Nettle-Leaf Extract Derived ZnO/CuO Nanoparticle-Biopolymer-Based Antioxidant and Antimicrobial Nanocomposite Packaging Films and Their Impact on Extending the Post-Harvest Shelf Life of Guava Fruit.

Green synthesized metal oxide nanoparticles (NPs) have prominent applications in antimicrobial packaging systems. Here we have attempted for the fabrication of chitosan-based nanocomposite film containing Urtica dioica leaf extract derived copper oxide (CuO) and zinc oxide (ZnO) NPs for shelf-life extension of the packaged guava fruits. Electron microscopy and spectroscopy analysis of the CuO and ZnO NPs exhibited nano-scale size, spherical morphologies, and negative ζ-potential values. The NPs possessed appreciable antioxidant and antimicrobial activity (AMA) in order of CuO NPs > ZnO NPs >nettle extract. Therefore, this work establishes for the first time the successful synthesis of CuO NPs and compares its antimicrobial and antioxidant properties with ZnO NPs. On incorporation in chitosan, the polymer nanocomposite films were developed by solvent casting technique. The developed films were transparent, had low antioxidant but substantial AMA. The NP supplementation improved the film characteristics as evident from the decrease in moisture content, water holding capacity, and solubility of the films. The nanocomposite films improved the quality attributes and shelf life of guava fruits by one week on packaging and storage compared to unpackaged control fruits. Therefore, this study demonstrates the higher antimicrobial potential of the nettle leaf extract derived CuO/ZnO NPs for development of antimicrobial nanocomposite films as a promising packaging solution for enhancing the shelf life of various perishable fruits.

Wound dressing of chitosan-based-crosslinked gelatin/ polyvinyl pyrrolidone embedded silver nanoparticles, for targeting multidrug resistance microbes.

Wound dressing composed of chitosan, based crosslinked gelatin/ polyvinyl pyrrolidone, embedded silver nanoparticles were fabricated using solution casting method. The membrane was characterized by FTIR, SEM and TGA. Glutaraldehyde (0.5 %) was used for the crosslinking of membrane components and associated with 7-folds boosted mechanical performance, 28 % more hydrolytic stability, 3-folds thickness reduction and morphological roughness. Silver nanoparticles were characterized by UV-vis, XRD and TEM for an average size of 9.9 nm. The membrane with higher concentration of silver nanoparticles showed maximum antibacterial activity against human pathogenic bacteria; and the measured inhibition zones ranged from 1.5 to 3 cm. The activity of the particles ranged from severe to complete reduction in Penicillin, Erythromycin and Macrolide family's resistance genes expression such as ß-Lactamase, mecA and erm. This developed membrane can serve as promising and cost-effective system against severe diabetic and burn wound infections.

Genome-wide Analysis of Salmonella enterica serovar Typhi in Humanized Mice Reveals Key Virulence Features.

Salmonella enterica serovar Typhi causes typhoid fever only in humans. Murine infection with S. Typhimurium is used as a typhoid model, but its relevance to human typhoid is limited. Non-obese diabetic-scid IL2rγnull mice engrafted with human hematopoietic stem cells (hu-SRC-SCID) are susceptible to lethal S. Typhi infection. In this study, we use a high-density S. Typhi transposon library in hu-SRC-SCID mice to identify virulence loci using transposon-directed insertion site sequencing (TraDIS). Vi capsule, lipopolysaccharide (LPS), and aromatic amino acid biosynthesis were essential for virulence, along with the siderophore salmochelin. However, in contrast to the murine S. Typhimurium model, neither the PhoPQ two-component system nor the SPI-2 pathogenicity island was required for lethal S. Typhi infection, nor was the CdtB typhoid toxin. These observations highlight major differences in the pathogenesis of typhoid and non-typhoidal Salmonella infections and demonstrate the utility of humanized mice for understanding the pathogenesis of a human-specific pathogen.

Epithelial invasion by Salmonella Typhi using STIV-Met interaction.

