Tumour necrosis factor alpha mediated apoptosis in murine macrophages by Salmonella enterica serovar Typhi under oxidative stress

Potential probiotic Lactiplantibacillus plantarum strains alleviate TNF-α by regulating ADAM17 protein and ameliorate gut integrity through tight junction protein expression in in vitro model

BACKGROUND

Lactiplantibacillus species are extensively studied for their ability to regulate host immune responses and functional therapeutic potentials. Nevertheless, there is a lack of understanding on the mechanisms of interactions with the hosts during immunoregulatory activities.

METHODS

Two Lactiplantibacillus plantarum strains MKMB01 and MKMB02 were tested for probiotic potential following Indian Council of Medical Research (ICMR) guidelines. Human colorectal adenocarcinoma cells such as HT-29, caco-2, and human monocytic cell THP-1 were also used to study the potential of MKMB01 and MKMB02 in regulating the host immune response when challenged with enteric pathogen Salmonella enterica typhimurium. Cells were pre-treated with MKMB01 and MKMB02 for 4 h and then stimulated with Salmonella. qRT-PCR and ELISA were used to analyze the genes and protein expression. Confocal microscopy and field emission scanning electron microscopy (FESEM) were used to visualize the effects. An Agilent Seahorse XF analyzer was used to determine real-time mitochondrial functioning.

RESULTS

Both probiotic strains could defend against Salmonella by maintaining gut integrity via expressing tight junction proteins (TJPs), MUC-2, and toll-like receptors (TLRs) negative regulators such as single Ig IL-1-related receptor (SIGIRR), toll-interacting protein (Tollip), interleukin-1 receptor-associated kinase (IRAK)-M, A20, and anti-inflammatory transforming growth factor-β and interleukin-10. Both strains also downregulated the expression of pro-inflammatory cytokines/chemokines interleukin-1β, monocyte chemoattractant protein (MCP)-1, tumor necrosis factor-alpha (TNF-α), interleukin 6, and nitric oxide (NO). Moreover, TNF-α sheddase protein, a disintegrin and metalloproteinase domain 17 (ADAM17), and its regulator iRhom2 were downregulated by both strains. Moreover, the bacteria also ameliorated Salmonella-induced mitochondrial dysfunction by restoring bioenergetic profiles, such as non-mitochondrial respiration, spare respiratory capacity (SRC), basal respiration, adenosine triphosphate (ATP) production, and maximal respiration.

CONCLUSIONS

MKMB01 and MKMB02 can reduce pathogen-induced gut-associated disorders and therefore should be further explored for their probiotic potential.

Peripheral inflammation as a potential mechanism and preventive strategy for perioperative neurocognitive disorder under general anesthesia and surgery

General anesthesia, as a commonly used medical intervention, has been widely applied during surgical procedures to ensure rapid loss of consciousness and pain relief for patients. However, recent research suggests that general anesthesia may be associated with the occurrence of perioperative neurocognitive disorder (PND). PND is characterized by a decline in cognitive function after surgery, including impairments in attention, memory, learning, and executive functions. With the increasing trend of population aging, the burden of PND on patients and society's health and economy is becoming more evident. Currently, the clinical consensus tends to believe that peripheral inflammation is involved in the pathogenesis of PND, providing strong support for further investigating the mechanisms and prevention of PND.

Defying the odds: Determinants of the antimicrobial response of Salmonella Typhi and their interplay

Salmonella Typhi, the invasive serovar of S. enterica subspecies enterica, causes typhoid fever in healthy human hosts. The emergence of antibiotic-resistant strains has consistently challenged the successful treatment of typhoid fever with conventional antibiotics. Antimicrobial resistance (AMR) in Salmonella is acquired either by mutations in the genomic DNA or by acquiring extrachromosomal DNA via horizontal gene transfer. In addition, Salmonella can form a subpopulation of antibiotic persistent (AP) cells that can survive at high concentrations of antibiotics. These have reduced the effectiveness of the first and second lines of antibiotics used to treat Salmonella infection. The recurrent and chronic carriage of S. Typhi in human hosts further complicates the treatment process, as a remarkable shift in the immune response from pro-inflammatory Th1 to anti-inflammatory Th2 is observed. Recent studies have also highlighted the overlap between AP, persistent infection (PI) and AMR. These incidents have revealed several areas of research. In this review, we have put forward a timeline for the evolution of antibiotic resistance in Salmonella and discussed the different mechanisms of the same availed by the pathogen at the genotypic and phenotypic levels. Further, we have presented a detailed discussion on Salmonella antibiotic persistence (AP), PI, the host and bacterial virulence factors that can influence PI, and how both AP and PI can lead to AMR.

