Extracellular deoxyribonuclease made by group A Streptococcus assists pathogenesis by enhancing evasion of the innate immune response

A Conserved Endonuclease From Rust Fungi Suppresses Plant Extracellular DNA-Triggered Immunity

Nuclease 1 (NUC1) is a highly conserved nonspecific endonuclease present in vertebrates, fungi, and a few plant species. While the involvement of yeast NUC1p in apoptotic cell death independent of metacaspase or apoptosis-inducing factors is documented, its function in other fungi, particularly pathogenic ones, remains elusive. In this study, we identified and characterised the homologue of yeast NUC1p, termed PstNUC1, in Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. PstNUC1 was induced during infection and was secreted to the extracellular space of the host. Silencing of PstNUC1 significantly attenuated the virulence of Pst, suggesting its critical role in pathogenicity. Exogenous treatment of PstNUC1 diminished the extracellular DNA (exDNA)-triggered plant immune response, including cell death, oxygen peroxide production, and upregulation of Pathogenesis-related genes. Notably, overexpression of wild-type PstNUC1, but not a signal peptide-deficient mutant (PstNUC1ΔSP), in wheat compromised exDNA-triggered immunity, resulting in enhanced susceptibility to Pst infection. These finding collectively highlight the contribution of PstNUC1 to virulence through degradation of exDNA, thereby dampening the exDNA-induced plant immune response.

Streptococcus intermedius: an underestimated pathogen in brain infection?

Streptococcus intermedius is an oral commensal organism belonging to the Streptococcus anginosus group (SAG). S. intermedius causes periodontitis as well as invasive, pyogenic infection of the central nervous system, pleural space or liver. Compared with other SAG organisms, S. intermedius has a higher mortality as well as a predilection for intracranial infection, suggesting it is likely to possess virulence factors that mediate specific interactions with the host resulting in bacteria reaching the brain. The mechanisms involved are not well described. Intracranial suppuration (ICS) due to S. intermedius infection can manifest as an abscess within the brain parenchyma, or a collection of pus (empyema) in the sub- or extra-dural space. These infections necessitate neurosurgery and prolonged antibiotic treatment and are associated with a considerable burden of morbidity and mortality. The incidence of ICS is increasing in several settings, with SAG species accounting for an increasing proportion of cases. There is a paucity of published literature regarding S. intermedius pathogenesis as well as few published genomes, hampering molecular epidemiological research. This perspective evaluates what is known about the clinical features and pathogenesis of ICS due to S. intermedius and explores hypothetical explanations why the incidence of these infections may be increasing.

The burden of group A Streptococcus (GAS) infections: The challenge continues in the twenty-first century

Streptococcus pyogenes is a Gram-positive bacterium, also known as Group A Streptococcus (GAS), that has become a significant threat to the healthcare system, infecting more than 18 million people and resulting in more than 500,000 deaths annually worldwide. GAS infection rates decreased gradually during the 20th century in Western countries, largely due to improved living conditions and access to antibiotics. However, post-COVID-19, the situation has led to a steep increase in GAS infection rates in Europe, the United States, Australia, and New Zealand, which triggers a global concern. GAS infections are normally moderate, with symptoms of fever, pharyngitis, and pyoderma; nevertheless, if left untreated or with continued exposure to GAS or with recurring infections it can result in fatal outcomes. GAS produces a variety of virulence factors and exotoxins that can lead to deadly infections such as necrotizing fasciitis, impetigo, cellulitis, pneumonia, empyema, streptococcal toxic shock syndrome, bacteremia, and puerperal sepsis. In addition, post-immune mediated disorders such as post-streptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease contribute to extremely high death rates in developing nations. Despite substantial research on GAS infections, it is still unclear what molecular pathways are responsible for their emergence and how to best manage them. This review thus provides insights into the most recent research on the pathogenesis, virulence, resistance, and host interaction mechanisms of GAS, as well as novel management options to assist scientific communities in combating GAS infections.

