Current vaccine strategies and novel approaches to combatting Francisella infection

Tularemia is caused by subspecies of Francisella tularensis and can manifest in a variety of disease states, with the pneumonic presentation resulting in the greatest mortality. Despite decades of research, there are no approved vaccines against F. tularensis in the United States. Traditional vaccination strategies, such as live-attenuated or subunit vaccines, are not favorable due to inadequate protection or safety concerns. Because of this, novel vaccination strategies are needed to combat tularemia. Here we discuss the current state of and challenges to the tularemia vaccine field and suggest novel vaccine approaches going forward that might be better suited for protecting against F. tularensis infection.

Spectrum of activity of Salmonella anti-biofilm compounds: Evaluation of activity against biofilm-forming ESKAPE pathogens

The ESKAPE pathogens are a group of bacteria that are a leading cause of health-care associated infections and are known to be agents of chronic, biofilm-mediated infections. These chronic bacterial infections often respond poorly to antibiotics and in some cases may require surgical intervention in order to cure the infection. As biofilms are often the critical mediator of a chronic infection, it is essential to develop therapies that target bacteria within the biofilm state. Herein, we report the development of a rapid, 96-well plate-based assay that employs conditions specific for each species to optimize biofilm production and allow for easy identification of differences in biofilm mass after treatment with anti-biofilm candidates. We used these ESKAPE-specific biofilm assays to test our previously identified Salmonella anti-biofilm small molecule compounds, JG-1 and M4, for anti-biofilm activity. The results demonstrated that JG-1 and M4 have anti-biofilm activity against Enterobacter spp., S. aureus, E. faecium, P. aeruginosa, and A. baumannii. In addition, we identified that M4 has significant antimicrobial activity against S. aureus and E. faecium at concentrations >10 μM (X μg/mL). These findings support the claim that JG-1 and M4 have broad-spectrum anti-biofilm activity, while M4 has antimicrobial activity against the Gram-positive members of the ESKAPE pathogens. Thus, these compounds have the potential to have a significant impact on treating multiple types of commonly encountered biofilm-mediated infections.

Invasive Non-Typhoidal Salmonella Lineage Biofilm Formation and Gallbladder Colonization Vary But Do Not Correlate Directly with Known Biofilm-Related Mutations

Non-typhoidal Salmonella (NTS) serovars have a broad host range and cause gastroenteritis in humans. However, invasive NTS (iNTS) bloodstream infections have increased in the last decade, causing 60,000 deaths annually. Human-specific typhoidal Salmonella colonizes and forms biofilms on gallstones, resulting in chronic, asymptomatic infection. iNTS lineages are undergoing genomic reduction and may have adapted to person-to-person transmission via mutations in virulence, bile resistance, and biofilm formation. As such, we sought to determine the capacity of iNTS lineages for biofilm formation and the development of chronic infections in the gallbladder in our mouse model. Of the lineages tested (L1, L2, L3 and UK), only L2 and UK were defective for the rough, dry and red (RDAR) morphotype, correlating with the known bcsG (cellulose) mutation but not with csgD (curli) gene mutations. Biofilm-forming ability was assessed in vitro, which revealed a biofilm formation hierarchy of L3 > ST19 > UK > L1 = L2, which did not correlate directly with either the bcsG or the csgD mutation. By confocal microscopy, biofilms of L2 and UK had significantly less curli and cellulose, while L1 biofilms had significantly lower cellulose. All iNTS strains were able to colonize the mouse gallbladder, liver, and spleen in a similar manner, while L3 had a significantly higher bacterial load in the gallbladder and increased lethality. While there was iNTS lineage variability in biofilm formation, gallbladder colonization, and virulence in a chronic mouse model, all tested lineages were capable of colonization despite possessing biofilm-related mutations. Thus, iNTS strains may be unrecognized chronic pathogens in endemic settings.

An E. coli display method for characterization of peptide-sensor kinase interactions

Bacteria use two-component system (TCS) signaling pathways to sense and respond to peptides involved in host defense, quorum sensing and inter-bacterial warfare. However, little is known about the broad peptide-sensing capabilities of TCSs. In this study, we developed an Escherichia coli display method to characterize the effects of human antimicrobial peptides (AMPs) on the pathogenesis-regulating TCS PhoPQ of Salmonella Typhimurium with much higher throughput than previously possible. We found that PhoPQ senses AMPs with diverse sequences, structures and biological functions. We further combined thousands of displayed AMP variants with machine learning to identify peptide sub-domains and biophysical features linked to PhoPQ activation. Most of the newfound AMP activators induce PhoPQ in S. Typhimurium, suggesting possible roles in virulence regulation. Finally, we present evidence that PhoPQ peptide-sensing specificity has evolved across commensal and pathogenic bacteria. Our method enables new insights into the specificities, mechanisms and evolutionary dynamics of TCS-mediated peptide sensing in bacteria.

Integrating carbon stocks and landscape connectivity for nature-based climate solutions

Actions to protect against biodiversity loss and climate change will require a framework that addresses synergies between these interrelated issues. In this study, we present methods for identifying areas important for the implementation of nature-based climate solutions and biodiversity conservation by intersecting high-resolution spatial data for carbon storage and landscape connectivity. We explored the spatial congruence of carbon and connectivity in Ontario, Canada and examined effectiveness of current protected areas coverage. We found a weak positive relationship between carbon stocks and landscape connectivity; however, our maps revealed large hotspots, with high values of both indices, throughout the boreal forest and northern peatlands and smaller, isolated hotspots, in the settled landscapes of the south. Location of hotspots varied depending on whether we considered forest or soil carbon. Further, our results show that current protected and conserved areas in Ontario only cover 13% of landscapes with the highest values for both carbon storage and connectivity. Protection or restoration of areas that maximize the co-benefits of carbon storage and connectivity would make significant contributions toward ambitious national targets to reduce greenhouse gas emissions and conserve biodiversity.

The Effect of the Gallbladder Environment during Chronic Infection on Salmonella Persister Cell Formation

Typhoid fever is caused by Salmonella enterica serovar Typhi (S. Typhi). Around 3-5% of individuals infected become chronic carriers, with the gallbladder (GB) as the predominant site of persistence. Gallstones (GS) aid in the development and maintenance of GB carriage, serving as a substrate to which Salmonellae attach and form a biofilm. This biofilm matrix protects bacteria from the host immune system and environmental stress. This shielded environment is an ideal place for the development of persister cells, a transient phenotype of a subset of cells within a population that allows survival after antibiotic treatment. Persisters can also arise in response to harsh environments such as the GB. Here we investigate if GB conditions affect the number of persisters in a Salmonella population. To simulate the chronic GB environment, we cultured biofilms in cholesterol-coated 96-well plates in the presence of ox or human bile. We then treated planktonic or biofilm Salmonella cultures with high concentrations of different antibiotics. This study suggests that biofilms provide a niche for persister cells, but GB conditions either play no role or have a negative influence on persister formation, especially after kanamycin treatment. The antibiotic target was important, as antimicrobials directed against DNA replication or the cell wall had no effect on persister cell formation. Interestingly, repeated treatment with ciprofloxacin increased the percentage of S. Typhimurium persisters in a biofilm, but this increase was abolished by GB conditions. On the other hand, repeated ciprofloxacin treatment of S. Typhi biofilms in GB conditions slightly increased the fraction of persisters. Thus, while the harsh conditions in the GB would be thought to give rise to increased persisters, therefore contributing to the development of chronic carriage, these data suggest persister cell formation is dampened in this environment.

L-Arabinose Transport and Metabolism in Salmonella Influences Biofilm Formation

L-arabinose inducible promoters are commonly used in gene expression analysis. However, nutrient source and availability also play a role in biofilm formation; therefore, L-arabinose metabolism could impact biofilm development. In this study we examined the impact of L-arabinose on Salmonella enterica serovar Typhimurium (S. Typhimurium) biofilm formation. Using mutants impaired for the transport and metabolism of L-arabinose, we showed that L-arabinose metabolism negatively impacts S. Typhimurium biofilm formation in vitro. When L-arabinose metabolism is abrogated, biofilm formation returned to baseline levels. However, without the ability to import extracellular L-arabinose, biofilm formation significantly increased. Using RNA-Seq we identified several gene families involved in these different phenotypes including curli expression, amino acid synthesis, and L-arabinose metabolism. Several individual candidate genes were tested for their involvement in the L-arabinose-mediated biofilm phenotypes, but most played no significant role. Interestingly, in the presence of L-arabinose the diguanylate cyclase gene adrA was downregulated in wild type S. Typhimurium. Meanwhile cyaA, encoding an adenylate cyclase, was downregulated in an L-arabinose transport mutant. Using an IPTG-inducible plasmid to deplete c-di-GMP via vieA expression, we were able to abolish the increased biofilm phenotype seen in the transport mutant. However, the mechanism by which the L-arabinose import mutant forms significantly larger biofilms remains to be determined. Regardless, these data suggest that L-arabinose metabolism influences intracellular c-di-GMP levels and therefore biofilm formation. These findings are important when considering the use of an L-arabinose inducible promoter in biofilm conditions.

