at acidic pH. These results suggest that Salmonella ensures robust activation of its virulence system by suspending the activation of PhoP until a sufficient level of active PhoP is present to overcome the inhibitory effect of EIIANtr. Our findings reveal how a pathogen precisely and efficiently operates its virulence program during infection

Isolation and Genome Characterization of the Virulent Staphylococcus aureus Bacteriophage SA97

A novel bacteriophage that infects S. aureus, SA97, was isolated and characterized. The phage SA97 belongs to the Siphoviridae family, and the cell wall teichoic acid (WTA) was found to be a host receptor of the phage SA97. Genome analysis revealed that SA97 contains 40,592 bp of DNA encoding 54 predicted open reading frames (ORFs), and none of these genes were related to virulence or drug resistance. Although a few genes associated with lysogen formation were detected in the phage SA97 genome, the phage SA97 produced neither lysogen nor transductant in S. aureus. These results suggest that the phage SA97 may be a promising candidate for controlling S. aureus

Interactions of phenolic compounds with milk proteins

International audienceThis study showed that phenolic compounds mainly interacted with casein rather than whey protein. To prove this, the molecular interactions between phenolic compounds and milk proteins, such as casein and whey proteins, were investigated by measuring changes in their aggregate sizes of molecules. Size-exclusion chromatography was performed to determine the aggregate sizes of milk proteins. Results showed that when casein was mixed with an extract of green tea, grape, or cranberry, the aggregate size of casein increased as a result of chemical interactions between casein and the phenolic compounds. Meanwhile, only a negligible change in the aggregate size was observed when whey protein was mixed with phenolic compounds, implying little interaction. The higher affinity of these polyphenolic compounds with casein proteins was correlated with the high recovery potential of polyphenolic compounds in the cheese-making process as caseins are the main proteins in cheese curd. These results could help to design manufacturing processes of functional dairy products that improve yield and quality attributes