Induction of Salmonella stress proteins upon infection of macrophages

Salmonella Typhimurium employs spermidine to exert protection against ROS-mediated cytotoxicity and rewires host polyamine metabolism to ameliorate its survival in macrophages

Salmonella infection entails a cascade of attacks and defence measures. After breaching the intestinal epithelial barrier, Salmonella is phagocytosed by macrophages, where the bacteria encounter multiple stresses, to which it employs relevant countermeasures. Our study shows that, in Salmonella, the polyamine spermidine activates a stress response mechanism by regulating critical antioxidant genes. Salmonella Typhimurium mutants for spermidine transport and synthesis cannot mount an antioxidative response, resulting in high intracellular ROS levels. These mutants are also compromised in their ability to be phagocytosed by macrophages. Furthermore, it regulates a novel enzyme in Salmonella, Glutathionyl-spermidine synthetase (GspSA), which prevents the oxidation of proteins in E. coli. Moreover, the spermidine mutants and the GspSA mutant show significantly reduced survival in the presence of hydrogen peroxide in vitro and reduced organ burden in the mouse model of Salmonella infection. Conversely, in macrophages isolated from gp91phox-/- mice, we observed a rescue in the attenuated fold proliferation previously observed upon infection. We found that Salmonella upregulates polyamine biosynthesis in the host through its effectors from SPI-1 and SPI-2, which addresses the attenuated proliferation observed in spermidine transport mutants. Thus, inhibition of this pathway in the host abrogates the proliferation of Salmonella Typhimurium in macrophages. From a therapeutic perspective, inhibiting host polyamine biosynthesis using an FDA-approved chemopreventive drug, D, L-α-difluoromethylornithine (DFMO), reduces Salmonella colonisation and tissue damage in the mouse model of infection while enhancing the survival of infected mice. Therefore, our work provides a mechanistic insight into the critical role of spermidine in stress resistance of Salmonella. It also reveals a bacterial strategy in modulating host metabolism to promote their intracellular survival and shows the potential of DFMO to curb Salmonella infection.

Chaperone Hsp70 helps Salmonella survive infection-relevant stress by reducing protein synthesis

In all domains of life, Hsp70 chaperones preserve protein homeostasis by promoting protein folding and degradation and preventing protein aggregation. We now report that the Hsp70 from the bacterial pathogen Salmonella enterica serovar Typhimurium-termed DnaK-independently reduces protein synthesis in vitro and in S. Typhimurium facing cytoplasmic Mg2+ starvation, a condition encountered during infection. This reduction reflects a 3-fold increase in ribosome association with DnaK and a 30-fold decrease in ribosome association with trigger factor, the chaperone normally associated with translating ribosomes. Surprisingly, this reduction does not involve J-domain cochaperones, unlike previously known functions of DnaK. Removing the 74 C-terminal amino acids of the 638-residue long DnaK impeded DnaK association with ribosomes and reduction of protein synthesis, rendering S. Typhimurium defective in protein homeostasis during cytoplasmic Mg2+ starvation. DnaK-dependent reduction in protein synthesis is critical for survival against Mg2+ starvation because inhibiting protein synthesis in a dnaK-independent manner overcame the 10,000-fold loss in viability resulting from DnaK truncation. Our results indicate that DnaK protects bacteria from infection-relevant stresses by coordinating protein synthesis with protein folding capacity.

Understanding Staphylococcus aureus internalisation and induction of antimicrobial tolerance

INTRODUCTION

Staphylococcus aureus, a human commensal, is also one of the most common and serious pathogens for humans. In recent years, its capacity to survive and replicate in phagocytic and non-phagocytic cells has been largely demonstrated. In these intracellular niches, bacteria are shielded from the immune response and antibiotics, turning host cells into long-term infectious reservoirs. Moreover, neutrophils carry intracellular bacteria in the bloodstream, leading to systemic spreading of the disease. Despite the serious threat posed by intracellular S. aureus to human health, the molecular mechanisms behind its intracellular survival and subsequent antibiotic treatment failure remain elusive.

AREA COVERED

We give an overview of the killing mechanisms of phagocytes and of the impressive arsenal of virulence factors, toxins and stress responses deployed by S. aureus as a response. We then discuss the different barriers to antibiotic activity in this intracellular niche and finally describe innovative strategies to target intracellular persisting reservoirs.

EXPERT OPINION

Intracellular niches represent a challenge in terms of diagnostic and treatment. Further research using ad-hoc in-vivo models and single cell approaches are needed to better understand the molecular mechanisms underlying intracellular survival and tolerance to antibiotics in order to identify strategies to eliminate these persistent bacteria.

Protective effects of α-terpineol and Bacillus coagulans on intestinal function in weaned piglets infected with a recombinant Escherichia coli expressing heat-stable enterotoxin STa

This study was to investigate the impact of α-terpineol (α-TPN) and Bacillus coagulans (B. coagulans) on weaned piglets infected with Enterotoxigenic Escherichia coli (ETEC). Thirty-two weaned piglets were assigned into four treatments: Control group (basal diet), STa group (basal diet + 1 × 10¹⁰ CFU ETEC), TPN+STa group (basal diet + 0.01% α-TPN + ETEC) and BC+STa group (basal diet + 2 × 10⁶ CFU B. coagulans + ETEC). Result showed that both α-TPN and B. coagulans could alleviate diarrhea (decreased diarrhea rate), intestinal injury (improved intestinal morphology, decreased blood I-FABP concentration, increased protein expression level of Occludin), oxidative stress (increased GSH-Px activity and decreased MDA content) and inflammation (altered concentration of TNF-α, IL-1β in blood) induced by ETEC infection. Mechanism investigation further demonstrated that the beneficial effects of α-TPN and B. coagulans supplementation upon ETEC infection may be achieved by decreasing the protein expression levels of caspase-3, AQP4 and p-NF-κB and decreasing the gene expression levels of INSR and PCK1. Besides, α-TPN supplementation could specifically decreased expression level of gene b ^0,+ AT, and B. coagulans supplementation could specifically decreased expression level of gene AQP10 and protein HSP70 in ETEC-infected weaned piglets. These results suggested that α-TPN and B. coagulans can be used as antibiotic alternatives against ETEC infection in weaned piglets.