Potential of 1-(1-napthylmethyl)-piperazine, an efflux pump inhibitor against cadmium-induced multidrug resistance in Salmonella enterica serovar Typhi as an adjunct to antibiotics

This study was focused on elucidating inhibition of antibiotic efflux mechanism of cadmium adapted (CdA) Salmonella Typhi Ty2 cells. Herein, upregulated expression of efflux genes (acrB, tolC) and their regulators (soxS, marA) was observed in CdA Ty2 cells by qRT-PCR. The pathogen further elevated the expression of these genes even in the presence of three efflux pump inhibitors (EPIs), i.e., Phe-Arg-β-naphthylamide, 1-(1-naphthyl-methyl)piperazine, and 5-hydroxy-2-methyl-1,4-naphthoquinone, perhaps by sensing the pressure of the latter in addition to cadmium stress. Interaction of different EPIs with efflux pumps of CdA Ty2 cells was confirmed using ethidium bromide (EtBr) accumulation and efflux assay. All the EPIs could cause retention of EtBr which was indicated by increased fluorescence units. Considering this potential of EPIs, retention of antibiotics was evaluated in CdA Ty2 cells wherein EPIs were used in combination with selected antibiotics (instead of EtBr). A decrease in the effective concentration of antibiotics was observed. This was further validated using the clinical isolates. The data revealed the efficiency of EPIs as they could inhibit the efflux potential of even the overexpressed efflux pumps. Thus, combination of EPI(s)-antibiotics may be exploited in future as one of the strategies for combating metal induced antibiotic resistance.

Prophylactic potential of cytolethal distending toxin B (CdtB) subunit of typhoid toxin against Typhoid fever

Typhoid fever caused by Salmonella enterica serovar Typhi (S.Typhi) continues to be a major problem, especially in developing countries. Due to the rapid emergence of multi-drug-resistant (MDR) strains, which limits the efficacy of conventional antibiotics as well as problems associated with the existing vaccines, efforts are being made to develop effective prophylactic agents. CdtB subunit of typhoid toxin was selected for assessing its vaccine potential due to its high conservation throughout the Typhi strains. In-vitro assessment of DNase activity of cloned and purified CdtB protein showed a significant decrease in the band intensity of DNA. The measure of metabolic activity and morphological alterations assessed using different cell lines in the presence of CdtB protein showed no significant signs of toxicity. These observations were further strengthened by cell cycle analysis, assessed by flow cytometry. Keeping these observations in mind, the immunoprotective potential of CdtB was assessed using S.Typhi induced mouse peritonitis model. A significant titer of IgG antibodies (>128000) against CdtB protein was recorded in the immunized mice by enzyme-linked immunosorbent assay (ELISA), which was also validated by immunoblotting. Active immunization with the protein protected 75% mice against a lethal dose of S.Typhi Ty2. The data indicated a significant (up to 5 log) reduction in the bacterial load in the spleen and liver of immunized-infected mice compared to control (unimmunized-infected) mice which might have resulted in the modulation of histoarchitecture of spleen and liver and the levels of cytokines (IL-6, TNF-α and IL-10) production; thereby indicating the effectiveness of the subunit. The observations deduced from the study give the proof of concept of immunogenic potential of protein. However, further studies involving the immunoreactivity of CdtB with the statistically significant number of sera samples obtained from the human patients would be helpful in establishing the relevance of CdtB protein in humans and for making the strategies to develop it as an effective vaccine candidate.