Streptococcus anginosus orchestrates antibacterial potential of NETs facilitating survival of accompanying pathogens

Streptococcus anginosus is considered an emerging opportunistic pathogen causing life-threatening infections, including abscesses and empyema. Noticeably, clinical data revealed that S. anginosus also constitutes an important component of polymicrobial infections. Here, we showed for the first time that S. anginosus inactivates the antibacterial potential of neutrophil extracellular traps (NETs). The process is determined by a cell wall-anchored nuclease referred to as SanA, which high expression dominates in clinical strains isolated from severe infections. Nuclease activity protects S. anginosus against the antibacterial activity of NETs, supporting at the same time the survival of coexisting highly pathogenic species of Enterobacteriales. Obtained data suggest that SanA nuclease should be recognized as a critical S. anginosus virulence factor determining severe monospecies purulent infections but also shielding other pathogens promoting the development of polymicrobial infections.

Nosocomial Transmission of Necrotizing Fasciitis: A Molecular Characterization of Group A Streptococcal DNases in Clinical Virulence

Streptococcus pyogenes, or Group A Streptococcus (GAS), is responsible for over 500,000 deaths per year. Approximately 15% of these deaths are caused by necrotizing soft-tissue infections. In 2008, we isolated an M5 GAS, named the LO1 strain, responsible for the nosocomial transmission of necrotizing fasciitis between a baby and a nurse in Belgium. To understand this unusual transmission route, the LO1 strain was sequenced. A comparison of the LO1 genome and transcriptome with the reference M5 Manfredo strain was conducted. We found that the major differences were the presence of an additional DNase and a Tn916-like transposon in the LO1 and other invasive M5 genomes. RNA-seq analysis showed that genes present on the transposon were barely expressed. In contrast, the DNases presented different expression profiles depending on the tested conditions. We generated knock-out mutants in the LO1 background and characterized their virulence phenotype. We also determined their nuclease activity on different substrates. We found that DNases are dispensable for biofilm formation and adhesion to both keratinocytes and pharyngeal cells. Three of these were found to be essential for blood survival; Spd4 and Sdn are implicated in phagocytosis resistance, and Spd1 is responsible for neutrophil extracellular trap (NET) degradation.

Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes

SUMMARYStreptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized cause of disease in humans. Disease manifestations range from non-invasive superficial skin and soft tissue infections to life-threatening streptococcal toxic shock syndrome and necrotizing fasciitis. Invasive disease is usually associated with co-morbidities, immunosuppression, and advancing age. The crude incidence of invasive disease approaches that of the closely related pathogen, Streptococcus pyogenes. Genomic epidemiology using whole-genome sequencing has revealed important insights into global SDSE population dynamics including emerging lineages and spread of anti-microbial resistance. It has also complemented observations of overlapping pathobiology between SDSE and S. pyogenes, including shared virulence factors and mobile gene content, potentially underlying shared pathogen phenotypes. This review provides an overview of the clinical and genomic epidemiology, disease manifestations, treatment, and virulence determinants of human infections with SDSE with a particular focus on its overlap with S. pyogenes. In doing so, we highlight the importance of understanding the overlap of SDSE and S. pyogenes to inform surveillance and disease control strategies.

The continuing need for dornase alfa for extracellular airway DNA hydrolysis in the era of CFTR modulators

INTRODUCTION

The availability of cystic fibrosis transmembrane conductance regulator (CFTR) modulators opens the possibility of discontinuing some chronic pulmonary therapies to decrease cystic fibrosis (CF) treatment burden. However, CFTR modulators may not adequately address neutrophilic inflammation, which contributes to a self-perpetual cycle of viscous CF sputum, airway obstruction, inflammation, and lung function decline.

AREAS COVERED

This review discusses the emerging role of neutrophil extracellular traps in CF and its role in CF sputum viscosity, airway obstruction, and inflammation, based on a literature search of PubMed (1990-present). We summarize clinical trials and real-world studies that support the efficacy of dornase alfa (Pulmozyme) in improving lung function and reducing pulmonary exacerbation in people with CF (PwCF), and we discuss the potential role of dornase alfa in reducing airway inflammation. We also examine the findings of short-term trials evaluating the discontinuation of mucoactive therapy in PwCF receiving CFTR modulators.