M.tb-Rv2462c of Mycobacterium tuberculosis Shows Chaperone-like Activity and Plays a Role in Stress Adaptation and Immunomodulation

Mycobacterium tuberculosis (M.tb)-encoded factors protect it against host-generated stresses and support its survival in the hostile host environment. M.tb possesses two peptidyl-prolyl cis-trans isomerases and a probable trigger factor encoded by Rv2462c which has an FKBP-like PPIase domain. PPIases are known to assist the folding of peptidyl-prolyl bonds and are involved in various cellular processes important for bacterial survival in host-generated stresses. In this study, we aim to functionally characterize Rv2462c of M.tb. Our data suggest that the trigger factor of M.tb exhibits chaperone activity both in vitro and in vivo. Heterologous expression of M.tb-Rv2462c locus into Mycobacterium smegmatis enhanced its survival within macrophages, adaptation to oxidative stress and biofilm formation. M.tb-trigger factor has strong immunomodulatory potential and modifies the cytokine profile of the host towards the proinflammatory axis.

Assessment of free radicals and reactive oxygen species milieu in nanoparticles adjuvanted outer membrane proteins vaccine against Salmonella typhi

In this study, calcium phosphate nanoparticles-based (STCNV) and montanide oil adjuvant vaccine (STOAV) containing outer membrane proteins (Omps) of S. Typhi were evaluated for inducing oxidative stress indicators [reduced glutathione (GSH), lipid peroxidation (LPO), catalase, superoxide dismutase (SOD), and total protein] in the tissues of mice after vaccination. The GSH levels though slightly high in the liver, kidney, and lungs of STCNV group were not significantly different from STOAV and the control group (STC). There was no significant difference in LPO levels in any group for any tissue. The significantly lower activities of catalase were observed in the kidney and lungs of the STCNV group as compared to STOAV and STC group, while in the liver, STCNV group revealed lower catalase activity in comparison to the control group. No significant difference in the SOD activities between the two vaccinated groups was observed. The total protein contents in all the organs showed no significant difference in the vaccinated and the control group. The vaccines may induce long-term inflammatory response and consequently damage vital organs; this study revealed no long-term oxidative stress in all the three vital organs, suggesting that these vaccines may not cause oxidative damages in the vital organs of mice.

Role of HrcA in stress management in Mycobacterium tuberculosis

AIM

The current study aims to understand the role of HrcA in stress response of M. tuberculosis.

METHODS AND RESULTS

In this study, using an hrcA knock out mutant of M. tuberculosis it is demonstrated that the heat shock repressor, HrcA is important for countering environmental stresses pathogen faces within the host during the infection process. Also, with scanning electron microscopy it has been shown that HrcA plays a role in maintaining the morphology and cell size of the pathogen as disruption of the hrcA gene resulted in significantly elongated bacilli. Further, heat shock proteins like ClpC1, ClpB, DnaK, GroEL2, GroEL1, DnaJ2 and GroES were detected in the secretome of M. tuberculosis by mass spectrometric analysis. The study also demonstrates a strong humoral response against M. tuberculosis heat shock proteins in H₃₇ R_v infected mice sera.

CONCLUSION

The study establishes that though hrcA is not an essential gene for M. tuberculosis, it regulates the expression of heat shock proteins during infection, and disruption of hrcA gives a survival advantage to the pathogen during stress conditions.

SIGNIFICANCE

and Impact of the Study: HrcA plays an important role in maintaining a fine balance of heat shock proteins during infection to give adequate survival advantage and also evade immune detection.

Deletion of both methionine sulfoxide reductase A and methionine sulfoxide reductase C genes renders Salmonella Typhimurium highly susceptible to hypochlorite stress and poultry macrophages

Salmonella Typhimurium survives and replicates inside the oxidative environment of phagocytic cells. Proteins, because of their composition and location, are the foremost targets of host inflammatory response. Among others, Met-residues are highly prone to oxidation. Methionine sulfoxide reductase (Msr), with the help of thioredoxin-thioredoxin reductase, can repair oxidized methionine (Met-SO) residues to Met. There are four methionine sulfoxide reductases localized in the cytosol of S. Typhimurium, MsrA, MsrB, MsrC and BisC. MsrA repairs both protein-bound and free 'S' Met-SO, MsrB repairs protein-bound 'R' Met-SO, MsrC repairs free 'R' Met-SO and BisC repairs free 'S' Met-SO. To assess the role(s) of various Msrs in Salmonella, few studies have been conducted by utilizing ΔmsrA, ΔmsrB, ΔmsrC, ΔmsrAΔmsrB, ΔmsrBΔmsrC and ΔbisC mutant strains of S. Typhimurium. Out of the above-mentioned mutants, ΔmsrA and ΔmsrC were found to play important role in the stress survival of this bacterium; however, the combined roles of these two genes have not been determined. In the current study, we have generated msrAmsrC double gene deletion strain (ΔmsrAΔmsrC) of S. Typhimurium and evaluated the effect of gene deletions on the survival of Salmonella against hypochlorite stress and intramacrophage replication. In in vitro growth curve analysis, ΔmsrAΔmsrC mutant strain showed a longer lag phase during the initial stages of the growth; however, it attained similar growth as the wild type strain of S. Typhimurium after 5 h. The ΔmsrAΔmsrC mutant strain has been highly (~ 3000 folds more) sensitive (p < 0.001) to hypochlorite stress. Further, ΔmsrA and ΔmsrAΔmsrC mutant strains showed more than 8 and 26 folds more susceptibility to poultry macrophages, respectively. Our data suggest that the deletion of both msrA and msrC genes severely affect the oxidative stress survival and intramacrophage proliferation of S. Typhimurium.