TNFR1 and TNFR2 in the Control of the Life and Death Balance of Macrophages

Macrophages stand in the first line of defense against a variety of pathogens but are also involved in the maintenance of tissue homeostasis. To fulfill their functions macrophages sense a broad range of pathogen- and damage-associated molecular patterns (PAMPs/DAMPs) by plasma membrane and intracellular pattern recognition receptors (PRRs). Intriguingly, the overwhelming majority of PPRs trigger the production of the pleiotropic cytokine tumor necrosis factor-alpha (TNF). TNF affects almost any type of cell including macrophages themselves. TNF promotes the inflammatory activity of macrophages but also controls macrophage survival and death. TNF exerts its activities by stimulation of two different types of receptors, TNF receptor-1 (TNFR1) and TNFR2, which are both expressed by macrophages. The two TNF receptor types trigger distinct and common signaling pathways that can work in an interconnected manner. Based on a brief general description of major TNF receptor-associated signaling pathways, we focus in this review on research of recent years that revealed insights into the molecular mechanisms how the TNFR1-TNFR2 signaling network controls the life and death balance of macrophages. In particular, we discuss how the TNFR1-TNFR2 signaling network is integrated into PRR signaling.

Inhibitory Effects of Antimicrobial Peptide JH-3 on Salmonella enterica Serovar Typhimurium Strain CVCC541 Infection-Induced Inflammatory Cytokine Release and Apoptosis in RAW264.7 Cells

The antibiotic resistance of Salmonella has become increasingly serious due to the increased use of antibiotics, and antimicrobial peptides have been considered as an ideal antibiotic alternative. Salmonella can induce macrophage apoptosis and thus further damage the immune system. The antimicrobial peptide JH-3 has been shown to have a satisfactory anti-Salmonella effect in previous research, but its mechanism of action remains unknown. In this study, the effects of JH-3 on macrophages infected with Salmonella Typhimurium CVCC541 were evaluated at the cellular level. The results showed that JH-3 significantly alleviated the damage to macrophages caused by S. Typhi infection, reduced the release of lactic dehydrogenase (LDH), and killed the bacteria in macrophages. In addition, JH-3 decreased the phosphorylation level of p65 and the expression and secretion of interleukin 2 (IL-2), IL-6, and tumor necrosis factor-α (TNF-α) by inhibiting the activation of the mitogen-activated protein kinase (MAPK) (p38) signaling pathway and alleviating the cellular inflammatory response. From confocal laser scanning microscopy and flow cytometry assays, JH-3 was observed to inhibit the release of cytochrome c in the cytoplasm; the expression of TNF-αR2, caspase-9, and caspase-8; to further weaken caspase-3 activation; and to reduce the S.-Typhi-induced apoptosis of macrophages. In summary, the mechanism by which JH-3 inhibits Salmonella infection was systematically explored at the cellular level, laying the foundation for the development and utilization of JH-3 as a therapeutic alternative to antibiotics.

Augmented antibiotic resistance associated with cadmium induced alterations in Salmonella enterica serovar Typhi

In view of the reports on co-selection of metal and antibiotic resistance, recently we have reported that increased cadmium accumulation in Salmonella Typhi Ty2 leads to increased antibiotic resistance. In continuation, the present study was carried to substantiate this association in clinical isolates. Interestingly, the levels of cadmium were found to be more in the clinical isolates which co-related with their antibiotic sensitivity/resistance pattern. On cadmium accumulation, antibiotic(s) sensitive isolates were rendered resistant and the resistant isolates were rendered more resistant as per their minimum inhibitory concentration(s). Further, after subjecting the pathogen to cadmium accumulation, alterations occurring in the cells were assessed. Transgenerational cadmium exposure led to changes in growth response, morphology, proteome, elevated antioxidants other than SOD, increased biofilm formation, decreased intracellular macrophage killing coupled with upregulation of genes encoding metallothionein and metal transporters. Thus, these results indicate that cadmium, if acquired from the environment, being non-degradable can exert a long-lasting selective pressure on Salmonella in the host which may display antibiotic resistance later on, as a result of co-selection. Therefore, appropriate strategies need to be developed to inhibit such an enduring pressure of heavy metals, as these represent one of the factors for the emerging antibiotic resistance in pathogens.