Typhoid is a life-threatening febrile illness that affects ~24.2 million people worldwide and is caused by the intracellular bacteria Salmonella Typhi (S. Typhi). Intestinal epithelial invasion by S. Typhi is essential for the establishment of successful infection and is traditionally believed to depend on Salmonella pathogenicity island 1-encoded type 3 secretion system 1 (T3SS-1). We had previously reported that bacterial outer membrane protein T2942/STIV functions as a standalone invasin and contributes to the pathogenesis of S. Typhi by promoting epithelial invasion independent of T3SS-1 (Cell Microbiol, 2015). Here, we show that STIV, by using its 20-amino-acid extracellular loop, interacts with receptor tyrosine kinase, Met, of host intestinal epithelial cells. This interaction leads to Met phosphorylation and activation of a downstream signalling cascade, involving Src, phosphatidylinositol 3-kinase/Akt, and Rac1, which culminates into localized actin polymerisation and bacterial engulfment by the cell. Inhibition of Met tyrosine kinase activity severely limited intestinal invasion and systemic infection by S. Typhi in vivo, highlighting the importance of this invasion pathway in disease progression. This is the first report elucidating the mechanism of T3SS-1-independent epithelial invasion of S. Typhi, and this crucial host-pathogen interaction may be targeted therapeutically to restrict pathogenesis.

Assessment of microbial contaminations in commercial frozen duck meats and the application of electron beam irradiation to improve their hygienic quality.

BACKGROUND: High microbial load is a serious concern in terms of the health-related safety of products of animal origin. In this study, the microbial loads of commercial frozen duck-meat products, including bone-in whole raw, boneless sliced raw, and boneless whole smoked, were investigated for pathogenic contamination. The application of electron beam irradiation was also investigated. RESULTS: The samples revealed a serious microbial threat (102 -105 CFU g-1 for total aerobic bacteria and positive for foodborne pathogens), which required effective decontamination technology. Electron-beam irradiation (0, 1, 3, and 7 kGy) could potentially improve the hygienic quality of duck-meat samples. The D10 values for Listeria monocytogenes and Salmonella Typhi were 0.47 and 0.51 kGy, respectively. A direct epifluorescent filter technique and aerobic plate count (DEFT/APC) method was used for screening, while electron-spin resonance (ESR) spectroscopy and gas chromatography with mass spectrometry were effective as confirmatory techniques to identify radiation-induced markers in frozen duck meat. CONCLUSION: Electron-beam irradiation has the potential to ensure the microbial safety and hygienic quality of commercial duck meats. Identification of the samples for their irradiation history was also possible using radiation-induced detection markers, including the DEFT/APC, hydroxyapatite ESR radicals, and hydrocarbons. © 2018 Society of Chemical Industry.

The malS-5'UTR weakens the ability of Salmonella enterica serovar Typhi to survive in macrophages by increasing intracellular ATP levels.

Bacterial non-coding RNAs (ncRNAs), as important regulatory factors, are involved in many cellular processes, including virulence and protection against environmental stress. The 5' untranslated region (UTR) of malS (named malS-5'UTR), a regulatory ncRNA, increases the invasive capacity and influences histidine biosynthesis in Salmonella enterica serovar Typhi (S. Typhi). In this study, we found that overexpression of the malS-5'UTR decreased S. Typhi survival within macrophages. A microarray analysis of a strain overexpressing the malS-5'UTR revealed a significant increase in the mRNA levels of the atp operon. The intracellular ATP levels were elevated in the malS-5'UTR overexpression strain. Quantitative real-time polymerase chain reaction results showed that the malS-5'UTR downregulated the mRNA levels of phoP, phoQ, and mgtC. MgtC, its expression is regulated by PhoP/PhoQ two-component regulatory system, inhibits the F1F0 ATP synthase, thereby preventing the accumulation of ATP to non-physiological levels and the acidification of the cytoplasm within macrophages. Thus, we propose that the malS-5'UTR weakens the ability of S. Typhi to survive in macrophages, probably because of the accumulation of ATP within macrophages, by regulating the mRNA levels of mgtC and the atp operon in a phoP-dependent manner.