Perinatal Infection: A Major Contributor to Efficacy of Cooling in Newborns Following Birth Asphyxia

Neonatal encephalopathy (NE) is a global burden, as more than 90% of NE occurs in low- and middle-income countries (LMICs). Perinatal infection seems to limit the neuroprotective efficacy of therapeutic hypothermia. Efforts made to use therapeutic hypothermia in LMICs treating NE has led to increased neonatal mortality rates. The heat shock and cold shock protein responses are essential for survival against a wide range of stressors during which organisms raise their core body temperature and temporarily subject themselves to thermal and cold stress in the face of infection. The characteristic increase and decrease in core body temperature activates and utilizes elements of the heat shock and cold shock response pathways to modify cytokine and chemokine gene expression, cellular signaling, and immune cell mobilization to sites of inflammation, infection, and injury. Hypothermia stimulates microglia to secret cold-inducible RNA-binding protein (CIRP), which triggers NF-κB, controlling multiple inflammatory pathways, including nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasomes and cyclooxygenase-2 (COX-2) signaling. Brain responses through changes in heat shock protein and cold shock protein transcription and gene-expression following fever range and hyperthermia may be new promising potential therapeutic targets.

Attenuated Salmonella enterica Serovar Typhimurium, Strain NC983, Is Immunogenic, and Protective against Virulent Typhimurium Challenges in Mice

Non-typhoidal Salmonella (NTS) serovars are significant health burden worldwide. Although much effort has been devoted to developing typhoid-based vaccines for humans, currently there is no NTS vaccine available. Presented here is the efficacy of a live attenuated serovar Typhimurium strain (NC983). Oral delivery of strain NC983 was capable of fully protecting C57BL/6 and BALB/c mice against challenge with virulent Typhimurium. Strain NC983 was found to elicit an anti-Typhimurium IgG response following administration of vaccine and boosting doses. Furthermore, in competition experiments with virulent S. Typhimurium (ATCC 14028), NC983 was highly defective in colonization of the murine liver and spleen. Collectively, these results indicate that strain NC983 is a potential live attenuated vaccine strain that warrants further development.

YshB Promotes Intracellular Replication and Is Required for Salmonella Virulence

Salmonella virulence requires the initial invasion of host cells, followed by modulation of the intracellular environment for survival and replication. In an effort to characterize the role of small RNAs in Salmonella pathogenesis, we inadvertently identified a 5-kDa protein named YshB that is involved in the intracellular survival of Salmonella We show here that yshB expression is upregulated upon entry into macrophages. When yshB expression is upregulated before bacterial entry, invasion efficiency is inhibited. Lack of YshB resulted in reduced bacterial survival within the macrophages and led to reduced virulence in a mouse model of infection.IMPORTANCE Salmonella gastroenteritis is one of the most common causes of foodborne disease, possibly affecting millions of people globally each year. Here we characterize the role of a novel small protein, YshB, in mediating Salmonella intracellular survival. This elucidation adds to the body of knowledge regarding how this bacterium achieves intracellular survival.

Interplay of oxidative stress and antioxidant bio markers in oil adjuvant Brucella melitensis vaccinated and challenged mice

The intracellular nature of Brucella leads to rise in oxidative stress due to bacterial invasion, particularly at the site of predilection spleen and lymph nodes. The present study aimed to evaluate the erythrocytic and tissue specific oxidative stress responses induced during oil adjuvant killed Brucella melitensis vaccination. The results of the study clearly implicated a significant increase in level of catalase, and superoxide dismutase (SOD) activity and lipid peroxidation (LPO), and total protein content in erythrocytes after vaccination. The activity of glutathione-S-transferase (GST) was unaltered during the period of experiment. The catalase activity and GSH content was significantly increased in lung and spleen tissues. The tissues GST levels increased significantly in all tissues, while tissue SOD level increased significantly only in lung tissues. Thus, it can be inferred that oil adjuvant based Brucella vaccine induces negligible signs of inflammatory pathophysiology and supports the development of significant level of protection against virulent Brucella challenge.

Pharmacologic ascorbate as a pro-drug for hydrogen peroxide release to kill mycobacteria

BACKGROUND AND PURPOSE

Tuberculosis is one of the most highly fatal diseases worldwide, and one-third of the world's population has been infected with Mycobacterium tuberculosis (M. tuberculosis). A previous study showed that M. tuberculosis was highly susceptible to being killed by ascorbate (i.e. vitamin C, VC), but the molecular mechanisms of the bactericidal activity of VC against M. tuberculosis are still not well understood.

EXPERIMENTAL APPROACH

We assayed the effects of VC as an anti-tuberculosis drug against mycobacteria (i.e. M. bovis BCG or M. tuberculosis H37Rv) in macrophages (i.e. RAW 264.7 cells). Relative global protein expression changes in 5 mM VC-treated and control samples of H37Rv were investigated by Tandem mass tag (TMT)-based quantitative proteomic analysis. qRT-PCR was also used to measure the differential expression of six intracellular stress response mycobacteria genes.

KEY RESULTS

Quantitative proteomic analysis showed that 11 peptide components including rip3, fdxA, Rv2028c, mtp, LH57_00670, hspX, pfkB, Rv1824, Rv1813c, LH57_08410 and Rv2030c were up-regulated and 17 peptide components were down-regulated in 5 mM VC-treated H37Rv compared with the control samples. qRT-PCR also verified that VC could induce the expression of six genes (hsp, fdxD, furA, devR, hspX, and dnaB) in BCG and H37Rv. We also found that exosomes from RAW 264.7 cells treated with pharmacologic VC could kill M. bovis BCG in vitro.