Salmonella Biofilms Tolerate Hydrogen Peroxide by a Combination of Extracellular Polymeric Substance Barrier Function and Catalase Enzymes

The ability of Salmonella enterica subspecies enterica serovar Typhi (S. Typhi) to cause chronic gallbladder infections is dependent on biofilm growth on cholesterol gallstones. Non-typhoidal Salmonella (e.g. S. Typhimurium) also utilize the biofilm state to persist in the host and the environment. How the pathogen maintains recalcitrance to the host response, and oxidative stress in particular, during chronic infection is poorly understood. Previous experiments demonstrated that S. Typhi and S. Typhimurium biofilms are tolerant to hydrogen peroxide (H₂O₂), but that mutations in the biofilm extracellular polymeric substances (EPSs) O antigen capsule, colanic acid, or Vi antigen reduce tolerance. Here, biofilm-mediated tolerance to oxidative stress was investigated using a combination of EPS and catalase mutants, as catalases are important detoxifiers of H₂O₂. Using co-cultured biofilms of wild-type (WT) bacteria with EPS mutants, it was demonstrated that colanic acid in S. Typhimurium and Vi antigen in S. Typhi have a community function and protect all biofilm-resident bacteria rather than to only protect the individual cells producing the EPSs. However, the H₂O₂ tolerance deficiency of a O antigen capsule mutant was unable to be compensated for by co-culture with WT bacteria. For curli fimbriae, both WT and mutant strains are tolerant to H₂O₂ though unexpectedly, co-cultured WT/mutant biofilms challenged with H₂O₂ resulted in sensitization of both strains, suggesting a more nuanced oxidative resistance alteration in these co-cultures. Three catalase mutant (katE, katG and a putative catalase) biofilms were also examined, demonstrating significant reductions in biofilm H₂O₂ tolerance for the katE and katG mutants. Biofilm co-culture experiments demonstrated that catalases exhibit a community function. We further hypothesized that biofilms are tolerant to H₂O₂ because the physical barrier formed by EPSs slows penetration of H₂O₂ into the biofilm to a rate that can be mitigated by intra-biofilm catalases. Compared to WT, EPS-deficient biofilms have a heighted response even to low-dose (2.5 mM) H₂O₂ challenge, confirming that resident bacteria of EPS-deficient biofilms are under greater stress and have limited protection from H₂O₂. Thus, these data provide an explanation for how Salmonella achieves tolerance to H₂O₂ by a combination of an EPS-mediated barrier and enzymatic detoxification.

Is Upregulation of Sarcolipin Beneficial or Detrimental to Muscle Function?

Sarcolipin (SLN) is a regulator of sarco/endo plasmic reticulum Ca²⁺-ATPase (SERCA) pump and has been shown to be involved in muscle nonshivering thermogenesis (NST) and energy metabolism. Interestingly, SLN expression is significantly upregulated both during muscle development and in several disease states. However, the significance of altered SLN expression in muscle patho-physiology is not completely understood. We have previously shown that transgenic over-expression of SLN in skeletal muscle is not detrimental, and can promote oxidative metabolism and exercise capacity. In contrast, some studies have suggested that SLN upregulation in disease states is deleterious for muscle function and ablation of SLN can be beneficial. In this perspective article, we critically examine both published and some new data to determine the relevance of SLN expression to disease pathology. The new data presented in this paper show that SLN levels are induced in muscle during systemic bacterial (Salmonella) infection or lipopolysaccharides (LPS) treatment. We also present data showing that SLN expression is significantly upregulated in different types of muscular dystrophies including myotubular myopathy. These data taken together reveal that upregulation of SLN expression in muscle disease is progressive and increases with severity. Therefore, we suggest that increased SLN expression should not be viewed as the cause of the disease; rather, it is a compensatory response to meet the higher energy demand of the muscle. We interpret that higher SLN/SERCA ratio positively modulate cytosolic Ca²⁺ signaling pathways to promote mitochondrial biogenesis and oxidative metabolism to meet higher energy demand in muscle.

Listeria monocytogenes upregulates mitochondrial calcium signalling to inhibit LC3-associated phagocytosis as a survival strategy

Mitochondria are believed to have originated ~2.5 billion years ago. As well as energy generation in cells, mitochondria have a role in defence against bacterial pathogens. Despite profound changes in mitochondrial morphology and functions following bacterial challenge, whether intracellular bacteria can hijack mitochondria to promote their survival remains elusive. We report that Listeria monocytogenes-an intracellular bacterial pathogen-suppresses LC3-associated phagocytosis (LAP) by modulation of mitochondrial Ca²⁺ (mtCa²⁺) signalling in order to survive inside cells. Invasion of macrophages by L. monocytogenes induced mtCa²⁺ uptake through the mtCa²⁺ uniporter (MCU), which in turn increased acetyl-coenzyme A (acetyl-CoA) production by pyruvate dehydrogenase. Acetylation of the LAP effector Rubicon with acetyl-CoA decreased LAP formation. Genetic ablation of MCU attenuated intracellular bacterial growth due to increased LAP formation. Our data show that modulation of mtCa²⁺ signalling can increase bacterial survival inside cells, and highlight the importance of mitochondrial metabolism in host-microbial interactions.

Salmonella Biofilm Formation, Chronic Infection, and Immunity Within the Intestine and Hepatobiliary Tract

Within the species of Salmonella enterica, there is significant diversity represented among the numerous subspecies and serovars. Collectively, these account for microbes with variable host ranges, from common plant and animal colonizers to extremely pathogenic and human-specific serovars. Despite these differences, many Salmonella species find commonality in the ability to form biofilms and the ability to cause acute, latent, or chronic disease. The exact outcome of infection depends on many factors such as the growth state of Salmonella, the environmental conditions encountered at the time of infection, as well as the infected host and immune response elicited. Here, we review the numerous biofilm lifestyles of Salmonella (on biotic and abiotic surfaces) and how the production of extracellular polymeric substances not only enhances long-term persistence outside the host but also is an essential function in chronic human infections. Furthermore, careful consideration is made for the events during initial infection that allow for gut transcytosis which, in conjunction with host immune functions, often determine the progression of disease. Both typhoidal and non-typhoidal salmonellae can cause chronic and/or secondary infections, thus the adaptive immune responses to both types of bacteria are discussed with particular attention to the differences between Salmonella Typhi, Salmonella Typhimurium, and invasive non-typhoidal Salmonella that can result in differential immune responses. Finally, while strides have been made in our understanding of immunity to Salmonella in the lymphoid organs, fewer definitive studies exist for intestinal and hepatobiliary immunity. By examining our current knowledge and what remains to be determined, we provide insight into new directions in the field of Salmonella immunity, particularly as it relates to chronic infection.

Enhanced biofilm and extracellular matrix production by chronic carriage versus acute isolates of Salmonella Typhi

Salmonella Typhi is the primary causative agent of typhoid fever; an acute systemic infection that leads to chronic carriage in 3–5% of individuals. Chronic carriers are asymptomatic, difficult to treat and serve as reservoirs for typhoid outbreaks. Understanding the factors that contribute to chronic carriage is key to development of novel therapies to effectively resolve typhoid fever. Herein, although we observed no distinct clustering of chronic carriage isolates via phylogenetic analysis, we demonstrated that chronic isolates were phenotypically distinct from acute infection isolates. Chronic carriage isolates formed significantly thicker biofilms with greater biomass that correlated with significantly higher relative levels of extracellular DNA (eDNA) and DNABII proteins than biofilms formed by acute infection isolates. Importantly, extracellular DNABII proteins include integration host factor (IHF) and histone-like protein (HU) that are critical to the structural integrity of bacterial biofilms. In this study, we demonstrated that the biofilm formed by a chronic carriage isolate in vitro, was susceptible to disruption by a specific antibody against DNABII proteins, a successful first step in the development of a therapeutic to resolve chronic carriage.

Salmonella Typhi, a human restricted pathogen is the primary etiologic agent of typhoid fever, an acute systemic infection that has a global incidence of 21 million cases annually. Although the acute infection is resolved by antibiotics, 3–5% of individuals develop chronic carriage that is difficult to resolve with antibiotics. A majority of these indivuals serve as reservoirs for further spread of the disease. Understanding the differences between acute and chronic carrier strains is key to design novel targeted approaches to undermine carriage. Here, we demonstrated that chronic carrier strains although not genotypically distinct from acute strains, formed thicker biofilms with greater relative levels of extracellular eDNA and DNABII proteins than those formed by acute infection isolates. We also demonstrated that an antibody against DNABII proteins significantly disrupted biofilms formed by a chronic carrier strain and therefore supported development of therapeutic use of this antibody to attenuate chronic carriage.