Remediation of intramacrophageal Shigella dysenteriae type 1 by probiotic lactobacilli isolated from human infants' stool samples

Background & objectives:

Shigella dysenteriae is one of the most virulent pathogens causing bacillary dysentery and is responsible for high mortality in infants. To reduce the load of antibiotic therapy for treating shigellosis, this study was carried out to assess the ex vivo effect of novel probiotic lactobacilli, isolated from infant's stool samples, on killing S. dysenteriae type 1 residing in the rat macrophages.

Methods:

Stool samples from infants were collected, processed for the isolation of lactobacilli and screened for the probiotic attributes (acid tolerance, bile tolerance, ability to adhere intestinal cells and anti-S. dysenteriae activity). The effect of cell-free supernatant of lactobacilli on Shigella- infected macrophages in terms of phagocytic ability, extent of lipid peroxidation, nitrite, superoxide dismutase and glutathione levels was evaluated.

Results:

Based on the probiotic attributes, three lactobacilli were isolated from the stool samples of infants. Using classical and molecular tools, these isolates were identified as Lactobacillus pentosus, L. Paraplantarum and L. rhamnosus. All the three lactobacilli had the ability to kill intramacrophage S. dysentriae type 1. The anti-Shigella activity of the probiotic lactobacilli was attributed to increased antioxidative ability and decreased free radical production by the infected macrophages.

Interpretation & conclusions:

Probiotic cocktail of L. pentosus, L. paraplantarum and L. rhamnosus showed ex vivo killing of S. dysenteriae residing inside the rat macrophages significantly. This cocktail has the potential to be used as a natural alternative for treating S. dysenteriae infection, especially in infants, however, further studies need to be done to confirm these finding in vivo.

Potential of 2, 2'-dipyridyl diselane as an adjunct to antibiotics to manage cadmium-induced antibiotic resistance in Salmonella enterica serovar Typhi Ty2 strain

One of the reasons for increased antibiotic resistance in Salmonella enterica serovar Typhi Ty2 is the influx of heavy metal ions in the sewage, from where the infection is transmitted. Therefore, curbing these selective agents could be one of the strategies to manage the emergence of multidrug resistance in the pathogen. As observed in our earlier study, the present study also confirmed the links between cadmium accumulation and antibiotic resistance in Salmonella. Therefore, the potential of a chemically-synthesised compound 2, 2'-dipyridyl diselane (DPDS) was explored to combat the metal-induced antibiotic resistance. Its metal chelating and antimicrobial properties were evidenced by fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and microbroth dilution method. Owing to these properties of DPDS, further, this compound was evaluated for its potential to be used in combination with conventional antibiotics. The data revealed effective synergism at much lower concentrations of both the agents. Thus, it is indicated from the study that the combination of these two agents at their lower effective doses might reduce the chances of emergence of antibiotic resistance, which can be ascribed to the multi-pronged action of the agents.

Immunomodulatory and antimicrobial efficacy of Lactobacilli against enteropathogenic infection of Salmonella typhi: In-vitro and in-vivo study

Salmonellosis-induced diarrhea, is one of the commonest cause of childhood mortality in developing countries. Using of probiotics is viewed as a promising means for reducing the pathogenic loads of bacterial infection. The current study aimed to evaluate the potential antimicrobial and immunomodulatory efficacy of isolated lactobacillus strains against the enteropathogenic effect of S. Typhi. Different Lactobacillus strains were isolated from 13 dairy products. Their antimicrobial activities were tested against different bacterial strains. Six groups of CD1 mice were treated for 8 days as follows: group (1) untreated control; group (2) was challenged with single inoculation S. typhi, and groups (3) and (4) were treated with Lactobacillus plantarum (LA5) or Lactobacillus paracsi (LA7) for 7 days, respectively. Groups (5) and (6) were challenged with S. typhi, and then treated with either LA5 or LA 7 for 7 days, respectively. Isolated Lactobacillus showed antimicrobial activity against wide range of bacterial strains. Salmonellosis showed high widal titer, induced significant disturbance of TNF and IL-1β, while sever changes of the histological patterns of the intestinal villi and hepatocytes have been illustrated. LA5 or LA7 succeeded to eradicate typhoid infection, restore the values of inflammatory cytokines to typical levels of control group, and improve histological pictures of intestinal and hepatic tissues. It can be concluded that lactobacilli are promising candidate in protection and eradication against bacterial infection induced by S. Typhi due to its antimicrobial, anti-inflammatory, and immunomodulatory activities.