Salmonella enterica serovar Typhi siderophore production is elevated and Fur inactivation causes cell filamentation and attenuation in macrophages.

Salmonella enterica serovars Typhi and Typhimurium are two closely related bacteria causing different types of infection in humans. Iron acquisition is considered essential for virulence. Siderophores are important iron chelators and production of enterobactin and salmochelins by these serovars was quantified. Overall, Salmonella Typhi produced higher levels of siderophores than Salmonella Typhimurium. The role of the global regulator Fur, involved in iron homeostasis, present and conserved in both these serovars, was then investigated. Deletion of the fur gene led to distinct phenotypes in these serovars. Defective growth in iron-rich and iron-limiting conditions and formation of filamentous cells was only observed in the S. Typhi fur mutant. Furthermore, Fur was required for optimal motility in both serovars, but motility was more reduced for the fur mutant of S. Typhi compared to S. Typhimurium. During interaction with human-cultured macrophages, Fur was more important for S. Typhi, as the fur mutant had severe defects in uptake and survival. Globally, these results demonstrate that Fur differentially affects the physiology and the virulence phenotypes of the two strains and is more critical for S. Typhi growth, morphology, motility and interaction with host cells than it is for S. Typhimurium.

Comparing naturally occurring glycosylated forms of proline rich antibacterial peptide, Drosocin.

Antimicrobial peptides (AMPs) are key players of innate immunity. Amongst various classes of AMPs, proline rich AMPs from insects enjoy special attention with few members of this class bearing O-glycosylation as post-translational modification. Drosocin, a 19 amino acid glycosylated AMP is a member of proline rich class, synthesized in the haemolymph of Drosophila melanogaster upon bacterial challenge. We report herein the chemical synthesis of drosocin carrying disaccharide (ß-Gal(1 â†’ 3)α-GalNAc) and comparison of its structural and functional properties with another naturally occurring monoglycosylated form of drosocin i.e. α-GalNAc-drosocin as well as with non-glycosylated drosocin. The disaccharide containing drosocin exhibited lower potency compared to monoglycosylated drosocin against all the tested Gram negative bacteria, suggesting the role of the distal sugar or increase in the sugar chain length on the activity. Circular dichroism studies failed to demonstrate the differential effect of sugars on the overall peptide conformation. Haemolytic and cytotoxic properties of drosocin were not altered due to an increase in the sugar chain length. In addition, we have also evaluated the effect of differentially glycosylated drosocins on two pro-inflammatory cytokines secreted by murine macrophages or LPS stimulated macrophages. All the drosocin forms tested, neither could stimulate the secretion of TNF-α and IL-6 nor could modulate LPS-induced levels of TNF-α and IL-6 in murine macrophages. This study provides insights about naturally occurring two different glycosylated forms of drosocin.

QseB mediates biofilm formation and invasion in Salmonella enterica serovar Typhi.

QseB is a response regulator of the QseBC two-component system (TCS) which is associated with quorum sensing and functions as a global regulator of flagella, biofilm formation, and virulence. The function of QseB and its interaction with QseC has been the subject of study in some organisms, however, little work was done in Salmonella enterica serovar Typhi (S. Typhi). The objective of this study was to investigate the effect of QseB on biofilm formation and virulence in S. Typhi. It showed that the biofilm formation ability of qseC mutant was limited as compared to the wild type strain. We also show overexpression of qseB was in a qseC mutant. Interestingly, deletion of qseB in a qseC mutant restored a wild type phenotype. These results suggested that QseB may account for the impaired biofilm formation in the absence of QseC. Furthermore, deletion of qseB in wild type cells decreased biofilm formation, whereas overexpression of qseB in wild type cells increased biofilm formation. Quantitative real-time PCR also revealed the up-regulation of some fimbria-associated genes in a qseB overexpression strain. These results indicate that QseB may enhance biofilm formation in the presence of QseC. Taken together, we hypothesize that QseB has dual regulatory functions which are dependent upon its cognate sensor. Additionally, invasion of HeLa cells was enhanced in qseB mutant but attenuated in a qseC mutant compared with wild-type. The ß-galactosidase activity of invF::lacZ was increased in qseB mutant but decreased in qseC mutant which was consistent with invasion results. In conclusion, QseB may have dual regulatory functions concerning biofilm formation and plays a negative role in virulence of S. Typhi.