In Vitro Evaluation of Anti-biofilm Agents Against Salmonella enterica

Salmonella enterica is able to establish robust adherent communities called biofilms that allow for long-term colonization of both biotic and abiotic surfaces. These biofilm communities pose a significant challenge to successful eradication of the bacteria from contaminated surfaces and the infected host, as entry into the biofilm phenotype confers the bacterial population with tolerance to a variety of environmental and therapeutic insults to which it would otherwise be susceptible. The identification of antimicrobial strategies that specifically target the Salmonella biofilm state is therefore of great importance in order to both prevent and treat biofilm-mediated disease. Here, we provide detailed methods for the in vitro cultivation of Salmonella biofilms that can easily be scaled up for use in high-throughput screening of candidate anti-biofilm agents. These assays may also be utilized to further characterize the inhibitory and/or disruptive capabilities of lead anti-biofilm agents, as well as to identify combination treatments that demonstrate enhanced anti-biofilm effects. Furthermore, the assays may be slightly modified (e.g., optimal growth conditions) to evaluate other bacterial genera.

A dual-therapy approach for the treatment of biofilm-mediated Salmonella gallbladder carriage

Asymptomatic carriage of Salmonella Typhi continues to facilitate the transmission of typhoid fever, resulting in 14 million new infections and 136,000 fatalities each year. Asymptomatic chronic carriage of S. Typhi is facilitated by the formation of biofilms on gallstones that protect the bacteria from environmental insults and immune system clearance. Here, we identified two unique small molecules capable of both inhibiting Salmonella biofilm growth and disrupting pre-formed biofilm structures without affecting bacterial viability. In a mouse model of chronic gallbladder Salmonella carriage, treatment with either compound reduced bacterial burden in the gallbladder by 1–2 logs resulting in bacterial dissemination to peripheral organs that was associated with increased mortality. Co-administration of either compound with ciprofloxacin not only enhanced compound efficacy in the gallbladder by a further 1–1.5 logs for a total of 3–4.5 log reduction, but also prevented bacterial dissemination to peripheral organs. These data suggest a dual-therapy approach targeting both biofilm and planktonic populations can be further developed as a safe and efficient treatment of biofilm-mediated chronic S. Typhi infections.

Typhoid fever is an infectious disease caused by Salmonella Typhi (S. Typhi), a bacterium that causes as many as 14 million new infections and 136,000 deaths annually. Asymptomatic chronic carriers of S. Typhi play a major role in the transmission of typhoid fever, as they intermittently shed the bacteria and can unknowingly infect surrounding individuals. Here, we characterized novel compounds that target biofilm formation, a process utilized by S. Typhi to establish and maintain chronic carriage in the gallbladder, in hopes that they may be eventually used in conjunction with traditional antibiotics to prevent and/or cure chronic infections more efficiently than antibiotics alone.

Sequential ubiquitination of NLRP3 by RNF125 and Cbl-b limits inflammasome activation and endotoxemia

Aberrant NLRP3 inflammasome activation contributes to the development of endotoxemia. The importance of negative regulation of NLRP3 inflammasomes remains poorly understood. Here, we show that the E3 ubiquitin ligase Cbl-b is essential for preventing endotoxemia induced by a sub-lethal dose of LPS via a caspase-11/NLRP3-dependent manner. Further studies show that NLRP3 undergoes both K63- and K48-linked polyubiquitination. Cbl-b binds to the K63-ubiquitin chains attached to the NLRP3 leucine-rich repeat domain (LRR) via its ubiquitin-associated region (UBA) and then targets NLRP3 at K496 for K48-linked ubiquitination and proteasome-mediated degradation. We also identify RNF125 as an additional E3 ubiquitin ligase that initiates K63-linked ubiquitination of the NLRP3 LRR domain. Therefore, NLRP3 is sequentially ubiquitinated by K63- and K48-linked ubiquitination, thus keeping the NLRP3 inflammasomes in check and restraining endotoxemia.

Accurate and Efficient Determination of Unknown Metabolites in Metabolomics by NMR-Based Molecular Motif Identification

Knowledge of the chemical identity of metabolite molecules is critical for the understanding of the complex biological systems to which they belong. Since metabolite identities and their concentrations are often directly linked to the phenotype, such information can be used to map biochemical pathways and understand their role in health and disease. A very large number of metabolites however are still unknown; i.e., their spectroscopic signatures do not match those in existing databases, suggesting unknown molecule identification is both imperative and challenging. Although metabolites are structurally highly diverse, the majority shares a rather limited number of structural motifs, which are defined by sets of ¹H and ¹³C chemical shifts of the same spin system. This allows one to characterize unknown metabolites by a divide-and-conquer strategy that identifies their structural motifs first. Here, we present the structural motif-based approach "SUMMIT Motif" for the de novo identification of unknown molecular structures in complex mixtures, without the need for extensive purification, using NMR in tandem with two newly curated NMR molecular structural motif metabolomics databases (MSMMDBs). For the identification of structural motif(s), first, the ¹H and ¹³C chemical shifts of all the individual spin systems are extracted from 2D and 3D NMR spectra of the complex mixture. Next, the molecular structural motifs are identified by querying these chemical shifts against the new MSMMDBs. One database, COLMAR MSMMDB, was derived from experimental NMR chemical shifts of known metabolites taken from the COLMAR metabolomics database, while the other MSMMDB, pNMR MSMMDB, is based on predicted chemical shifts of metabolites of several existing large metabolomics databases. For molecules consisting of multiple spin systems, spin systems are connected via long-range scalar J-couplings. When this motif-based identification method was applied to the hydrophilic extract of mouse bile fluid, two unknown metabolites could be successfully identified. This approach is both accurate and efficient for the identification of unknown metabolites and hence enables the discovery of new biochemical processes and potential biomarkers.

Two-Component Systems in Francisella Species

Bacteria alter gene expression in response to changes in their environment through various mechanisms that include signal transduction systems. These signal transduction systems use membrane histidine kinase with sensing domains to mediate phosphotransfer to DNA-binding proteins that alter the level of gene expression. Such regulators are called two-component systems (TCSs). TCSs integrate external signals and information from stress pathways, central metabolism and other global regulators, thus playing an important role as part of the overall regulatory network. This review will focus on the knowledge of TCSs in the Gram-negative bacterium, Francisella tularensis, a biothreat agent with a wide range of potential hosts and a significant ability to cause disease. While TCSs have been well-studied in several bacterial pathogens, they have not been well-studied in non-model organisms, such as F. tularensis and its subspecies, whose canonical TCS content surprisingly ranges from few to none. Additionally, of those TCS genes present, many are orphan components, including KdpDE, QseC, QseB/PmrA, and an unnamed two-component system (FTN_1452/FTN_1453). We discuss recent advances in this field related to the role of TCSs in Francisella physiology and pathogenesis and compare the TCS genes present in human virulent versus. environmental species and subspecies of Francisella.

Structural variants of Salmonella Typhimurium lipopolysaccharide induce less dimerization of TLR4/MD-2 and reduced pro-inflammatory cytokine production in human monocytes

Salmonella enterica serovar Typhimurium (S. Typhimurium) changes the structure of its lipopolysaccharide (LPS) in response to the environment. The two main LPS variants found in S. Typhimurium correspond to LPS with a hepta-acylated lipid A (LPS 430) and LPS with modified phosphate groups on its lipid A (LPS 435). We have previously shown that these modified LPS have a lower capacity than wild type (WT) LPS to induce the production of pro-inflammatory cytokines in mice. Nevertheless, it is not know if LPS 430 and LPS 435 could also subvert the innate immune responses in human cells. In this study, we found that LPS 430 and LPS 435 were less efficient than WT LPS to induce the production of pro-inflammatory cytokines by human monocytes, in addition we found a decreased dimerization of the TLR4/MD-2 complex in response to LPS 430, suggesting that structurally modified LPS are sensed differently than WT LPS by this receptor; however, LPS 430 and 435 induced similar activation of the transcription factors NF-κB p65, IRF3, p38 and ERK1/2 than WT LPS. Microarray analysis of LPS 430- and LPS 435-activated monocytes revealed a gene transcription profile with differences only in the expression levels of microRNA genes compared to the profile induced by WT LPS, suggesting that the lipid A modifications present in LPS 430 and LPS 435 have a moderate effect on the activation of the human TLR4/MD-2 complex. Our results are relevant to understand LPS modulation of immune responses and this knowledge could be useful for the development of novel adjuvants and immunomodulators.

Identification of a Small Molecule Anti-biofilm Agent Against Salmonella enterica

Biofilm formation is a common strategy utilized by bacterial pathogens to establish persistence in a host niche. Salmonella enterica serovar Typhi, the etiological agent of Typhoid fever, relies on biofilm formation in the gallbladder to chronically colonize asymptomatic carriers, allowing for transmission to uninfected individuals. S. enterica serovar Typhimurium utilizes biofilms to achieve persistence in human and animal hosts, an issue of both clinical and agricultural importance. Here, we identify a compound that selectively inhibits biofilm formation in both S. Typhi and S. Typhimurium serovars at early stages of biofilm development with an EC₅₀ of 21.0 and 7.4 μM, respectively. We find that this compound, T315, also reduces biofilm formation in Acinetobacter baumannii, a nosocomial and opportunistic pathogen with rising antibiotic resistance. T315 treatment in conjunction with sub-MIC dosing of ciprofloxacin further reduces S. enterica biofilm formation, demonstrating the potential of such combination therapies for therapeutic development. Through synthesis of two biotin-labeled T315 probes and subsequent pull-down and proteomics analysis, we identified a T315 binding target: WrbA, a flavin mononucleotide-dependent NADH:quinone oxidoreductase. Using a S. Typhimurium strain lacking WrbA we demonstrate that this factor contributes to endogenous S. enterica biofilm formation processes and is required for full T315 anti-biofilm activity. We suggest WrbA as a promising target for further development of anti-biofilm agents in Salmonella, with potential for use against additional bacterial pathogens. The development of anti-biofilm therapeutics will be essential to combat chronic carriage of Typhoid fever and thus accomplish a meaningful reduction of global disease burden.