EXPERT OPINION

Long-term studies are needed to assess the impact of discontinuing mucoactive therapy in PwCF who are clinically stable while receiving CFTR modulatory therapy. Treatment decisions should take into account the severity of underlying lung disease. People with advanced CF will likely require ongoing mucoactive therapy.

Dying for a cause: The pathogenic manipulation of cell death and efferocytic pathways

Cell death is a natural consequence of infection. However, although the induction of cell death was solely thought to benefit the pathogen, compelling data now show that the activation of cell death pathways serves as a nuanced antimicrobial strategy that couples pathogen elimination with the generation of inflammatory cytokines and the priming of innate and adaptive cellular immunity. Following cell death, the phagocytic uptake of the infected dead cell by antigen-presenting cells and the subsequent lysosomal fusion of the apoptotic body containing the pathogen serve as an important antimicrobial mechanism that furthers the development of downstream adaptive immune responses. Despite the complexity of regulated cell death pathways, pathogens are highly adept at evading them. Here, we provide an overview of the remarkable diversity of cell death and efferocytic pathways and discuss illustrative examples of virulence strategies employed by pathogens, including oral pathogens, to counter their activation and persist within the host.

Molecular Aggregation Strategy for Inhibiting DNases

This study highlights the novel potential of molecular aggregates as inhibitors of a disease-related protein. Enzyme inhibitors have been studied and developed as molecularly targeted drugs and have been applied for cancer, autoimmune diseases, and infections. In many cases, enzyme inhibitors that are used for therapeutic applications interact directly with enzymes in a molecule-to-molecule manner. We found that the aggregates of a small compound, Mn007, inhibited bovine pancreatic DNase I. Once Mn007 molecules formed aggregates, they exhibited inhibitory effects specific to DNases that require divalent metal ions. A DNase secreted by Streptococcus pyogenes causes streptococcal toxic shock syndrome (STSS). STSS is a severe infectious disease with a fatality rate exceeding 30% in patients, even in this century. S. pyogenes disrupts the human barrier system against microbial infections through the secreted DNase. Until now, the discovery/development of a DNase inhibitor has been challenging. Mn007 aggregates were found to inhibit the DNase secreted by S. pyogenes, which led to the successful suppression of S. pyogenes growth in human whole blood. To date, molecular aggregation has been outside the scope of drug discovery. The present study suggests that molecular aggregation is a vast area to be explored for drug discovery and development because aggregates of small-molecule compounds can inhibit disease-related enzymes.

Bacterial cholesterol-dependent cytolysins and their interaction with the human immune response

PURPOSE OF REVIEW

Many cholesterol-dependent cytolysin (CDC)-producing pathogens pose a significant threat to human health. Herein, we review the pore-dependent and -independent properties CDCs possess to assist pathogens in evading the host immune response.

RECENT FINDINGS

Within the last 5 years, exciting new research suggests CDCs can act to inhibit important immune functions, disrupt critical cell signaling pathways, and have tissue-specific effects. Additionally, recent studies have identified a key region of CDCs that generates robust immunity, providing resources for the development of CDC-based vaccines.

SUMMARY

This review provides new information on how CDCs alter host immune responses to aid bacteria in pathogenesis. These studies can assist in the design of more efficient vaccines and therapeutics against CDCs that will enhance the immune response to CDC-producing pathogens while mitigating the dampening effects CDCs have on the host immune response.

Inter-species gene flow drives ongoing evolution of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of human infection with invasive disease incidence and clinical manifestations comparable to the closely related species, Streptococcus pyogenes. Through systematic genomic analyses of 501 disseminated SDSE strains, we demonstrate extensive overlap between the genomes of SDSE and S. pyogenes. More than 75% of core genes are shared between the two species with one third demonstrating evidence of cross-species recombination. Twenty-five percent of mobile genetic element (MGE) clusters and 16 of 55 SDSE MGE insertion regions were shared across species. Assessing potential cross-protection from leading S. pyogenes vaccine candidates on SDSE, 12/34 preclinical vaccine antigen genes were shown to be present in >99% of isolates of both species. Relevant to possible vaccine evasion, six vaccine candidate genes demonstrated evidence of inter-species recombination. These findings demonstrate previously unappreciated levels of genomic overlap between these closely related pathogens with implications for streptococcal pathobiology, disease surveillance and prevention.