Tissue-specific Salmonella Typhimurium gene expression during persistence in pigs

Salmonellosis caused by Salmonella Typhimurium is one of the most important bacterial zoonotic diseases. The bacterium persists in pigs resulting in asymptomatic 'carrier pigs', generating a major source for Salmonella contamination of pork. Until now, very little is known concerning the mechanisms used by Salmonella Typhimurium during persistence in pigs. Using in vivo expression technology (IVET), a promoter-trap method based on ΔpurA attenuation of the parent strain, we identified 37 Salmonella Typhimurium genes that were expressed 3 weeks post oral inoculation in the tonsils, ileum and ileocaecal lymph nodes of pigs. Several genes were expressed in all three analyzed organs, while other genes were only expressed in one or two organs. Subsequently, the identified IVET transformants were pooled and reintroduced in pigs to detect tissue-specific gene expression patterns. We found that efp and rpoZ were specifically expressed in the ileocaecal lymph nodes during Salmonella peristence in pigs. Furthermore, we compared the persistence ability of substitution mutants for the IVET-identified genes sifB and STM4067 to that of the wild type in a mixed infection model. The ΔSTM4067::kanR was significantly attenuated in the ileum contents, caecum and caecum contents and faeces of pigs 3 weeks post inoculation, while deletion of the SPI-2 effector gene sifB did not affect Salmonella Typhimurium persistence. Although our list of identified genes is not exhaustive, we found that efp and rpoZ were specifically expressed in the ileocaecal lymph nodes of pigs and we identified STM4067 as a factor involved in Salmonella persistence in pigs. To our knowledge, our study is the first to identify Salmonella Typhimurium genes expressed during persistence in pigs.

Catechin suppresses an array of signalling molecules and modulates alcohol-induced endotoxin mediated liver injury in a rat model

Induction of nuclear factor kappa B (NF-κB)-mediated gene expression has been implicated in the pathogenesis of alcoholic liver disease through enhanced production of reactive oxygen species and pro-inflammatory mediators. The present study was carried out to investigate the role of catechin as a chain breaking inhibitor against experimental alcoholic liver injury. Rats were administered 35% v/v ethanol orally at a dose of 10 g/Kg/day for two weeks, followed by 14 g/Kg/day for 10 weeks. Catechin (50 mg/Kg) was co-supplemented after 4 weeks of alcohol treatment till the end of the dosing period. Following chronic alcohol exposure, rats developed endotoxemia and severe pathological changes in the liver such as pronounced fatty change, vacuolar degeneration and inflammation. These changes were accompanied by activation of NF-κB and induction of inflammatory and cytotoxic mediators leading to increased level of tumor necrosis factor-alpha, enhanced formation of malondialdehyde in the liver followed by drastic alterations in the hepatic antioxidant defense systems. Additionally, nitrite levels and lactate dehydrogenase activities were also significantly elevated on chronic alcohol consumption. Alcohol exposure also increased the number of micronucleated cells indicating that alcohol abuse may again be associated with the nuclear changes. Supplementation with catechin ameliorated the alcohol-induced liver injury by downregulating the endotoxin-mediated activation of initial signalling molecule NF-κB and further going downstream the signalling cascade including tumor necrosis factor-alpha, nitric oxide and reactive oxygen species and by enhancing the antioxidant profile. These observations correlated well with the histological findings. Moreover, a remarkable decrease in the percentage of micronucleated cells was observed with catechin supplementation indicating an apparent protection against alcohol-induced toxicity. These findings suggest that catechin may alleviate experimental alcoholic liver disease by suppressing induction of NF-κB, a key component of signalling pathway, thus forming a pharmacological basis for designing novel therapeutic agents against alcohol induced endotoxin-mediated liver injury.