In Vivo and Cellular Trafficking of Acetalated Dextran Microparticles for Delivery of a Host-Directed Therapy for Salmonella enterica Serovar Typhi Infection

Previously we have encapsulated host-directed therapy AR-12 into acetalated dextran (Ace-DEX) microparticles (MPs) to mitigate drug toxicity and passively target phagocytic host cells. Herein, we have improved upon our initial emulsion-based formulation of Ace-DEX MPs encapsulating AR-12 (AR-12/MPs) by improving the drug encapsulation efficiency, evaluating sterilization processes for manufacturing, and understanding cellular and in vivo trafficking of the MPs. By using an alternative solvent system, ethyl acetate, we report an increased encapsulation efficiency of AR-12 while maintaining the pH-responsive degradation kinetics of Ace-DEX MPs. To better manufacture this novel antimicrobial formulation, we sterilized AR-12/MPs by gamma irradiation or ethylene oxide and evaluated their efficacy against intracellular Salmonella enterica serovar Typhi. Sterilized AR-12/MPs resulted in a significant reduction in intracellular bacterial burden compared to Blank/MPs. We also characterized intracellular trafficking of Ace-DEX MPs encapsulating fluorophores, which demonstrated internalization of MPs in endo/lysosomal compartments and time and degradation-rate dependent lysosomal escape into cytosolic compartments. Additionally, in vivo toxicity was mitigated following encapsulation of AR-12, where the maximum tolerated dose of AR-12 was increased compared to soluble treatment via intranasal, intravenous, and intraperitoneal administration routes. Following in vivo trafficking of Ace-DEX MPs via the same routes, intranasal administration demonstrated the highest accumulation in the lungs, liver, and kidneys, which persisted out to 240 h. Overall, we have advanced the formulation of this host-directed therapy and broadened the understanding of Ace-DEX MP delivery.

2-Aminobenzimidazoles as antibiofilm agents against Salmonella enterica serovar Typhimurium

Serovars within the species Salmonella enterica are some of the most common food and water-borne pathogens worldwide. Some S. enterica serovars have shown a remarkable ability to persist both inside and outside the human body. Salmonella enterica serovar Typhi can cause chronic, asymptomatic infection of the human gallbladder. This organism's ability to survive inside the gallbladder centers around its ability to form biofilms on gallstone surfaces. Currently, chronic carriage of S. Typhi is treated by invasive methods, which are not well suited to areas where Salmonella carriage is prevalent. Herein, we report 2-aminobenzimidazoles that inhibit S. enterica serovar Typhimurium (a surrogate for S. Typhi) biofilm formation in low micromolar concentrations. Modifications to the head, tail, and linker regions of the original hit compound elucidated new, more effective analogues that inhibit S. Typhimurium biofilm formation while being non-toxic to planktonic bacterial growth.

Phenotypic and genotypic characterization of temporally related nontyphoidal Salmonella strains isolated from humans and food animals in central Ethiopia

Salmonella is one of the common causes of food-borne bacterial illnesses. The primary sources of human nontyphoidal Salmonella (NTS) infection are food animals. This study characterized temporally and spatially related Salmonella isolated during April 2013 to March 2014 from faeces of diarrhoeic human patients in Addis Ababa (n = 68) and food animals (n = 84) in Addis Ababa and surrounding districts (dairy cattle, n = 30; slaughtered cattle, n = 20; poultry, n = 26; swine n = 8). Isolates were serotyped, page typed and tested for antimicrobial susceptibility using Kirby-Bauer disc diffusion method, and genotyped by pulsed-field gel electrophoresis (PFGE). The dominant Salmonella serovars isolated from food animals were S. Saintpaul (38.1%), S. Typhimurium (17.9%) and S. Kentucky (9.5%), whereas in humans, S. Typhimurium (39.7%), S. Virchow (30.9%) and S. Kottbus (10.3%) were frequently isolated. Resistance to streptomycin, sulfisoxazole, tetracycline, ampicillin and cephalothin was higher in animal isolates than human isolates, and mean number of antimicrobials to which isolates were resistant was significantly higher in isolates from cattle and poultry compared to those from humans (p < 0.05). All S. Kentucky isolated from animals and humans were multidrug resistant (MDR) with shared resistance phenotype (AmpCfCipTeSuSNa). Although this study involved small sample size and was not able to show clear epidemiological linkage among isolates from various sources, genotyping by PFGE analysis demonstrated circulation of closely related genotypes of S. Virchow, S. Typhimurium and S. Kentucky among humans and food animals. Detection of related Salmonella isolates from humans and animals, the high MDR status of isolates from animals and close proximity of farms and human residential areas in the absence of appropriate biosecurity present major public health problem. Integrated surveillance of Salmonella serovars in humans and animals and implementation of appropriate hazard analysis and pathogen control strategies along critical points of the food chain from farm to table is recommended.

Chronic biofilm-based infections: skewing of the immune response

Many of the deadliest bacterial diseases that plague humanity in the modern age are caused by bacterial biofilms that produce chronic infections. However, most of our knowledge of the host immune response comes from the study of planktonic pathogens. While there are similarities in the host response to planktonic and biofilm bacteria, specific immune responses toward biofilms have not been well studied; the only apparent difference is the inability to clear the bacteria allowing the biofilm infection to become chronic. In some cases, the biofilms skew T-cell response toward a balance that allows a stalemate between the host and the pathogen, in which the infection can become persistent. In this minireview, we will summarize well-known examples of this phenomena as well as some emerging studies that may indicate that this situation is much more common than initially thought.

Biomedical Science Undergraduate Major: A New Pathway to Advance Research and the Health Professions

PROBLEM

Many students entering professional degree programs, particularly M.D., Ph.D., and M.D./Ph.D., are not well prepared regarding the breadth of scientific knowledge required, communication skills, research experience, reading and understanding the scientific literature, and significant shadowing (for M.D.-related professions). In addition, physician scientists are a needed and necessary part of the academic research environment but are dwindling in numbers.

INTERVENTION

In response to predictions of critical shortages of clinician investigators and the lack of proper preparation as undergraduates for these professions, the Biomedical Science (BMS) undergraduate major was created at The Ohio State University to attract incoming college freshmen with interests in scientific research and the healthcare professions. The intent of this major was to graduate an elite cohort of highly talented individuals who would pursue careers in the healthcare professions, biomedical research, or both.

CONTEXT

Students were admitted to the BMS major through an application and interview process. Admitted cohorts were small, comprising 22 to 26 students, and received a high degree of individualized professional academic advising and mentoring. The curriculum included a minimum of 4 semesters (or 2 years) of supervised research experience designed to enable students to gain skills in clinical and basic science investigation. In addition to covering the prerequisites for medicine and advanced degrees in health professions, the integrated BMS coursework emphasized research literacy as well as skills related to work as a healthcare professional, with additional emphasis on independent learning, teamwork to solve complex problems, and both oral and written communication skills. Supported by Ohio State's Department of Internal Medicine, a unique clinical internship provided selected students with insights into potential careers as physician scientists.

OUTCOME

In this educational case report, we describe the BMS undergraduate major and its outcomes after 10 years of implementation. Major outcomes include the strength of the major's matriculates (average ACT score = 32.6; average high school class percentile rank = 95.5) and the high percentage of BMS students who pursued graduate/professional degrees (91%; n = 110). Other markers of success include the strong focus on research, which resulted in 120 articles published by graduates to date (range = 0-12/student; 43% with at least 1 peer-reviewed journal article).

LESSONS LEARNED

Based on its successes, adoption of a similar program at other academic medical centers would help feed the pipeline of well-trained health professionals and biomedical researchers.

Biofilm Formation Protects Salmonella from the Antibiotic Ciprofloxacin In Vitro and In Vivo in the Mouse Model of chronic Carriage

Typhoid fever is caused by the human-restricted pathogen Salmonella enterica sv. Typhi. Approximately 5% of people that resolve the disease become chronic carriers, with the gallbladder as the main reservoir of the bacteria. Of these, about 90% present with gallstones, on which Salmonella form biofilms. Because S. Typhi is a human-restricted pathogen, these carriers are the main source of dissemination of the disease; unfortunately, antibiotic treatment has shown to be an ineffective therapy. This is believed to be caused by the inherent antibiotic resistance conferred by Salmonella biofilms growing on gallstones. The gallstone mouse model with S. Typhimurium has proven to be an excellent surrogate for S. Typhi chronic infection. In this study, we test the hypothesis that the biofilm state confers Salmonella with the increased resistance to antibiotics observed in cases of chronic carriage. We found that, in the biofilm state, Salmonella is significantly more resistant to ciprofloxacin, a common antibiotic used for the treatment of Salmonella, both in vitro (p < 0.001 for both S. Typhi and S. Typhimurium with respect to planktonic cells) and in vivo (p = 0.0035 with respect to control mice).