CONCLUSION AND IMPLICATIONS

Our results demonstrated that the bactericidal activity of VC against mycobacteria, as a pro-drug for hydrogen peroxide formation (H2O2), was dependent on reactive oxygen species production and the activated oxidative stress pathway, which suggested that pharmaceutical VC and exosomes from macrophages treated with VC could be used as potential anti-tuberculosis drugs.

Quantifying changes in the bacterial thiol redox proteome during host-pathogen interaction

Phagocyte-derived production of a complex mixture of different oxidants is a major mechanism of the host defense against microbial intruders. On the protein level, a major target of these oxidants is the thiol group of the amino acid cysteine in proteins. Oxidation of thiol groups is a widespread regulatory post-translational protein modification. It is used by bacteria to respond to and to overcome oxidative stress. Numerous redox proteomic studies have shown that protein thiols in bacteria, such as Escherichia coli react towards a number of oxidants in specific ways. However, our knowledge about protein thiols in bacteria exposed to the complex mixture of oxidants encountered in the phagolysosome is still limited. In this study, we used a quantitative redox proteomic method (OxICAT) to assess the in vivo thiol oxidation status of phagocytized E. coli. The majority (65.5%) of identified proteins harbored thiols that were significantly oxidized (> 30%) upon phagocytosis. A substantial number of these proteins are from major metabolic pathways or are involved in cell detoxification and stress response, suggesting a systemic breakdown of the bacterial cysteine proteome in phagocytized bacteria. 16 of the oxidized proteins provide E. coli with a significant growth advantage in the presence of H₂O₂, when compared to deletion mutants lacking these proteins, and 11 were shown to be essential under these conditions.

Comparative Genomic Studies of Salmonella Heidelberg Isolated From Chicken- and Turkey-Associated Farm Environmental Samples

Salmonella is one of the leading causes of human foodborne gastroenteritis in the United States. In addition, Salmonella contributes to morbidity and mortality in livestock. The control of Salmonella is an increasing problematic issue in livestock production due to lack of effective control methods and the constant adaptation of Salmonella to new management practices, which is often related to horizontal acquisition of virulence or antibiotic resistance genes. Salmonella enterica serotype Heidelberg is one of the most commonly isolated serotypes in all poultry production systems in North America. Emergence and persistence of multi-drug resistant Salmonella Heidelberg isolates further impact the poultry production and public health. We hypothesized that distinct poultry production environments affect Salmonella genomic content, and by consequence its survival and virulence abilities. This study compared the genomic composition of S. Heidelberg isolated from environmental samples (19 chicken and 12 turkey isolates) of different breeder farms (16 chicken and 8 turkey farms) in the Midwest, United States. Whole genome comparison of 31 genomes using RAST and SEED identified differences in specific sub-systems in isolates between the chicken- and turkey-associated farm environmental samples. Genes associated with the type IV secretion system (n = 12) and conjugative transfer (n = 3) were absent in turkey farm isolates compared to the chicken ones (p-value < 0.01); Further, turkey farm isolates were enriched in prophage proteins (n = 53; p-value < 0.01). Complementary studies using PHASTER showed that prophages were all Caudovirales phages and were more represented in turkey environmental isolates than the chicken isolates. This study corroborates that isolates from distinct farm environment show differences in S. Heidelberg genome content related to horizontal transfer between bacteria or through viral infections. Complementary microbiome studies of these samples would provide critical insights on sources of these variations. Overall, our findings enhance the understanding of Salmonella genome plasticity and may aid in the development of future effective management practices to control Salmonella.

Beneficial Impact and Molecular Mechanism of Bacillus coagulans on Piglets' Intestine

The aim of this research was to investigate the beneficial impact and molecular mechanism of B. coagulans on piglets' intestine. Twenty-four 21 days old weaned piglets were allotted to three treatments: Control group (basal diet), B6 group (basal diet + 2 × 10⁶ CFU/g B. coagulans), and the B7 group (basal diet + 2 × 10⁷ CFU/g B. coagulans). The results showed that, compared with the control group, the B7 group had a reduced cholesterol content and gamma glutamyl transpeptidase (GGT) in plasma (p < 0.05); the B6 and B7 groups had a significantly decreased diarrhea rate and diamine oxidase (DAO) activity in plasma (p < 0.05), increased villus height in ileum and decreased crypt depth in the jejunum (p < 0.05); increased activities of superoxide dismutase (SOD) and catalase (CAT), and decreased the content of malondialdehyde (MDA) and H₂O₂ in the intestine (p < 0.05). These data suggested that supplementing B. coagulans had beneficial impacts on promoting nutrients' metabolism, maintaining intestinal integrity, and alleviating oxidative stress and diarrhea. Further research of molecular mechanisms showed changing expression levels of related proteins and genes, suggesting that these could be involved in the regulation of the impact. The community composition of the gut microbiota was also found to be altered in several operational taxonomic units within the genus, Prevotella (order Bacteroidales), and the order, Clostridiales.

Integrated proteomics, genomics, metabolomics approaches reveal oxalic acid as pathogenicity factor in Tilletia indica inciting Karnal bunt disease of wheat

Tilletia indica incites Karnal bunt (KB) disease in wheat. To date, no KB resistant wheat cultivar could be developed due to non-availability of potential biomarkers related to pathogenicity/virulence for screening of resistant wheat genotypes. The present study was carried out to compare the proteomes of T. indica highly (TiK) and low (TiP) virulent isolates. Twenty one protein spots consistently observed as up-regulated/differential in the TiK proteome were selected for identification by MALDI-TOF/TOF. Identified sequences showed homology with fungal proteins playing essential role in plant infection and pathogen survival, including stress response, adhesion, fungal penetration, invasion, colonization, degradation of host cell wall, signal transduction pathway. These results were integrated with T. indica genome sequence for identification of homologs of candidate pathogenicity/virulence related proteins. Protein identified in TiK isolate as malate dehydrogenase that converts malate to oxaloacetate which is precursor of oxalic acid. Oxalic acid is key pathogenicity factor in phytopathogenic fungi. These results were validated by GC-MS based metabolic profiling of T. indica isolates indicating that oxalic acid was exclusively identified in TiK isolate. Thus, integrated omics approaches leads to identification of pathogenicity/virulence factor(s) that would provide insights into pathogenic mechanisms of fungi and aid in devising effective disease management strategies.