Effect of L. plantarum cell-free extract and co-trimoxazole against Salmonella Typhimurium: a possible adjunct therapy

Background

Frequent and indiscriminate use of antibiotics has led to the development of multi-drug resistant bacterial strains. It necessitates the exploitation of alternative therapeutic strategies. In order to reduce the dose of antibiotic required and to decrease the associated side effects, the present study was aimed at evaluating the synergism, if any, between a conventional antibiotic, co-trimoxazole (CTZ)) and cell free supernatant (CFS) of a probiotic (L. plantarum) against S. Typhimurium NCTC 74. This antimicrobial combination was selected on the basis of antibiotic susceptibility pattern of Salmonella and L. plantarum.

Methods

The synergy was evaluated in terms of size of zone of inhibition, fractional inhibitory concentration index, time-kill assay (in-vitro) as well as macrophage functions (ex-vivo).

Results

The concentration producing the same or higher antibacterial effect (size of zone of inhibition) was reduced to half when both the agents were used in combination with respect to the concentrations required when used separately. CTZ and CFS exhibited synergetic activity against Salmonella by checkerboard microtitre test and the time-kill test. Ex-vivo studies demonstrated a significantly higher intracellular killing of bacteria by macrophages treated with CFS (80 AU/ml) + (CTZ) (2 μg/ml) as compared to when treated with both separately at higher concentrations. Significant reduction in the extent of lipid peroxidation and nitrite levels generated by macrophages in presence of CFS and CTZ, in conjunction, further substantiated the synergistic efficacy of the combination.

Conclusions

The antimicrobial efficacy of this combination indicates that it may serve as the basis in developing alternative strategies to combat Salmonella infections.

Down-regulation of NF-κB signalling by polyphenolic compounds prevents endotoxin-induced liver injury in a rat model

Activation of NF-κB has been reported to play a key role in causing endotoxin-induced hepatic damage through enhanced production of reactive oxygen species and pro-inflammatory mediators. In this context, the potential of polyphenolic phytochemicals in preventing endotoxin-induced liver damage remains unclear. Here, we demonstrate that catechin and quercetin have the potential to down-regulate the initial signalling molecule NF-κB which may further inhibit the downstream cascade including TNF-α and NO. These results were confirmed using N-nitro-L-arginine methyl ester (L-NAME), the inhibitor of inducible nitric oxide synthase (iNOS) along with the biochemical and histological alterations occurring in the presence and absence of supplementation with both the polyphenols. However, catechin was found to be more effective than quercetin against endotoxin-induced liver injury. These findings suggest that these polyphenols may form a pharmacological basis for designing a therapeutic agent against endotoxin-mediated oxidative damage.

Salmonella-macrophage interactions upon manganese supplementation

Various studies indicate the role of manganese (Mn) in the virulence of pathogens. Salmonella is an intracellular pathogen which is able to multiply within the macrophages. The present study was therefore, designed to assess the effect of Mn supplementation on Salmonella-macrophage interactions particularly in reference to Salmonella virulence and macrophage functions. A 50-fold decrease in the lethal dose 50 (LD(50)) of Salmonella typhimurium was observed when mice were infected with Salmonella grown in the presence of Mn as compared to the LD(50) in the absence of Mn indicating an increase in the virulence of the organism. A significant increase was observed in the levels of superoxide dismutase (SOD) of S. typhimurium grown in presence of manganese. Upon Mn supplementation, macrophage functions were also found to be altered. Decreased phagocytic activity of macrophages interacted with Salmonella was observed in presence of Mn as compared to the activity in the absence of Mn. A significant increase was observed in the extent of lipid peroxidation along with significant decreases in the activities of SOD and catalase as well as nitrite levels of macrophages interacted with S. typhimurium upon supplementation with Mn. These observations indicate that Mn supplementation might have increased the expression of Mn transporters in Salmonella resulting in increased levels of its superoxide dismutase. The altered Salmonella function in turn might have been responsible for inhibiting phagocytosis and impairing the balance between the oxidant and antioxidant profile of macrophages, thus protecting itself by exhibiting exalted virulence.