AR-13, a Celecoxib Derivative, Directly Kills Francisella In Vitro and Aids Clearance and Mouse Survival In Vivo

Francisella tularensis (F. tularensis) is the causative agent of tularemia and is classified as a Tier 1 select agent. No licensed vaccine is currently available in the United States and treatment of tularemia is confined to few antibiotics. In this study, we demonstrate that AR-13, a derivative of the cyclooxygenase-2 inhibitor celecoxib, exhibits direct in vitro bactericidal killing activity against Francisella including a type A strain of F. tularensis (SchuS4) and the live vaccine strain (LVS), as well as toward the intracellular proliferation of LVS in macrophages, without causing significant host cell toxicity. Identification of an AR-13-resistant isolate indicates that this compound has an intracellular target(s) and that efflux pumps can mediate AR-13 resistance. In the mouse model of tularemia, AR-13 treatment protected 50% of the mice from lethal LVS infection and prolonged survival time from a lethal dose of F. tularensis SchuS4. Combination of AR-13 with a sub-optimal dose of gentamicin protected 60% of F. tularensis SchuS4-infected mice from death. Taken together, these data support the translational potential of AR-13 as a lead compound for the further development of new anti-Francisella agents.

Genetic markers associated with resistance to beta-lactam and quinolone antimicrobials in non-typhoidal Salmonella isolates from humans and animals in central Ethiopia

Background

Beta-lactam and quinolone antimicrobials are commonly used for treatment of infections caused by non-typhoidal Salmonella (NTS) and other pathogens. Resistance to these classes of antimicrobials has increased significantly in the recent years. However, little is known on the genetic basis of resistance to these drugs in Salmonella isolates from Ethiopia.

Methods

Salmonella isolates with reduced susceptibility to beta-lactams (n = 43) were tested for genes encoding for beta-lactamase enzymes, and those resistant to quinolones (n = 29) for mutations in the quinolone resistance determining region (QRDR) as well as plasmid mediated quinolone resistance (PMQR) genes using PCR and sequencing.

Results

Beta-lactamase genes (bla) were detected in 34 (79.1%) of the isolates. The dominant bla gene was blaTEM, recovered from 33 (76.7%) of the isolates, majority being TEM-1 (24, 72.7%) followed by TEM-57, (10, 30.3%). The blaOXA-10 and blaCTX-M-15 were detected only in a single S. Concord human isolate. Double substitutions in gyrA (Ser83-Phe + Asp87-Gly) as well as parC (Thr57-Ser + Ser80-Ile) subunits of the quinolone resistance determining region (QRDR) were detected in all S. Kentucky isolates with high level resistance to both nalidixic acid and ciprofloxacin. Single amino acid substitutions, Ser83-Phe (n = 4) and Ser83-Tyr (n = 1) were also detected in the gyrA gene. An isolate of S. Miami susceptible to nalidixic acid but intermediately resistant to ciprofloxacin had Thr57-Ser and an additional novel mutation (Tyr83-Phe) in the parC gene. Plasmid mediated quinolone resistance (PMQR) genes investigated were not detected in any of the isolates. In some isolates with decreased susceptibility to ciprofloxacin and/or nalidixic acid, no mutations in QRDR or PMQR genes were detected. Over half of the quinolone resistant isolates in the current study 17 (58.6%) were also resistant to at least one of the beta-lactam antimicrobials.

Conclusion

Acquisition of blaTEM was the principal beta-lactamase resistance mechanism and mutations within QRDR of gyrA and parC were the primary mechanism for resistance to quinolones. Further study on extended spectrum beta-lactamase and quinolone resistance mechanisms in other gram negative pathogens is recommended.

Cardiac Electrical and Structural Changes During Bacterial Infection: An Instructive Model to Study Cardiac Dysfunction in Sepsis

Background

Sepsis patients with cardiac dysfunction have significantly higher mortality. Although several pathways are associated with myocardial damage in sepsis, the precise cause(s) remains unclear and treatment options are limited. This study was designed to develop a new model to investigate the early events of cardiac damage during sepsis progression.

Methods and Results

Francisella tularensis subspecies novicida (Ft.n) is a Gram‐negative intracellular pathogen causing severe sepsis syndrome in mice. BALB/c mice (N=12) were sham treated or infected with Ft.n through the intranasal route. Serial electrocardiograms were recorded at multiple time points until 96 hours. Hearts were then harvested for histology and gene expression studies. Similar to septic patients, we illustrate both cardiac electrical and structural phenotypes in our murine Ft.n infection model, including prominent R' wave formation, prolonged QRS intervals, and significant left ventricular dysfunction. Notably, in infected animals, we detected numerous microlesions in the myocardium, previously observed following nosocomial Streptococcus infection and in sepsis patients. We show that Ft.n‐mediated microlesions are attributed to cardiomyocyte apoptosis, increased immune cell infiltration, and expression of inflammatory mediators (tumor necrosis factor, interleukin [IL]‐1β, IL‐8, and superoxide dismutase 2). Finally, we identify increased expression of microRNA‐155 and rapid degradation of heat shock factor 1 following cardiac Ft.n infection as a primary cause of myocardial inflammation and apoptosis.

Conclusions

We have developed and characterized an Ft.n infection model to understand the pathogenesis of cardiac dysregulation in sepsis. Our findings illustrate novel in vivo phenotypes underlying cardiac dysfunction during Ft.n infection with significant translational impact on our understanding of sepsis pathophysiology.

Bacterial modification of LPS and resistance to antimicrobial peptides

Antimicrobial peptides (APs) are ubiquitous in nature and are thought to kill micro-organisms by affecting membrane integrity. These positively charged peptides interact with negative charges in the LPS of Gram-negative bacteria. A common mechanism of resistance to AP killing is LPS modification. These modifications include fatty acid additions, phosphoethanolamine (PEtN) addition to the core and lipid A regions, 4-amino-4-deoxy-L-arabinose (Ara4N) addition to the core and lipid A regions, acetylation of the O-antigen, and possibly hydroxylation of fatty acids. In Salmonella typhimurium, LPS modifications are induced within host tissues by the two-component regulatory systems PhoPQ and PmrAB. PmrAB activation results in AP resistance by Ara4N addition to lipid A through the activation of at least 8 genes, 7 of which are transcribed as an operon. Loss of this operon and, therefore, Ara4N LPS modification, affects S. typhimurium virulence when administered orally. Transposon mutagenesis of Proteus mirabilis also suggests that LPS modifications affect AP resistance and virulence phenotypes. Therefore, LPS modification in Gram-negative bacteria plays a significant role during infection in resistance to host antimicrobial factors, avoidance of immune system recognition, and maintenance of virulence phenotypes.

Identification of Genes Required for Secretion of the Francisella Oxidative Burst-Inhibiting Acid Phosphatase AcpA

Francisella tularensis is a Tier 1 bioterror threat and the intracellular pathogen responsible for tularemia in humans and animals. Upon entry into the host, Francisella uses multiple mechanisms to evade killing. Our previous studies have shown that after entering its primary cellular host, the macrophage, Francisella immediately suppresses the oxidative burst by secreting a series of acid phosphatases including AcpA-B-C and HapA, thereby evading the innate immune response of the macrophage and enhancing survival and further infection. However, the mechanism of acid phosphatase secretion by Francisella is still unknown. In this study, we screened for genes required for AcpA secretion in Francisella. We initially demonstrated that the known secretion systems, the putative Francisella-pathogenicity island (FPI)-encoded Type VI secretion system and the Type IV pili, do not secrete AcpA. Using random transposon mutagenesis in conjunction with ELISA, Western blotting and acid phosphatase enzymatic assays, a transposon library of 5450 mutants was screened for strains with a minimum 1.5-fold decrease in secreted (culture supernatant) AcpA, but no defect in cytosolic AcpA. Three mutants with decreased supernatant AcpA were identified. The transposon insertion sites of these mutants were revealed by direct genomic sequencing or inverse-PCR and sequencing. One of these mutants has a severe defect in AcpA secretion (at least 85% decrease) and is a predicted hypothetical inner membrane protein. Interestingly, this mutant also affected the secretion of the FPI-encoded protein, VgrG. Thus, this screen identified novel protein secretion factors involved in the subversion of host defenses.

What's on the Outside Matters: The Role of the Extracellular Polymeric Substance of Gram-negative Biofilms in Evading Host Immunity and as a Target for Therapeutic Intervention

Biofilms are organized multicellular communities encased in an extracellular polymeric substance (EPS). Biofilm-resident bacteria resist immunity and antimicrobials. The EPS provides structural stability and presents a barrier; however, a complete understanding of how EPS structure relates to biological function is lacking. This review focuses on the EPS of three Gram-negative pathogens: Pseudomonas aeruginosa, nontypeable Haemophilus influenzae, and Salmonella enterica serovar Typhi/Typhimurium. Although EPS proteins and polysaccharides are diverse, common constituents include extracellular DNA, DNABII (DNA binding and bending) proteins, pili, flagella, and outer membrane vesicles. The EPS biochemistry promotes recalcitrance and informs the design of therapies to reduce or eliminate biofilm burden.