Toxicity mechanism of titanium dioxide and zinc oxide nanoparticles against food pathogens.

Food preservation is an important field of research. It extends the shelf life of major food products. Our current study is based on food preservation through TiO2 and ZnO nanoparticles. TiO2 and ZnO are biocompatible nanomaterial. The biocompatibility of the materials were established through toxicity studies on cell lines. Titanium dioxide and Zinc Oxide nanoparticle were synthesized by wet chemical process. They are characterized by X-Ray diffraction and TEM. The antibacterial activities of both the materials were analysed to ensure their effectiveness as food preservative against Salmonella typhi, Klebsiella pneumoniae and Shigella flexneri. The results indicates that TiO2 and ZnO nanoparticle inhibits Salmonella, Klebsiella and Shigella. The mode of action is by the generation of ROS in cases of Salmonella, Klebsiella. Mode of action in Shigella is still unclear. It was also proved that TiO2 and ZnO nanoparticle are biocompatible materials.

Mechanisms of Salmonella Typhi Host Restriction.

Salmonella enterica serovar Typhi (S. Typhi) is the cause of typhoid fever, a life-threatening bacterial infection that is very common in the developing world. Recent spread of antimicrobial resistant isolates of S. Typhi makes typhoid fever, a global public health risk. Despite being a common disease, still very little is known about the molecular mechanisms underlying typhoid fever and S. Typhi pathogenesis. In contrast to other Salmonellae, S. Typhi can only infect humans. The molecular bases of this human restriction are mostly unknown. Recent studies identified a novel pathway that contributes to S. Typhi human restriction and is required for killing S. Typhi in macrophages of nonsusceptible species. The small Rab GTPase Rab32 and its guanine nucleotide exchange factor BLOC-3 are the critical components of this pathway. These proteins were already well known as important regulators of intracellular membrane transport. In particular, they are central for the transport of enzymes that synthetize melanin in pigment cells. The recent findings that Rab32 and BLOC-3 are required for S. Typhi host restriction point out to a novel mechanism restricting the growth of bacterial pathogen, dependent on the transport of still unknown molecule(s) to the S. Typhi vacuole. The identification of this novel antimicrobial pathway constitutes a critical starting point to study molecular mechanisms killing bacterial pathogens and possibly identify novel antimicrobial molecules.

What proportion of Salmonella Typhi cases are detected by blood culture? A systematic literature review.

Blood culture is often used in definitive diagnosis of typhoid fever while, bone marrow culture has a greater sensitivity and considered reference standard. The sensitivity of blood culture measured against bone marrow culture results in measurement bias because both tests are not fully sensitive. Here we propose a combination of the two cultures as a reference to define true positive S. Typhi cases. Based on a systematic literature review, we identified ten papers that had performed blood and bone marrow culture for S. Typhi in same subjects. We estimated the weighted mean of proportion of cases detected by culture measured against true S. Typhi positive cases using a random effects model. Of 529 true positive S. Typhi cases, 61 % (95 % CI 52-70 %) and 96 % (95 % CI 93-99 %) were detected by blood and bone marrow cultures respectively. Blood culture sensitivity was 66 % (95 % CI 56-75 %) when compared with bone marrow culture results. The use of blood culture sensitivity as a proxy measure to estimate the proportion of typhoid fever cases detected by blood culture is likely to be an underestimate. As blood culture sensitivity is used as a correction factor in estimating typhoid disease burden, epidemiologists and policy makers should account for the underestimation.

Antioxidant Defense by Thioredoxin Can Occur Independently of Canonical Thiol-Disulfide Oxidoreductase Enzymatic Activity.