Fever as an important resource for infectious diseases research

Fever or pyrexia is a process where normal body temperature is raised over homeostasis conditions. Although many effects of fever over the immune system have been known for a long time, it has not been until recent studies when these effects have been evaluated in several infection processes. Results have been promising, as they have reported new ways of regulation, especially in RNA molecules. In light of these new studies, it seems important to start to evaluate the effects of pyrexia in current research efforts in host-pathogen interactions. Viruses and bacteria are responsible for different types of infectious diseases, and while it is of paramount importance to understand the mechanisms of infection, potential effects of fever on this process may have been overlooked. This is especially relevant because during the course of many infectious diseases the organism develops fever. Due to the lack of specific treatments for many of those afflictions, experimental evaluation in fever-like conditions can potentially bring new insights into the infection process and can ultimately help to develop treatments. The aim of this review is to present evidence that the temperature increase during fever affects the way the infection takes place, for both the pathogen and the host.

Missing the target: DNAk is a dominant epitope in the humoral immune response of channel catfish (Ictalurus punctatus) to Flavobacterium columnare

Vaccination remains a viable alternative for bacterial disease protection in fish; however additional work is required to understand the mechanisms of adaptive immunity in the channel catfish. To assess the humoral immune response to Flavobacterium columnare; a group of channel catfish were first immunized with F. columnare LV-359-01 cultured in iron-depleted media, before being challenged with wild type F. columnare LV-359-01. The immunization protocol did not confer increased protection against F. columnare; however both control and immunized responders generated serum and skin IgM antibodies against F. columnare proteins. Western blot analyses of individuals from both groups showed that IgM antibodies were generated to the same 70 kDa extracellular protein, which was identified to be the bacterial chaperonin protein DNAk. Antibodies generated were cross reactive to DNAk proteins found in other gram negative bacteria. Our data suggests that DNAk is the dominant epitope in the channel catfish B-cell response to F. columnare.

Protein homeostasis-more than resisting a hot bath

Maintenance of protein homeostasis is essential for survival of all organisms. In bacteria, the protein quality control system has a broad physiological impact beyond heat shock resistance, being involved in virulence, antibiotic resistance, as well as protection against environmental stresses. Its contribution to rejuvenation and growth arrest suggests interference with protein quality control to be a novel antimicrobial strategy. Remarkably, a protein quality control module originating from environmental strains has been found to be horizontally transferred to predominant clonal groups of bacteria providing exquisite thermotolerance to recently emerged global pathogens suggesting that novel features related to protein homeostasis contribute to the transition to new environments.

Identification of the immunogenic spore and vegetative proteins of Bacillus anthracis vaccine strain A16R

Immunoproteomics was used to screen the immunogenic spore and vegetative proteins of Bacillus anthracis vaccine strain A16R. The spore and vegetative proteins were separated by 2D gel electrophoresis and transferred to polyvinylidene difluoride membranes, and then western blotting was performed with rabbit immune serum against B.anthracis live spores. Immunogenic spots were cut and digested by trypsin. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed to identify the proteins. As a result, 11 and 45 immunogenic proteins were identified in the spores and vegetative cells, respectively; 26 of which have not been reported previously. To verify their immunogenicity, 12 of the identified proteins were selected to be expressed, and the immune sera from the mice vaccinated by the 12 expressed proteins, except BA0887, had a specific western blot band with the A16R whole cellular lytic proteins. Some of these immunogenic proteins might be used as novel vaccine candidates themselves or for enhancing the protective efficacy of a protective-antigen-based vaccine.

Vita-PAMPs: signatures of microbial viability

Can the innate immune system detect and respond to microbial viability? Using bacteria as a model, we found that indeed the very essence of microbial infectivity, viability itself, can be detected, and notably, in the absence of the activity of virulence factors. The microbial molecule that serves as the signature of viability is bacterial messenger RNA (mRNA), common to all bacteria, and without which bacteria cannot survive. Prokaryotic mRNAs also differ from eukaryotic mRNAs in several ways, and as such, these features all fulfill the criteria, and more, for a pathogen-associated molecular pattern (PAMP) as originally proposed by Charles Janeway. Because these mRNAs are lost from dead bacteria, they belong to a special class of PAMPs, which we call vita-PAMPs. Here we discuss the possible receptors and pathways involved in the detection of bacterial mRNAs, and thus microbial viability. We also consider examples of vita-PAMPs other than bacterial mRNA.

Blood heat shock proteins evoked by some Salmonella strains infection in ducks

Bacterial heat-shock response is a global regulatory system required for effective adaptation to changes (stress) in the environment. An in vitro study was conducted to investigate the impact of a sublethal temperature (42°C) on heat shock protein (HSP) expression in 6 Salmonella strains (Salmonella Enteritidis, S. Typhimurium, S. Virchow, S. Shubra, S. Haifa and S. Eingedi). The 6 Salmonella strains were isolated from the tissues of ducklings that had died from avian salmonellosis. To determine the induction of HSP in the 6 Salmonella strains, they were exposed to the selected temperature level for 24 h and further kept for 48 h at culturing condition of 42°C. Growth under a sublethal temperature of 42°C increased the expression of several proteins of Salmonella, including a 63 kDa protein in addition to the generation and/or overexpression of 143 proteins which were specific to heat shock, concurrent to this acquired thermotolerance. The 6 Salmonella strains responded to 24 h of thermal stress at an elevated temperature 42°C by synthesizing different heat shock proteins (HSP) with molecular weights ranging between 13.62 and 96.61 kDa. At 48 h, the 6 Salmonella strains synthesized different HSPs with molecular weights ranging between 14.53 and 103.43 kDa. It follows that salmonellae would produce HSPs during the course of the infectious process. Salmonellosis produced several proteins after 24 and 48 h of infection. Seven of these proteins (100, 80, 60, 40, 30, 20 and 10 kDa) were recognized in the serum obtained from the ducklings infected with S. Enteritidis, S. Typhimurium, S. Virchow, S. Shubra, S. Haifa and S. Eingedi after 24 h of infection. After 48 h, the 1-7 kDa HSP became more evident and indicated their de novo generation.