Fecal prevalence, serotype distribution and antimicrobial resistance of Salmonellae in dairy cattle in central Ethiopia

Background

Salmonellae are major worldwide zoonotic pathogens infecting a wide range of vertebrate species including humans. Consumption of contaminated dairy products and contact with dairy cattle represent a common source of non-typhoidal Salmonella infection in humans. Despite a large number of small-scale dairy farms in Addis Ababa and its surrounding districts, little is known about the status of Salmonella in these farms.

Results

Salmonella was recovered from the feces of at least one animal in 7.6 % (10/132) of the dairy farms. Out of 1203 fecal samples examined, 30 were positive for Salmonella resulting in a weighted animal level prevalence of 2.3 %. Detection of diarrhea in an animal and in a farm was significantly associated with animal level (p = 0.012) and herd level (p < 0.001) prevalence of Salmonella. Animal level prevalence of Salmonella was significantly associated with age (p = 0.023) and study location; it was highest among those under 6 months of age and in farms from Adaa district and Addis Ababa (p < 0.001). Nine different serotypes were identified using standard serological agglutination tests. The most frequently recovered serotypes were Salmonella Typhimurium (23.3 %), S. Saintpaul (20 %), S. Kentucky (16.7 %) and S. Virchow (16.7 %). All isolates were resistant or intermediately resistant to at least one of the 18 drugs tested. Twenty-six (86.7 %), 19 (63.3 %), 18 (60 %), 16 (53.3 %) of the isolates were resistant to streptomycin, nitrofurantoin, sulfisoxazole and tetracycline , respectively. Resistance to 2 drugs was detected in 27 (90 %) of the isolates. Resistance to 3 or more drugs was detected in 21 (70 %) of the isolates, while resistance to 7 or more drugs was detected in 11 (36.7 %) of the isolates. The rate of occurrence of multi-drug resistance (MDR) in Salmonella strains isolated from dairy farms in Addis Ababa was significantly higher than those isolated from farms outside of Addis Ababa (p = 0.009). MDR was more common in S. Kentucky, S. Virchow and S. Saintpaul.

Conclusion

Isolation of Salmonella serotypes commonly known for causing human salmonellosis that are associated with an MDR phenotype in dairy farms in close proximity with human population is a major public health concern. These findings imply the need for a strict pathogen reduction strategy.

Non-typhoidal Salmonella serotypes, antimicrobial resistance and co-infection with parasites among patients with diarrhea and other gastrointestinal complaints in Addis Ababa, Ethiopia

BACKGROUND

Non-typhoidal Salmonella (NTS) is an important public health problem worldwide. Consumption of animal-derived food products and direct and/or indirect contact with animals are the major routes of acquiring infection with NTS. Published information, particularly on the serotype distribution of NTS among human patients with gastroenteritis and associated risk factors, is scarce in Ethiopia. This study investigated the prevalence, risk factors, serotype distribution and antimicrobial susceptibility of Salmonella species among diarrheic out-patients attending health centers in Addis Ababa and patients with various gastrointestinal complaints at Tikur Anbessa Specialized Hospital (TASH).

METHODS

Stool samples were cultured for Salmonella species according to the WHO Global Foodborne Infections Network laboratory protocol. Salmonella serotyping was conducted using slide agglutination and microplate agglutination techniques. Antibiotic susceptibility testing was performed using the disk diffusion method according to Clinical and Laboratory Standards Institute guidelines.

RESULTS

A total of 59 (6.2 %) stool samples, out of 957 were culture positive for Salmonella species. Fifty-five (7.2 %) of 765 diarrheic patients from health centers and 4 (2.1 %) of 192 patients from TASH were culture positive for Salmonella species. Multivariable logistic regression analysis after adjusting for all other variables revealed statistically significant association of Salmonella infection with consumption of raw vegetables (OR = 1.91, 95 % CI = 1.29-2.83, χ(2) = 4.74, p = 0.025) and symptom of watery diarrhea (OR = 3.3, 95 % CI = 1.23-8.88, χ(2) = 10.54, p = 0.005). Eleven serotypes were detected, and the most prominent were S. Typhimurium (37.3 %), S. Virchow (34 %), and S. Kottbus (10.2 %). Other serotypes were S. Miami, S. Kentucky, S. Newport, S. Enteritidis, S. Braenderup, S. Saintpaul, S. Concord and S. V:ROUGH-O. Resistance to three or more antimicrobials was detected in 27 (40.3 %) of the isolates. Resistance to five or more antimicrobials was detected in 17 (25.4 %). Resistance to individual antimicrobials was found at varying proportions: streptomycin (50; 74.6 %), nitrofurantoin (27; 40.3 %), sulfisoxazole (26; 38.8 %), kanamycin (23; 34.3 %), cephalothin (12; 17.9 %), and ampicillin (11; 16.4 %) respectively. Two S. Kentucky, one S. Typhimurium and one S. Concord isolates were multi-drug resistant to more than 10 antimicrobials.

CONCLUSIONS

The study demonstrated significant association of Salmonella infection with consumption of raw vegetables. There was no significant association of Salmonella infection with co-occurring parasites. The study also showed the dominance of S. Typhimurium and S. Virchow in primary health care units. Overall, prevalence of MDR was low compared to previous studies. Although their proportion was low, S. Kentucky and S. Concord demonstrated wider spectrum of MDR. Continuous monitoring of circulating serotypes, antimicrobial resistance profile and characterization on molecular resistance determinants is essential for proper treatment of patients and for identifying potential environmental origins of antimicrobial resistance.

The O-Antigen Capsule of Salmonella enterica Serovar Typhimurium Facilitates Serum Resistance and Surface Expression of FliC

Group IV polysaccharide capsules are common in enteric bacteria and have more recently been described in nontyphoidal Salmonella species. Such capsules are known as O-antigen (O-Ag) capsules, due to their high degree of similarity to the O-Ag of the lipopolysaccharide (LPSO-Ag). Capsular polysaccharides are known virulence factors of many bacterial pathogens, facilitating evasion of immune recognition and systemic dissemination within the host. Previous studies on the O-Ag capsule of salmonellae have focused primarily on its role in bacterial surface attachment and chronic infection; however, the potential effects of the O-Ag capsule on acute pathogenesis have yet to be investigated. While much of the in vivo innate immune resistance of Salmonella enterica serovar Typhimurium is attributed to the high-molecular-weight LPS, we hypothesized that the O-Ag capsule may enhance this resistance by diminishing surface expression of pathogen-associated molecular patterns, such as flagella, and increasing resistance to host immune molecules. To test this hypothesis, O-Ag capsule-deficient mutants were constructed, and the loss of O-Ag capsular surface expression was confirmed through microscopy and immunoblotting. Loss of O-Ag capsule production did not alter bacterial growth or production of LPS. Western blot analysis and confocal microscopy revealed that O-Ag capsule-deficient mutants demonstrate reduced resistance to killing by human serum. Furthermore, O-Ag capsule-deficient mutants produced exclusively phase I flagellin (FliC). Although O-Ag capsule-deficient mutants did not exhibit reduced virulence in a murine model of acute infection, in vitro results indicate that the O-Ag capsule may function to modify the antigenic nature of the bacterial surface, warranting additional investigation of a potential role of the structure in pathogenesis.

Acetalated dextran encapsulated AR-12 as a host-directed therapy to control Salmonella infection

AR-12 has been evaluated in clinical trials as an anti-cancer agent but also has demonstrated host-directed, broad-spectrum clearance of bacteria. We have previously shown that AR-12 has activity in vitro against Salmonella enterica serovar Typhimurium and Francisella species by inducing autophagy and other host immune pathways. AR-12 treatment of S. Typhimurium-infected mice resulted in a 10-fold reduction in bacterial load in the liver and spleen and an increased survival time. However, AR-12 treatment did not protect mice from death, likely due poor formulation. In the current study, AR-12 was encapsulated in a microparticulate carrier formulated from the novel degradable biopolymer acetalated dextran (Ace-DEX) and subsequently evaluated for its activity in human monocyte-derived macrophages (hMDMs). Our results show that hMDMs efficiently internalized Ace-DEX microparticles (MPs), and that encapsulation significantly reduced host cell cytotoxicity compared to unencapsulated AR-12. Efficient macrophage internalization of AR-12 loaded MPs (AR-12/MPs) was further demonstrated by autophagosome formation that was comparable to free AR-12 and resulted in enhanced clearance of intracellular Salmonella. Taken together, these studies provide support that Ace-DEX encapsulated AR-12 may be a promising new therapeutic agent to control intracellular bacterial pathogens of macrophages by targeting delivery and reducing drug toxicity.