The thiol-disulfide oxidoreductase CXXC catalytic domain of thioredoxin contributes to antioxidant defense in phylogenetically diverse organisms. We find that although the oxidoreductase activity of thioredoxin-1 protects Salmonella enterica serovar Typhimurium from hydrogen peroxide in vitro, it does not appear to contribute to Salmonella's antioxidant defenses in vivo. Nonetheless, thioredoxin-1 defends Salmonella from oxidative stress resulting from NADPH phagocyte oxidase macrophage expression during the innate immune response in mice. Thioredoxin-1 binds to the flexible linker, which connects the receiver and effector domains of SsrB, thereby keeping this response regulator in the soluble fraction. Thioredoxin-1, independently of thiol-disulfide exchange, activates intracellular SPI2 gene transcription required for Salmonella resistance to both reactive species generated by NADPH phagocyte oxidase and oxygen-independent lysosomal host defenses. These findings suggest that the horizontally acquired virulence determinant SsrB is regulated post-translationally by ancestrally present thioredoxin.

SufC may promote the survival of Salmonella enterica serovar Typhi in macrophages.

The sufC gene of Escherichia coli (E. coli) is required for the biogenesis of iron-sulfur (Fe-S) cluster under oxidative stress conditions. In order to investigate the roles of sufC in Salmonella enterica serovar Typhi (S. Typhi), isogenic S. Typhi strain GIFU10007 harboring a non-polar mutation of sufC (ΔsufC) was constructed and the results showed that the sufC deleted mutant grew more slowly than the wild type strain when encounter oxidative stresses. Moreover, the deletion of sufC gene decreased S. Typhi survival within macrophages. After macrophages infected by sufC deleted mutant and wild type strain, we detected IL-6 and TNF-α released into the supernatant, and found the expression of IL-6 and TNF-α decreased in the supernatant of sufC deleted mutant infected groups than the wild type strain infected ones. In summary, our results showed that SufC may promote S. Typhi coping oxidative stress and help S. Typhi survival in macrophages.

Inhibition of Salmonella enterica biofilm formation using small-molecule adenosine mimetics.

Biofilms have been widely implicated in chronic infections and environmental persistence of Salmonella enterica, facilitating enhanced colonization of surfaces and increasing the ability of the bacteria to be transmitted to new hosts. Salmonella enterica serovar Typhi biofilm formation on gallstones from humans and mice enhances gallbladder colonization and bacterial shedding, while Salmonella enterica serovar Typhimurium biofilms facilitate long-term persistence in a number of environments important to food, medical, and farming industries. Salmonella regulates expression of many virulence- and biofilm-related processes using kinase-driven pathways. Kinases play pivotal roles in phosphorylation and energy transfer in cellular processes and possess an ATP-binding pocket required for their functions. Many other cellular proteins also require ATP for their activity. Here we test the hypothesis that pharmacological interference with ATP-requiring enzymes utilizing adenosine mimetic compounds would decrease or inhibit bacterial biofilm formation. Through the screening of a 3,000-member ATP mimetic library, we identified a single compound (compound 7955004) capable of significantly reducing biofilm formation by S. Typhimurium and S. Typhi. The compound was not bactericidal or bacteriostatic toward S. Typhimurium or cytotoxic to mammalian cells. An ATP-Sepharose affinity matrix technique was used to discover potential protein-binding targets of the compound and identified GroEL and DeoD. Compound 7955004 was screened against other known biofilm-forming bacterial species and was found to potently inhibit biofilms of Acinetobacter baumannii as well. The identification of a lead compound with biofilm-inhibiting capabilities toward Salmonella provides a potential new avenue of therapeutic intervention against Salmonella biofilm formation, with applicability to biofilms of other bacterial pathogens.

Production of prodigiosin using tannery fleshing and evaluating its pharmacological effects.