Impact of bronchoalveolar lavage from influenza A virus diseased pigs on neutrophil functions and growth of co-infecting pathogenic bacteria

Introduction

Influenza A viruses (IAVs) infect the respiratory tract of mainly humans, poultry, and pigs. Co-infections with pathogenic lung bacteria are a common event and contribute to the severity of disease progression. Neutrophils are a major cell type of the innate immune system and are rapidly recruited to the site of infection. They have several effector functions to fight invading pathogens such as the secretion of reactive oxygen species (ROS) or the release of neutrophil extracellular traps (NETs). NETs are known to promote the growth of Pasteurellaceae bacteria, especially if degraded by nucleases.

Methods

In this study, bronchoalveolar lavage fluid (BALF) from 45 field-infected pigs was analyzed for 1) NET markers, 2) influence on growth of lung bacteria, and 3) impact on neutrophil functions. BALF samples from 21 IAV-positive pigs and 24 lung diseased but IAV-negative pigs were compared.

Results

Here, we show that neutrophils in the lungs of IAV-positive pigs release vesicular NETs. Several NET markers were increased in the BALF of IAV-positive pigs compared with the BALF from IAV-negative pigs. The amount of NET markers positively correlated with the viral load of the IAV infection. Interestingly, the BALF of IAV-positive pigs enhanced the growth of bacteria belonging to the family of Pasteurellaceae as potential coinfecting bacteria. These effects were weaker with the BALF derived from IAV-negative pigs with other lung infections. The intensity of oxidative burst in neutrophils was significantly decreased by BALF from IAVpositive pigs, indicating impaired antimicrobial activity of neutrophils. Finally, the lung milieu reflected by IAV-positive BALF does not enable neutrophils to kill Actinobacillus pleuropneumoniae but rather enhances its growth.

Discussion

In summary, our data show that an IAV infection is affecting neutrophil functions, in particular the release of NETs and ROS. Furthermore, IAV infection seems to provide growth-enhancing factors for especially coinfecting Pasteurellaceae and reduces the killing efficiency of neutrophils.

Schistosome egg-derived extracellular vesicles deliver Sja-miR-71a inhibits host macrophage and neutrophil extracellular traps via targeting Sema4D

BACKGROUND

Macrophages and neutrophils are rapidly recruited around Schistosome eggs to form granulomas. Extracellular traps (ETs) of macrophages and neutrophils are part of the pathogen clearance armamentarium of leukocytes. Schistosome eggs possess the ability to resist attack by the host's immune cells and survive by employing various immune evasion mechanisms, including the release of extracellular vesicles (EVs). However, the specific mechanisms by which Schistosome egg-derived EVs (E-EVs) evade the immune response and resist attack from macrophage and neutrophil ETs remain poorly understood. In this study, we aimed to investigate the association between E-EVs and macrophage/neutrophil ETs.

METHODS

EVs were isolated from the culture supernatant of S. japonicum eggs and treated macrophages and neutrophils with E-EVs and Sja-miR-71a. The formation of ETs was then observed. Additionally, we infected mice with S. japonicum, administered HBAAV2/9-Sja-miR-71a, and the formation of macrophage ETs (METs) and neutrophil ETs (NETs) in the livers was measured. Sema4D-knockout mice, RNA sequencing, and trans-well assay were used to clarify Sja-miR-71a in E-EVs inhibits METs and NETs formation via the Sema4D/ PPAR-γ/ IL-10 axis.