Salmonella Typhimurium strain ATCC14028 requires H2-hydrogenases for growth in the gut, but not at systemic sites

Salmonella enterica is a common cause of diarrhea. For eliciting disease, the pathogen has to colonize the gut lumen, a site colonized by the microbiota. This process/initial stage is incompletely understood. Recent work established that one particular strain, Salmonella enterica subspecies 1 serovar Typhimurium strain SL1344, employs the hyb H₂-hydrogenase for consuming microbiota-derived H₂ to support gut luminal pathogen growth: Protons from the H₂-splitting reaction contribute to the proton gradient across the outer bacterial membrane which can be harvested for ATP production or for import of carbon sources. However, it remained unclear, if other Salmonella strains would use the same strategy. In particular, earlier work had left unanswered if strain ATCC14028 might use H₂ for growth at systemic sites. To clarify the role of the hydrogenases, it seems important to establish if H₂ is used at systemic sites or in the gut and if Salmonella strains may differ with respect to the host sites where they require H₂ in vivo. In order to resolve this, we constructed a strain lacking all three H₂-hydrogenases of ATCC14028 (14028^hyd3) and performed competitive infection experiments. Upon intragastric inoculation, 14028^hyd3 was present at 100-fold lower numbers than 14028^WT in the stool and at systemic sites. In contrast, i.v. inoculation led to equivalent systemic loads of 14028^hyd3 and the wild type strain. However, the pathogen population spreading to the gut lumen featured again up to 100-fold attenuation of 14028^hyd3. Therefore, ATCC14028 requires H₂-hydrogenases for growth in the gut lumen and not at systemic sites. This extends previous work on ATCC14028 and supports the notion that H₂-utilization might be a general feature of S. Typhimurium gut colonization.

In vitro modeling of gallbladder-associated Salmonella spp. colonization

The host-pathogen interactions occurring in the gallbladder during Salmonella Typhi colonization contribute to typhoid fever pathogenesis during the acute and chronic stages of disease. The gallbladder is the primary reservoir during chronic typhoid carriage. In this organ, Salmonella encounters host-barriers including bile, immunoglobulins, and mucus. However, the bacterium possesses mechanisms to resist and persist in this environment, in part by its ability to attach to and invade into the gallbladder epithelium. Such persistence in the gallbladder epithelium contributes to chronic carriage. In addition, patients harboring gallstones in their gallbladders have increased risk of becoming carriers because these abnormalities serve as a substrate for Salmonella biofilm formation. Our laboratory has studied the Salmonella interactions in this specific environment by developing in vitro methods that closely mimic the gallbladder and gallstones niches. These methods are reproducible and provide a platform for future studies of acute and chronic bacterial infections in the gallbladder.

Salmonella chronic carriage: epidemiology, diagnosis, and gallbladder persistence

Typhoid (enteric fever) remains a major cause of morbidity and mortality worldwide, causing over 21 million new infections annually, with the majority of deaths occurring in young children. Because typhoid fever-causing Salmonella have no known environmental reservoir, the chronic, asymptomatic carrier state is thought to be a key feature of continued maintenance of the bacterium within human populations. Despite the importance of this disease to public health, our understanding of the molecular mechanisms that catalyze carriage, as well as our ability to reliably identify and treat the Salmonella carrier state, have only recently begun to advance.

Association of multicellular behaviour and drug resistance in Salmonella enterica serovars isolated from animals and humans in Ethiopia

AIMS

To determine the association between multicellular behaviour, integron status and antibiotic resistance among 87 Ethiopian Salmonella enterica isolates of animal and human origin.

METHODS AND RESULTS

Isolates were characterized for their biofilm forming ability, antimicrobial susceptibility and the presence and characteristics of a class 1 integron and Salmonella genomic island 1 (SGI1). The majority of isolates grown at environmental temperatures (20°C) exhibited robust biofilm formation (72·4%) and displayed RDAR colony morphology on Congo red agar plates. The presence of a class 1 integron correlated with the extent of drug resistance and ability to exhibit multicellular behaviour.

CONCLUSIONS

Although cellulose production and RDAR morphology correlated with increased multicellular behaviour, neither was required for biofilm formation. Contrary to previous reports, colony morphology was generally consistent within a serovar. No integrons were detected in isolates deficient for multicellular behaviour, indicating a potential role of bacterial community formation in transfer of genetic elements among environmental isolates.

SIGNIFICANCE AND IMPACT OF STUDY

Infection by Salm. enterica is a major public health problem worldwide. The dominance of multidrug resistance and multicellular behaviour in Salmonella isolates of Ethiopian origin highlights a need for integrated surveillance and further detailed phenotypic and molecular studies of isolates from this region.

Visualization of extracellular matrix components within sectioned Salmonella biofilms on the surface of human gallstones

Chronic carriage of Salmonella Typhi is mediated primarily through the formation of bacterial biofilms on the surface of cholesterol gallstones. Biofilms, by definition, involve the formation of a bacterial community encased within a protective macromolecular matrix. Previous work has demonstrated the composition of the biofilm matrix to be complex and highly variable in response to altered environmental conditions. Although known to play an important role in bacterial persistence in a variety of contexts, the Salmonella biofilm matrix remains largely uncharacterized under physiological conditions. Initial attempts to study matrix components and architecture of the biofilm matrix on gallstone surfaces were hindered by the auto-fluorescence of cholesterol. In this work we describe a method for sectioning and direct visualization of extracellular matrix components of the Salmonella biofilm on the surface of human cholesterol gallstones and provide a description of the major matrix components observed therein. Confocal micrographs revealed robust biofilm formation, characterized by abundant but highly heterogeneous expression of polysaccharides such as LPS, Vi and O-antigen capsule. CsgA was not observed in the biofilm matrix and flagellar expression was tightly restricted to the biofilm-cholesterol interface. Images also revealed the presence of preexisting Enterobacteriaceae encased within the structure of the gallstone. These results demonstrate the use and feasibility of this method while highlighting the importance of studying the native architecture of the gallstone biofilm. A better understanding of the contribution of individual matrix components to the overall biofilm structure will facilitate the development of more effective and specific methods to disrupt these bacterial communities.

Histopathological analysis of Salmonella chronic carriage in the mouse hepatopancreatobiliary system

Salmonella Typhi asymptomatic chronic carriage represents a challenge for the diagnosis and prevention of typhoid fever in endemic areas. Such carriers are thought to be reservoirs for further spread of the disease. Gallbladder carriage has been demonstrated to be mediated by biofilm formation on gallstones and by intracellular persistence in the gallbladder epithelium of mice. In addition, both gallstones and chronic carriage have been associated with chronic inflammation and the development of gallbladder carcinoma. However, the pathogenic relationship between typhoid carriage and the development of pre-malignant and/or malignant lesions in the hepatopancreatobiliary system as well as the host-pathogen interactions occurring during chronic carriage remains unclear. In this study, we monitored the histopathological features of chronic carriage up to 1 year post-infection. Chronic cholecystitis and hepatitis ranging from mild to severe were present in infected mice regardless of the presence of gallstones. Biliary epithelial hyperplasia was observed more commonly in the gallbladder of mice with gallstones (uninfected or infected). However, pre-malignant lesions, atypical hyperplasia and metaplasia of the gallbladder and exocrine pancreas, respectively, were only associated with chronic Salmonella carriage. This study has implications regarding the role of Salmonella chronic infection and inflammation in the development of pre-malignant lesions in the epithelium of the gallbladder and pancreas that could lead to oncogenesis.

Delivery of host cell-directed therapeutics for intracellular pathogen clearance

Intracellular pathogens present a major health risk because of their innate ability to evade clearance. Their location within host cells and ability to react to the host environment by mutation or transcriptional changes often enables survival mechanisms to resist standard therapies. Host-directed drugs do not target the pathogen, minimizing the potential development of drug resistance; however, they can be difficult to deliver efficiently to intracellular sites. Vehicle delivery of host-mediated response drugs not only improves drug distribution and toxicity profiles, but can reduce the total amount of drug necessary to clear infection. In this article, we will review some host-directed drugs and current drug delivery techniques that can be used to efficiently clear intracellular infections.

Identification of immunogenic Salmonella enterica serotype Typhi antigens expressed in chronic biliary carriers of S. Typhi in Kathmandu, Nepal

Background

Salmonella enterica serotype Typhi can colonize and persist in the biliary tract of infected individuals, resulting in a state of asymptomatic chronic carriage. Chronic carriers may act as persistent reservoirs of infection within a community and may introduce infection to susceptible individuals and new communities. Little is known about the interaction between the host and pathogen in the biliary tract of chronic carriers, and there is currently no reliable diagnostic assay to identify asymptomatic S. Typhi carriage.

Methodology/Principal Findings

To study host-pathogen interactions in the biliary tract during S. Typhi carriage, we applied an immunoscreening technique called in vivo-induced antigen technology (IVIAT), to identify potential biomarkers unique to carriers. IVIAT identifies humorally immunogenic bacterial antigens expressed uniquely in the in vivo environment, and we hypothesized that S. Typhi surviving in the biliary tract of humans may express a distinct antigenic profile. Thirteen S. Typhi antigens that were immunoreactive in carriers, but not in healthy individuals from a typhoid endemic area, were identified. The identified antigens included a number of putative membrane proteins, lipoproteins, and hemolysin-related proteins. YncE (STY1479), an uncharacterized protein with an ATP-binding motif, gave prominent responses in our screen. The response to YncE in patients whose biliary tract contained S. Typhi was compared to responses in patients whose biliary tract did not contain S. Typhi, patients with acute typhoid fever, and healthy controls residing in a typhoid endemic area. Seven of 10 (70%) chronic carriers, 0 of 8 bile culture-negative controls (0%), 0 of 8 healthy Bangladeshis (0%), and 1 of 8 (12.5%) Bangladeshis with acute typhoid fever had detectable anti-YncE IgG in blood. IgA responses were also present.