AIM: The focal theme of present investigation includes isolation of prodigiosin producing fish gut bacteria, enhancing its production using tannery solid waste fleshing, and evaluation of its pharmacological effect. METHODS: Optimization of fermentation conditions to yield maximum prodigiosin, and instrumental analysis using FTIR, NMR, ESI-MS, TGA, and DSC. RESULTS: The optimum conditions required for the maximum prodigiosin concentration were achieved at time 30 h, temperature 30°C, pH 8, and 3% substrate concentration. The secondary metabolite was analyzed using ESI-MS, FTIR, and NMR. Therapeutic efficacy was assessed by in vitro anticancer studies. Among the pathogenic bacteria Pseudomonas aeruginosa was most susceptible at the lowest concentration followed by Salmonella typhi. IC50 concentration was cell line specific (HeLa cells: 4.3 µM, HEp2: 5.2 µM, and KB cells: 4.8 µM) and remains nontoxic up to the concentration of 25 µM on normal Vero cells suggesting that cancerous cells are more susceptible to the prodigiosin at lower concentration. CONCLUSION: Maximum prodigiosin production was obtained with tannery fleshing. The potency of the fish gut bacterial secondary metabolite prodigiosin as a therapeutic agent was confirmed through in vitro antimicrobial and anticancer studies.

Evaluation of antioxidant and antimicrobial activities of essential oils from Carum copticum seed and Ferula assafoetida latex.

UNLABELLED: Carum copticum and Ferula assafoetida have several medicinal properties including antispasmodic, carminative, sedative, analgesic, and antiseptic. Reactive oxygen species (ROS), reactive nitrogen species (RNS), hydrogen peroxide (H(2) O(2) ), and thiobarbituric acid reactive substances (TBARS) scavenging activities of Carum and Ferula oils along with their antibacterial and antifungal activities were examined. Thymol (40.25%), γ-terpinene (38.7%) and p-cymene (15.8%) were detected as the main components of Carum oil while, ß-pinene (47.1%), α-pinene (21.36%), and 1, 2-dithiolane (18.6%) were the main components of Ferula oil. Inhibitory concentrations (IC50) for total radical scavenging were between 40 and 60 and 130 and 160 µg/mL of Carum and Ferula oil, respectively. Minimal inhibitory concentration (MIC) for Salmonella typhi, Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Aspergillus niger, and Candida albicans were 78 ± 8, 65 ± 7, 14 ± 3, 5 ± 2, 5.6 ± 1.3, and 8.8 ± 2.2 µg/mL of Carum oil, respectively. MIC for S. typhi, E. coli, S. aureus, B. subtilis, A. niger, and C. albicans were >200, >200, 125 ± 17, 80 ± 12, 85 ± 5, and 90 ± 11 µg/mL of Ferula oil, respectively. Accordingly, Carum and Ferula oils could be used as safe and effective natural antioxidants to improve the oxidative stability of fatty foods during storage and to preserve foods against food burn pathogens. PRACTICAL APPLICATION: This study clearly demonstrates the potential of Carum and Ferula oil especially Carum oil as natural antioxidant and antimicrobial agent. The chemical composition of essential oils was identified. Thus, identification of such compounds also helps to discover of new antioxidant, antibacterial and antifungal agents for potential applications in food safety and food preservation.

Role of the Salmonella enterica serovar Typhi Fur regulator and small RNAs RfrA and RfrB in iron homeostasis and interaction with host cells.

Iron is an essential element but can be toxic at high concentrations. Therefore, its acquisition and storage require tight control. Salmonella encodes the global regulator Fur (ferric uptake regulator) and the small regulatory non-coding RNAs (sRNAs) RfrA and RfrB, homologues of RyhB. The role of these iron homeostasis regulators was investigated in Salmonella enterica serovar Typhi (S. Typhi). Strains containing either single or combined deletions of these regulators were obtained. The mutants were tested for growth in low and high iron conditions, resistance to oxidative stress, expression and production of siderophores, and during interaction with host cells. The fur mutant showed a growth defect and was sensitive to hydrogen peroxide. The expression of the sRNAs was responsible for these defects. Siderophore expression by S. Typhi and both sRNAs were regulated by iron and by Fur. Fur contributed to invasion of epithelial cells, and was shown for the first time to play a role in phagocytosis and intracellular survival of S. Typhi in human macrophages. The sRNAs RfrA and RfrB were not required for interaction with epithelial cells, but both sRNAs were important for optimal intracellular replication in macrophages. In S. Typhi, Fur is a repressor of both sRNAs, and loss of either RfrA or RfrB resulted in distinct phenotypes, suggesting a non-redundant role for these regulatory RNAs.