ThehtpABoperon ofLegionella pneumophilacannot be deleted in the presence of thegroEchaperonin operon ofEscherichia coli

HtpB, the chaperonin of the intracellular bacterial pathogen Legionella pneumophila , displays several virulence-related functions in vitro. To confirm HtpB’s role in vivo, host infections with an htpB deletion mutant would be required. However, we previously reported that the htpAB operon (encoding co-chaperonin and chaperonin) is essential. We attempted here to delete htpAB in a L. pneumophila strain carrying the groE operon (encoding the Escherichia coli co-chaperonin and chaperonin). The groE operon was inserted into the chromosome of L. pneumophila Lp02, and then allelic replacement of htpAB with a gentamicin resistance cassette was attempted. Although numerous potential postallelic replacement transformants showed a correct selection phenotype, we still detected htpAB by PCR and full-size HtpB by immunoblot. Southern blot and PCR analysis indicated that the gentamicin resistance cassette had apparently integrated in a duplicated htpAB region. However, we showed by Southern blot that strain Lp02, and the Lp02 derivative carrying the groE operon, have only one copy of htpAB. These results confirmed that the htpAB operon cannot be deleted, not even in the presence of the groE operon, and suggested that attempts to delete htpAB under strong phenotypic selection result in aberrant genetic recombinations that could involve duplication of the htpAB locus.

Detection of prokaryotic mRNA signifies microbial viability and promotes immunity

Live vaccines have long been known to trigger far more vigorous immune responses than their killed counterparts. This has been attributed to the ability of live microorganisms to replicate and express specialized virulence factors that facilitate invasion and infection of their hosts. However, protective immunization can often be achieved with a single injection of live, but not dead, attenuated microorganisms stripped of their virulence factors. Pathogen-associated molecular patterns (PAMPs), which are detected by the immune system, are present in both live and killed vaccines, indicating that certain poorly characterized aspects of live microorganisms, not incorporated in dead vaccines, are particularly effective at inducing protective immunity. Here we show that the mammalian innate immune system can directly sense microbial viability through detection of a special class of viability-associated PAMPs (vita-PAMPs). We identify prokaryotic messenger RNA as a vita-PAMP present only in viable bacteria, the recognition of which elicits a unique innate response and a robust adaptive antibody response. Notably, the innate response evoked by viability and prokaryotic mRNA was thus far considered to be reserved for pathogenic bacteria, but we show that even non-pathogenic bacteria in sterile tissues can trigger similar responses, provided that they are alive. Thus, the immune system actively gauges the infectious risk by searching PAMPs for signatures of microbial life and thus infectivity. Detection of vita-PAMPs triggers a state of alert not warranted for dead bacteria. Vaccine formulations that incorporate vita-PAMPs could thus combine the superior protection of live vaccines with the safety of dead vaccines.

The analysis of groEL gene in Salmonella enterica subspecies enterica serovar Typhimurium isolated from avians by PCR-Restriction Fragment Length Polymorphism method

Salmonella enterica subspecies enterica serovar Typhimurium causes food-borne outbreaks and systemic diseases in humans and animals. groEL gene (also known as mopA gene in S. Typhimurium), possessing conserved sequence, plays an important role in invasion of bacteria. The purpose of present study was to identify the polymorphism of groEL gene among different avians in different regions by PCR-RFLP method. Fifty two S. Typhimurium isolates (Broiler (n = 13), Layer (n = 12), Duck (n = 5), Goose (n = 5), Sparrow (n = 8), Canary (n = 3), Pigeon (n = 5) and Casco parrot (n = 1). were identified using serotyping as well as multiplex-PCR. Then, amplification of groEL gene performed and amplified products subjected to restriction digestion with BsuRI enzyme. Three RFLP profiles, A, B and C, generated DNA fragments between approximately 100-1,000 bp in size, were observed. The RFLP profile A was observed in 35 (67.3%), profile B in 14 (26.9%) and profile C in 3 (5.77%) of isolates. S. Typhimurium isolates recovered from 13 broilers (two of which profile A, 9 profile B and 2 profile C) and from 8 sparrows (two of which profile A, 5 profile B and 1 profile C) showed all three profiles, but 12 layers and other avians (including Canary (n = 3), Goose (n = 5), Duck (n = 5), Pigeon (n = 5) and Casco parrot (n = 1)) showed profile A. None of these profiles was allotted for a special region. The result of present study showed that S. Typhimurium undergoes genetic mutations in groEL gene under unpleasant milieu in different regions and in different avians. Thus, genetic diversity, despite conserved nature of groEL gene in S. Typhimurium, may exist but it depends on the condition where bacteria have settled. To our knowledge, three RFLP profiles of groEL gene generated by BsuRI restriction enzyme were not reported previously.