Conclusions/Significance

Further evaluation of YncE and other antigens identified by IVIAT could lead to the development of improved diagnostic assays to identify asymptomatic S. Typhi carriers.

Salmonella enterica serotype Typhi is the cause of typhoid fever and infects over 21 million individuals and causes 200,000 deaths each year. With adequate treatment, most patients recover from their acute stage of illness and clear infection. However, a small percentage of S. Typhi infected individuals develop a chronic but asymptomatic infection in the biliary tract that can persist for decades. Since S. Typhi is a human-restricted pathogen, chronic carriers may act as reservoirs of infection. Correctly identifying and treating asymptomatic chronic carriers could be critical for ultimate control of typhoid fever. Using an immunoscreening technique called in vivo-induced antigen technology (IVIAT), we have identified potential biomarkers unique to S. Typhi chronic carriers. Further evaluation of these antigens could lead to the development of improved diagnostic assays to detect asymptomatic S. Typhi carriers in typhoid endemic zones, and to an improved understanding of the pathogenesis of S. Typhi in the chronic carrier state.

Type A Francisella tularensis acid phosphatases contribute to pathogenesis

Different Francisella spp. produce five or six predicted acid phosphatases (AcpA, AcpB, AcpC, AcpD, HapA and HapB). The genes encoding the histidine acid phosphatases (hapA, hapB) and acpD of F. tularensis subsp. Schu S4 strain are truncated or disrupted. However, deletion of HapA (FTT1064) in F. tularensis Schu S4 resulted in a 33% reduction in acid phosphatase activity and loss of the four functional acid phosphatases in F. tularensis Schu S4 (ΔABCH) resulted in a>99% reduction in acid phosphatase activity compared to the wild type strain. All single, double and triple mutants tested, demonstrated a moderate decrease in mouse virulence and survival and growth within human and murine phagocytes, whereas the ΔABCH mutant showed >3.5-fold decrease in intramacrophage survival and 100% attenuation of virulence in mouse. While the Schu S4 ΔABCH strain was attenuated in the mouse model, it showed only limited protection against wild type challenge. F. tularensis Schu S4 failed to stimulate reactive oxygen species production in phagocytes, whereas infection by the ΔABCH strain stimulated 5- and 56-fold increase in reactive oxygen species production in neutrophils and human monocyte-derived macrophages, respectively. The ΔABCH mutant but not the wild type strain strongly co-localized with p47^phox and replicated in macrophages isolated from p47^phox knockout mice. Thus, F. tularensis Schu S4 acid phosphatases, including the truncated HapA, play a major role in intramacrophage survival and virulence of this human pathogen.

Cationic antimicrobial peptides serve as activation signals for the Salmonella Typhimurium PhoPQ and PmrAB regulons in vitro and in vivo

Salmonella enterica serovar Typhimurium uses two-component regulatory systems (TCRSs) to respond to environmental stimuli. Upon infection, the TCRSs PhoP-PhoQ (PhoPQ) and PmrA-PmrB (PmrAB) are activated by environmental signals detected in the lumen of the intestine and within host cells. TCRS-mediated gene expression leads to upregulation of genes involved in lipopolysaccharide (LPS) modification and cationic antimicrobial peptide (CAMP) resistance. This research expands on previous studies which have shown that CAMPs can activate Salmonella TCRSs in vitro. The focus of this work was to determine if CAMPs can act as environmental signals for PhoPQ- and PmrAB-mediated gene expression in vitro, during infection of macrophages and in a mouse model of infection. Monitoring of PhoPQ and PmrAB activation using recombinase-based in vivo expression technology (RIVET), alkaline phosphtase and β-galactosidase reporter fusion constructs demonstrated that S. Typhimurium PhoQ can sense CAMPs in vitro. In mouse macrophages, the cathelecidin CRAMP does not activate the PhoPQ regulon. Acidification of the Salmonella-containing vacuole activates PhoP- and PmrA-regulated loci but blocking acidification still does not reveal a role for CRAMP in TCRS activation in mouse macrophages. However, assays performed in susceptible wild type (WT), CRAMP knockout (KO), and matrilysin (a metalloproteinase necessary for activating murine α-defensins) KO mice suggest CRAMP, but not α-defensins, serve as a putative direct TCRS activation signal in the mouse intestine. These studies provide a better understanding of the in vivo environments that result in activation of these virulence-associated TCRSs.

Subversion of innate and adaptive immune activation induced by structurally modified lipopolysaccharide from Salmonella typhimurium

Salmonella are successful pathogens that infect millions of people every year. During infection, Salmonella typhimurium changes the structure of its lipopolysaccharide (LPS) in response to the host environment, rendering bacteria resistant to cationic peptide lysis in vitro. However, the role of these structural changes in LPS as in vivo virulence factors and their effects on immune responses and the generation of immunity are largely unknown. We report that modified LPS are less efficient than wild-type LPS at inducing pro-inflammatory responses. The impact of this LPS-mediated subversion of innate immune responses was demonstrated by increased mortality in mice infected with a non-lethal dose of an attenuated S. typhimurium strain mixed with the modified LPS moieties. Up-regulation of co-stimulatory molecules on antigen-presenting cells and CD4(+) T-cell activation were affected by these modified LPS. Strains of S. typhimurium carrying structurally modified LPS are markedly less efficient at inducing specific antibody responses. Immunization with modified LPS moiety preparations combined with experimental antigens, induced an impaired Toll-like receptor 4-mediated adjuvant effect. Strains of S. typhimurium carrying structurally modified LPS are markedly less efficient at inducing immunity against challenge with virulent S. typhimurium. Hence, changes in S. typhimurium LPS structure impact not only on innate immune responses but also on both humoral and cellular adaptive immune responses.

Interaction of Salmonella spp. with the Intestinal Microbiota

Salmonella spp. are major cause of human morbidity and mortality worldwide. Upon entry into the human host, Salmonella spp. must overcome the resistance to colonization mediated by the gut microbiota and the innate immune system. They successfully accomplish this by inducing inflammation and mechanisms of innate immune defense. Many models have been developed to study Salmonella spp. interaction with the microbiota that have helped to identify factors necessary to overcome colonization resistance and to mediate disease. Here we review the current state of studies into this important pathogen/microbiota/host interaction in the mammalian gastrointestinal tract.

Regulation of francisella tularensis virulence

Francisella tularensis is one of the most virulent bacteria known and a Centers for Disease Control and Prevention Category A select agent. It is able to infect a variety of animals and insects and can persist in the environment, thus Francisella spp. must be able to survive in diverse environmental niches. However, F. tularensis has a surprising dearth of sensory and regulatory factors. Recent advancements in the field have identified new functions of encoded transcription factors and greatly expanded our understanding of virulence gene regulation. Here we review the current knowledge of environmental adaptation by F. tularensis, its transcriptional regulators and their relationship to animal virulence.

Francisella tularensis blue-gray phase variation involves structural modifications of lipopolysaccharide o-antigen, core and lipid a and affects intramacrophage survival and vaccine efficacy

Francisella tularensis is a CDC Category A biological agent and a potential bioterrorist threat. There is no licensed vaccine against tularemia in the United States. A long-standing issue with potential Francisella vaccines is strain phase variation to a gray form that lacks protective capability in animal models. Comparisons of the parental strain (LVS) and a gray variant (LVSG) have identified lipopolysaccharide (LPS) alterations as a primary change. The LPS of the F. tularensis variant strain gains reactivity to F. novicida anti-LPS antibodies, suggesting structural alterations to the O-antigen. However, biochemical and structural analysis of the F. tularensis LVSG and LVS LPS demonstrated that LVSG has less O-antigen but no major O-antigen structural alterations. Additionally, LVSG possesses structural differences in both the core and lipid A regions, the latter being decreased galactosamine modification. Recent work has identified two genes important in adding galactosamine (flmF2 and flmK) to the lipid A. Quantitative real-time PCR showed reduced transcripts of both of these genes in the gray variant when compared to LVS. Loss of flmF2 or flmK caused less frequent phase conversion but did not alter intramacrophage survival or colony morphology. The LVSG strain demonstrated an intramacrophage survival defect in human and rat but not mouse macrophages. Consistent with this result, the LVSG variant demonstrated little change in LD₅₀ in the mouse model of infection. Furthermore, the LVSG strain lacks the protective capacity of F. tularensis LVS against virulent Type A challenge. These data suggest that the LPS of the F. tularensis LVSG phase variant is dramatically altered. Understanding the mechanism of blue to gray phase variation may lead to a way to inhibit this variation, thus making future F. tularensis vaccines more stable and efficacious.