RESULTS

Our findings revealed that E-EVs were internalized by macrophages and neutrophils, leading to the inhibition of METs and NETs formation. The highly expressed Sja-miR-71a in E-EVs targeted Sema4D, resulting in the up-regulation of IL-10 and subsequent inhibition of METs and NETs formation. Sema4D knockout up-regulated IL-10 expression and inhibited the formation of METs and NETs. Furthermore, we further demonstrated that Sja-miR-71a inhibits METs and NETs formation via the Sema4D/ PPAR-γ/ IL-10 axis.

CONCLUSIONS

In summary, our findings provide new insights into the immune evasion abilities of Schistosome eggs by demonstrating their ability to inhibit the formation of METs and NETs through the secretion of EVs. This study enhances our understanding of the host-pathogen interaction and may have implications for the development of novel therapeutic approaches. Video Abstract.

Acanthamoeba castellanii trophozoites escape killing by neutrophil extracellular traps using their 3'-nucleotidase/nuclease activity

Acanthamoeba castellanii is a free-living amoeba that acts as an opportunistic pathogen for humans and is the pathogenic agent of Acanthamoeba keratitis (AK). A. castellanii may present as proliferative and infective trophozoites or as resistant cysts during their life cycle. The immune response against AK is still poorly explored; however, it is well established that macrophages and neutrophils play essential roles in controlling corneal infection during the disease outcome. The release of NETs is one of the innate immune strategies to prevent parasite infection, especially when neutrophils interact with microorganisms that are too large to be phagocytosed, which is the case for amoeba species. The present work demonstrated that A. castellanii trophozoites can trigger NET formation upon in vitro interaction with neutrophils. Using DNase as a control, we observed increased parasite survival after coinciding with neutrophils, which may be correlated with NET degradation. Indeed, A. castellanii trophozoites degrade the NET DNA scaffold. Molecular analysis confirmed the occurrence of a 3'-nucleotidase/nuclease (3'-NT/NU) in the A. castellanii genome. We also demonstrated that trophozoites exhibit significantly higher 3'-NT/NU activity than cysts, which cannot trigger NET release. Considering that previous studies indicated the pathological role of 3'-NT-/NU in parasite infection, we suggest that this enzyme may act as the mechanism of escape of A. castellanii trophozoites from NETs.

Pathogenesis, epidemiology and control of Group A Streptococcus infection

Streptococcus pyogenes (Group A Streptococcus; GAS) is exquisitely adapted to the human host, resulting in asymptomatic infection, pharyngitis, pyoderma, scarlet fever or invasive diseases, with potential for triggering post-infection immune sequelae. GAS deploys a range of virulence determinants to allow colonization, dissemination within the host and transmission, disrupting both innate and adaptive immune responses to infection. Fluctuating global GAS epidemiology is characterized by the emergence of new GAS clones, often associated with the acquisition of new virulence or antimicrobial determinants that are better adapted to the infection niche or averting host immunity. The recent identification of clinical GAS isolates with reduced penicillin sensitivity and increasing macrolide resistance threatens both frontline and penicillin-adjunctive antibiotic treatment. The World Health Organization (WHO) has developed a GAS research and technology road map and has outlined preferred vaccine characteristics, stimulating renewed interest in the development of safe and effective GAS vaccines.

Neutrophil Extracellular Traps in Airway Diseases: Pathological Roles and Therapeutic Implications

Neutrophils are important effector cells of the innate immune response that fight pathogens by phagocytosis and degranulation. Neutrophil extracellular traps (NETs) are released into the extracellular space to defend against invading pathogens. Although NETs play a defensive role against pathogens, excessive NETs can contribute to the pathogenesis of airway diseases. NETs are known to be directly cytotoxic to the lung epithelium and endothelium, highly involved in acute lung injury, and implicated in disease severity and exacerbation. This review describes the role of NET formation in airway diseases, including chronic rhinosinusitis, and suggests that targeting NETs could be a therapeutic strategy for airway diseases.