Curcumin reduces the antimicrobial activity of ciprofloxacin against Salmonella typhimurium and Salmonella typhi.

OBJECTIVES: Typhoidal and non-typhoidal infection by Salmonella is a serious threat to human health. Ciprofloxacin is the last drug of choice to clear the infection. Ciprofloxacin, a gyrase inhibitor, kills bacteria by inducing chromosome fragmentation, SOS response and reactive oxygen species (ROS) in the bacterial cell. Curcumin, an active ingredient from turmeric, is a major dietary molecule among Asians and possesses medicinal properties. Our research aimed at investigating whether curcumin modulates the action of ciprofloxacin. METHOD: We investigated the role of curcumin in interfering with the antibacterial action of ciprofloxacin in vitro and in vivo. RT-PCR, DNA fragmentation and confocal microscopy were used to investigate the modulation of ciprofloxacin-induced SOS response, DNA damage and subsequent filamentation by curcumin. Chemiluminescence and nitroblue tetrazolium reduction assays were performed to assess the interference of curcumin with ciprofloxacin-induced ROS. DNA binding and cleavage assays were done to understand the rescue of ciprofloxacin-mediated gyrase inhibition by curcumin. RESULTS: Curcumin interferes with the action of ciprofloxacin thereby increasing the proliferation of Salmonella Typhi and Salmonella Typhimurium in macrophages. In a murine model of typhoid fever, mice fed with curcumin had an increased bacterial burden in the reticuloendothelial system and succumbed to death faster. This was brought about by the inhibition of ciprofloxacin-mediated downstream signalling by curcumin. CONCLUSIONS: The antioxidant property of curcumin is crucial in protecting Salmonella against the oxidative burst induced by ciprofloxacin or interferon γ (IFNγ), a pro-inflammatory cytokine. However, curcumin is unable to rescue ciprofloxacin-induced gyrase inhibition. Curcumin's ability to hinder the bactericidal action of ciprofloxacin and IFNγ might significantly augment Salmonella pathogenesis.

Salmonella enterica serovar Typhi plasmid pR ST98 enhances intracellular bacterial growth and S. typhi-induced macrophage cell death by suppressing autophagy.

OBJECTIVES: Plasmid pR ST98 is a hybrid resistance-virulence plasmid isolated from Salmonella enterica serovar Typhi (S. typhi). Previous studies demonstrated that pR ST98 could enhance the virulence of its host bacteria. However, the mechanism of pR ST98-increased bacterial virulence is still not fully elucidated. This study was designed to gain further insight into the roles of pR ST98 in host responses. METHODS: Human-derived macrophage-like cell line THP-1 was infected with wild-type (ST8), pR ST98-deletion (ST8-ΔpR ST98), and complemented (ST8-c-pR ST98) S. typhi strains. Macrophage autophagy was performed by extracting the membrane-unbound LC3-I protein from cells, followed by flow cytometric detection of the membrane-associated fraction of LC3-II. Intracellular bacterial growth was determined by colony-forming units (cfu) assay. Macrophage cell death was measured by flow cytometry after propidium iodide (PI) staining. Autophagy activator rapamycin (RAPA) was added to the medium 2 h before infection to investigate the effect of autophagy on intracellular bacterial growth and macrophage cell death after S. typhi infection. RESULTS: Plasmid pR ST98 suppressed autophagy in infected macrophages and enhanced intracellular bacterial growth and S. typhi-induced macrophage cell death. Pretreatment with RAPA effectively restricted intracellular bacterial growth of ST8 and ST8-c-pR ST98, and alleviated ST8 and ST8-c-pR ST98-induced macrophage cell death, but had no significant effect on ST8-ΔpR ST98. CONCLUSIONS: Plasmid pR ST98 enhances intracellular bacterial growth and S. typhi-induced macrophage cell death by suppressing autophagy.