Role of heat shock proteins in diseases and their therapeutic potential

Heat shock proteins are ubiquitously expressed intracellular proteins and act as molecular chaperones in processes like protein folding and protein trafficking between different intracellular compartments. They are induced during stress conditions like oxidative stress, nutritional deficiencies and radiation. They are released into extracellular compartment during necrosis. However, recent research findings highlights that, they are not solely present in cytoplasm, but also released into extracellular compartment during normal conditions and even in the absence of necrosis. When present in extracellular compartment, they have been shown to perform various functions like antigen presentation, intercellular signaling and induction of pro-inflammatory cytokines. Heat shock proteins represents as dominant microbial antigens during infection. The phylogenetic similarity between prokaryotic and eukaryotic heat shock proteins has led to proposition that, microbial heat shock proteins can induce self reactivity to host heat shock proteins and result in autoimmune diseases. The self-reactivity of heat shock proteins protects host against disease by controlling induction and release of pro-inflammatory cytokines. However, antibodies to self heat shock proteins haven been implicated in pathogenesis of autoimmune diseases like arthritis and atherosclerosis. Some heat shock proteins are potent inducers of innate and adaptive immunity. They activate dendritic cells and natural killer cells through toll-like receptors, CD14 and CD91. They play an important role in MHC-antigen processing and presentation. These immune effector functions of heat shock proteins are being exploited them as therapeutic agents as well as therapeutic targets for various infectious diseases and cancers.

Diversity of multidrug-resistant salmonella enterica strains associated with cattle at harvest in the United States

The prevalence and diversity of multidrug-resistant (MDR) Salmonella enterica strains associated with cattle at harvest in the United States were examined. Hides and carcasses of cattle were sampled at processing plants (n = 6) located in four geographically distant regions from July 2005 to April 2006. The mean prevalences of Salmonella on hides, preevisceration carcasses (immediately after hide removal), and postintervention carcasses (in the chiller and after the full complement of interventions) were 89.6%, 50.2%, and 0.8%, respectively. The values for MDR Salmonella enterica strains (defined as those resistant to two or more antimicrobials) as percentages of Salmonella prevalence were 16.7% (95% confidence interval [CI], 8.3 to 25.1%; median percent prevalence, 6.9%), 11.7% (95% CI, 4.4 to 19.0%; median, 4.8%), and 0.33% (95% CI, -0.3 to 0.70%; median, 0%), respectively. In this study, 16,218 Salmonella hide and carcass isolates were screened for antimicrobial resistance. Of these, 978 (6.0%) unique MDR S. enterica isolates were identified and serotyped and their XbaI pulsed-field gel electrophoresis (PFGE) profiles determined. The predominant MDR S. enterica serotypes observed were Newport (53.1%), Typhimurium (16.6%), and Uganda (10.9%). Differences in MDR S. enterica prevalence were detected, and PFGE analysis revealed both epidemic clusters (profiles found in plants in multiple regions/seasons) and endemic clusters (profiles observed in plants in limited regions/seasons) within several of the MDR serotypes examined. Despite these differences, multiple-hurdle processing interventions employed at all plants were found to be quite effective and decreased Salmonella carcass contamination by 98.4% (95% CI, 97.6 to 99.7%).

Microarray analysis of response of Salmonella during infection of HLA-B27- transfected human macrophage-like U937 cells

BACKGROUND

Human leukocyte antigen (HLA)-B27 is strongly associated with the development of reactive arthritis (ReA) in humans after salmonellosis. Human monocytic U937 cells transfected with HLA-B27 are less able to eliminate intracellular Salmonella enterica serovar Enteritidis than those transfected with control HLA antigens (e.g. HLA-A2). To investigate further the mechanisms by which HLA-B27-transfected cells allow increased replication of these bacteria, a DNA-based microarray was used for comparative genomic analysis of S. Enteritidis grown in HLA-B27- or HLA-A2-transfected cells. The microarray consisted of 5080 oligonucleotides from different serovars of Salmonella including S. Enteritidis PT4-specific genes. Bacterial RNA was isolated from the infected HLA-B27- or HLA-A2-transfected cells, reverse-transcribed to cDNA, and hybridized with the oligonucleotides on the microarrays. Some microarray results were confirmed by RT-PCR.

RESULTS

When gene expression was compared between Salmonella grown in HLA-B27 cells and in HLA-A2 cells, 118 of the 4610 S. Enteritidis-related genes differed in expression at 8 h after infection, but no significant difference was detectable at 2 h after infection. These differentially expressed genes are mainly involved in Salmonella virulence, DNA replication, energy conversion and metabolism, and uptake and metabolism of nutrient substances, etc. The difference suggests HLA-B27-dependent modulation of Salmonella gene expression, resulting in increased Salmonella replication in HLA-B27-positive cells. Among the up-regulated genes were those located in Salmonella pathogenicity island (SPI)-2, which play a central role in intracellular survival and replication of Salmonella.

CONCLUSIONS

This is the first report to show the regulation of Salmonella gene expression by HLA-B27 during infection of host cells. This regulation probably leads to increased Salmonella survival and replication in HLA-B27-positive cells. SPI-2 genes seem to contribute significantly to the increased replication.

The heat shock response of Mycobacterium tuberculosis: linking gene expression, immunology and pathogenesis

The regulation of heat shock protein (HSP) expression is critically important to pathogens such as Mycobacterium tuberculosis and dysregulation of the heat shock response results in increased immune recognition of the bacterium and reduced survival during chronic infection. In this study we use a whole genome spotted microarray to characterize the heat shock response of M. tuberculosis. We also begin a dissection of this important stress response by generating deletion mutants that lack specific transcriptional regulators and examining their transcriptional profiles under different stresses. Understanding the stimuli and mechanisms that govern heat shock in mycobacteria will allow us to relate observed in vivo expression patterns of HSPs to particular stresses and physiological conditions. The mechanisms controlling HSP expression also make attractive drug targets as part of a strategy designed to enhance immune recognition of the bacterium.