Protective efficacy of probiotic alone or in conjunction with a prebiotic in Salmonella-induced liver damage

In view of the increasing interest in the bioecological and nutritional control of diseases, use of probiotics alone or in combination with prebiotics (synbiotics) appears as a therapeutic option for various diseases. In this study, an attempt was made to explore the protective potential of Lactobacillus acidophilus as a probiotic, inulin as a prebiotic and both L. acidophilus and inulin as synbiotic against Salmonella-induced liver damage in a murine model. The probiotic, prebiotic and synbiotic supplementation resulted in decreased bacterial translocation in the liver of mice challenged with Salmonella typhimurium and decreased levels of serum aminotransferases, suggesting their protective role against Salmonella infection. Mice supplemented with these preparations before Salmonella challenge also revealed decreased levels of lipid peroxidation, increased levels of superoxide dismutase and glutathione, along with reduced levels of nitric oxide. Thus, bacteriological and biochemical alterations correlated well with the histological evidence. Protection afforded by supplementation with the probiotic alone was found to be more effective. None of the observations was suggestive of the synergistic effect in the synbiotic-supplemented animals. Thus, it is indicated that the probiotic and the prebiotic used in the present study may act by different mechanisms involved in affording protection against Salmonella-induced liver damage.

Reactive nitrogen intermediates and monokines induce caspase-3 mediated macrophage apoptosis by anaerobically stressed Salmonella typhi

A successful pathogen manipulates its host for its own benefit. After ingestion, on reaching the intestine Salmonella encounters the resident tissue macrophages. Rather than being destroyed by these professional phagocytes after internalization, Salmonella survives intracellularly. Invasive Salmonella has been reported to induce apoptosis of macrophages as a part of its infection process, which may allow it to avoid detection by the innate immune system. However, the induction of apoptosis under different host environments, including the anaerobic stress encountered by the pathogen in the gut, remains to be examined. The present study is aimed at investigating the apoptotic potential of S. enterica serovar Typhi (S. typhi) grown under anaerobic conditions simulating the in vivo situation encountered by the pathogen. Apoptotic cell death was determined by assessment of nucleosomal DNA and flow cytometric analysis. Evaluation of the data revealed that anaerobically grown S. typhi could induce apoptosis in significantly more number of macrophages compared to the bacterial cells grown under aerobic conditions. A significantly enhanced generation of reactive nitrogen intermediates and caspase-3 activity during macrophage apoptosis induced by anaerobic S. typhi correlated with the increased generation of tumour necrosis factor-alpha, interleukin (IL)-1alpha and IL-6. The results indicate that reactive nitrogen intermediates and monokines induce caspase-3 mediated apoptosis of macrophages by S. typhi under anaerobic conditions. These findings may be relevant for clearer understanding of the Salmonella-macrophage interactions and may be of clinical importance in the development of preventive intervention against the infection.

Involvement of caspase-3, lipid peroxidation and TNF-alpha in causing apoptosis of macrophages by coordinately expressed Salmonella phenotype under stress conditions

Invasive Salmonella has been reported to induce apoptosis of macrophages as a part of its infection process, which may allow it to avoid detection by the innate immune system. However, the bacterial components capable of inducing apoptosis, particularly under the environments offered by the host have not been fully identified. Therefore, in the present study, attempts were made to evaluate the apoptotic potential of Salmonella enterica serovar Typhi (S. typhi) outer membrane protein expressed under stress conditions like iron, oxidative and anaerobic simulating the in vivo situations encountered by the pathogen. Analysis of data revealed that a coordinately expressed 69kDa outer membrane protein (OMP) expressed with enhanced intensity under iron, oxidative and anaerobic stress conditions caused apoptotic cell death in 51% of macrophages, whereas OMPs of S. typhi extracted under normal conditions accounted for apoptotic cell death in only 31% of macrophages. A significantly enhanced activity of caspase-3 was observed during macrophage-apoptosis induced by this protein. A significant increase in the extent of lipid peroxidation (levels of oxidant) and decrease in the activities of antioxidants was also observed which correlated with the increased generation of tumor necrosis factor-alpha, interleukine-1alpha and interleukine-6. These results suggest that caspase-3 and tumor necrosis factor-alpha in conjunction with other cytokines may induce apoptotic cell death through the up-regulation of oxidants and down-regulation of antioxidants. These findings may be relevant for the better understanding of the disease pathophysiology and for the future developments of diagnostic and preventive strategies during the host-pathogen interactions.