Wolbachia interferes with ferritin expression and iron metabolism in insects

Wolbachia is an intracellular bacterium generally described as being a facultative reproductive parasite. However, Wolbachia is necessary for oogenesis completion in the wasp Asobara tabida. This dependence has evolved recently as a result of interference with apoptosis during oogenesis. Through comparative transcriptomics between symbiotic and aposymbiotic individuals, we observed a differential expression of ferritin, which forms a complex involved in iron storage. Iron is an essential element that is in limited supply in the cell. However, it is also a highly toxic precursor of Reactive Oxygen Species (ROS). Ferritin has also been shown to play a key role in host-pathogen interactions. Measuring ferritin by quantitative RT-PCR, we confirmed that ferritin was upregulated in aposymbiotic compared to symbiotic individuals. Manipulating the iron content in the diet, we showed that iron overload markedly affected wasp development and induced apoptotic processes during oogenesis in A. tabida, suggesting that the regulation of iron homeostasis may also be related to the obligate dependence of the wasp. Finally, we demonstrated that iron metabolism is influenced by the presence of Wolbachia not only in the obligate mutualism with A. tabida, but also in facultative parasitism involving Drosophila simulans and in Aedes aegypti cells. In these latter cases, the expression of Wolbachia bacterioferritin was also increased in the presence of iron, showing that Wolbachia responds to the concentration of iron. Our results indicate that Wolbachia may generally interfere with iron metabolism. The high affinity of Wolbachia for iron might be due to physiological requirement of the bacterium, but it could also be what allows the symbiont to persist in the organism by reducing the labile iron concentration, thus protecting the cell from oxidative stress and apoptosis. These findings also reinforce the idea that pathogenic, parasitic and mutualistic intracellular bacteria all use the same molecular mechanisms to survive and replicate within host cells. By impacting the general physiology of the host, the presence of a symbiont may select for host compensatory mechanisms, which extends the possible consequences of persistent endosymbiont on the evolution of their hosts.

Trypanosoma carassii hsp70 increases expression of inflammatory cytokines and chemokines in macrophages of the goldfish (Carassius auratus L.)

We report on the cloning and characterization of Trypanosoma carassii 70 KDa heat shock protein (hsp70). T. carassii hsp70 was secreted/excreted into culture medium in vitro and was recognized by sera from infected fish. Recombinant hsp70 (rhsp70) activated goldfish macrophages and stimulated the production of pro-inflammatory cytokines including interferon gamma (IFNgamma), tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, (IL)-12 and chemokines CCL-1 and CXCL-8 (IL-8). T. carassii hsp70-induced cytokine expression was abrogated by pronase treatment of macrophages confirming the existence of receptor(s) on goldfish macrophage surface that recognize parasite molecule. Parasite hsp70 also up-regulated the expression inducible nitric oxide synthase (iNOS) isoforms A and B and induced a strong nitric oxide response of goldfish macrophages.

Stress, sublethal injury, resuscitation, and virulence of bacterial foodborne pathogens

Environmental stress and food preservation methods (e.g., heating, chilling, acidity, and alkalinity) are known to induce adaptive responses within the bacterial cell. Microorganisms that survive a given stress often gain resistance to that stress or other stresses via cross-protection. The physiological state of a bacterium is an important consideration when studying its response to food preservation techniques. This article reviews the various definitions of injury and stress, sublethal injury of bacteria, stresses that cause this injury, stress adaptation, cellular repair and response mechanisms, the role of reactive oxygen species in bacterial injury and resuscitation, and the potential for cross-protection and enhanced virulence as a result of various stress conditions.

Sigma32-mediated negative regulation of Salmonella pathogenicity island 1 expression

Salmonella pathogenicity island 1 (SPI1) enables infecting salmonellae to invade the intestinal epithelium and induce a proinflammatory response and macrophage cell death. SPI1 expression is controlled by a complex cascade with several transcriptional regulators within the island and global regulators outside it. Previously, we reported that DnaK-depleted salmonellae could neither invade epithelial cells nor secrete SPI1-encoded proteins, suggesting that DnaK is involved in the expression of SPI1. Here, we found that DnaK is involved in SPI1 expression through inhibition of sigma(32) protein, which directs the transcription of a group of genes in response to various global stresses. Overproduction of sigma(32) resulted in decreased levels of the SPI1-specific transcriptional regulators HilD and HilA. Further analysis demonstrated that the sigma(32)-mediated system negatively regulates HilD and HilA at the posttranslational and transcriptional levels, respectively. The executioner of this negative regulation was shown to be a sigma(32)-induced protein ATP-dependent Lon protease, which specifically degrades HilD. Since HilD can activate hilA transcription, is at the top of the hierarchical SPI1 regulatory loop, and has a dominant role, the posttranslational control of HilD by Lon is critically important for precise expression of SPI1. Consequently, we suggest that SPI1 expression is controlled by the feedback regulatory loop in which sigma(32) induces Lon to control turnover of HilD, and DnaK, which inhibits sigma(32) function, leading to the modulation of lon expression. This regulation in response to a specific combination of environmental signals would ensure that SPI1 expression is restricted to a few specific locations in the host.

Genome-wide screen for temperature-regulated genes of the obligate intracellular bacterium, Rickettsia typhi

Background

The ability of rickettsiae to survive in multiple eukaryotic host environments provides a good model for studying pathogen-host molecular interactions. Rickettsia typhi, the etiologic agent of murine typhus, is a strictly intracellular gram negative α-proteobacterium, which is transmitted to humans by its arthropod vector, the oriental rat flea, Xenopsylla cheopis. Thus, R. typhi must cycle between mammalian and flea hosts, two drastically different environments. We hypothesize that temperature plays a role in regulating host-specific gene expression, allowing R. typhi to survive in mammalian and arthropod hosts. In this study, we used Affymetrix microarrays to screen for temperature-induced genes upon a temperature shift from 37°C to 25°C, mimicking the two different host temperatures in vitro.

Results

Temperature-responsive genes belonged to multiple functional categories including among others, transcription, translation, posttranslational modification/protein turnover/chaperones and intracellular trafficking and secretion. A large number of differentially expressed genes are still poorly characterized, and either have no known function or are not in the COG database. The microarray results were validated with quantitative real time RT-PCR.

Conclusion

This microarray screen identified various genes that were differentially expressed upon a shift in temperature from 37°C to 25°C. Further characterization of the identified genes may provide new insights into the ability of R. typhi to successfully transition between its mammalian and arthropod hosts.