Secretory proteins in the orchestration of microbial virulence: The curious case of Staphylococcus aureus

Microbial virulence showcases an excellent model for adaptive changes that enable an organism to survive and proliferate in a hostile environment and exploit host resources to its own benefit. In Staphylococcus aureus, an opportunistic pathogen of the human host, known for the diversity of the disease conditions it inflicts and the rapid evolution of antibiotic resistance, virulence is a consequence of having a highly plastic genome that is amenable to quick reprogramming and the ability to express a diverse arsenal of virulence factors. Virulence factors that are secreted to the host milieu effectively manipulate the host conditions to favor bacterial survival and growth. They assist in colonization, nutrient acquisition, immune evasion, and systemic spread. The structural and functional characteristics of the secreted virulence proteins have been shaped to assist S. aureus in thriving and disseminating effectively within the host environment and exploiting the host resources to its best benefit. With the aim of highlighting the importance of secreted virulence proteins in bacterial virulence, the present chapter provides a comprehensive account of the role of the major secreted proteins of S. aureus in orchestrating its virulence in the human host.

Bacterial DNase activity as a putative inductor of sperm DNA fragmentation in infected bull frozen-thawed semen samples

The aim of this study was to investigate the relationship between DNase activity associated with bacterial contamination of incubated bovine frozen-thawed spermatozoa and elevated sperm DNA fragmentation. Electrophoresis analysis of plasmid PBR322 incubated for 30 min at 37 °C with the supernatant of the diluent of frozen-thawed centrifuged bovine semen straws infected with bacteria showed clear evidence of DNase activity when compared to plasmid incubated in similarly prepared non-infected bovine diluent supernatant (Experiment 1). This DNase activity was subsequently found to be time dependent (0-60 min) and its activity prevented in the presence of EDTA (10 and 20 mM; Experiment 2). Semen straws infected (n = 10) and not infected (n = 10) with bacteria where incubated at 37 °C for up to 48h post-thaw. Semen infected with bacteria showed an exponential increase in bacterial growth and a corresponding increase in sperm DNA fragmentation. Non-infected semen samples showed no change in the incidence of sperm DNA fragmentation over the same period of incubation (Experiment 3). Our experiments reinforce the idea that exogenous DNases present in the semen should be considered as one of the primary contributing causes of sperm DNA fragmentation post ejaculation. In the case of the bull, post-thaw incubation of commercial straws contaminated with bacteria, resulted in increased levels of sperm DNA fragmentation, most likely associated with DNase activity (potentially restriction endonucleases) derived from the bacteria. Such adverse changes in sperm DNA fragmentation, as described here in vitro, may be also operative after insemination in the female reproductive tract (in vivo) and highlight the importance of implementing high levels of hygiene practice during semen processing, especially in light of future trends of bacterial resistance to the common antibiotics used in semen diluents.

Fate of intracellular, extracellular polymeric substances-associated, and cell-free antibiotic resistance genes in anaerobic digestion of thermally hydrolyzed sludge

Thermal hydrolysis of sludge is a promising approach to mitigate antibiotic resistance genes (ARGs) propagation in anaerobic digestion (AD). Although ARGs in sludge may be fractioned into intracellular, extracellular polymeric substance (EPS)-associated, and cell-free ARGs, the fate of these different fractions in AD has never been investigated. This study presents a detailed characterization of intracellular and extracellular ARGs in AD of sludge thermally hydrolyzed at 90 °C and 140 °C. EPS-associated ARGs represented the major fraction of the total extracellular ARGs in all samples, while its lowest abundance was observed for thermal hydrolysis at 140 °C along with the lowest EPS levels. The results suggested a positive correlation between EPS-associated ARGs with intracellular and cell-free ARGs. Furthermore, various EPS components, such as proteins and e-DNA, were positively correlated with β-lactam resistance genes. sul1 dominated all samples as an EPS-associated resistance gene. These results provide new insights into the significance of different ARGs fractions in their overall dissemination in AD integrated with thermal hydrolysis.

Interspecies competition in oral biofilms mediated by Streptococcus gordonii extracellular deoxyribonuclease SsnA

Extracellular DNA (eDNA) is a key component of many microbial biofilms including dental plaque. However, the roles of extracellular deoxyribonuclease (DNase) enzymes within biofilms are poorly understood. Streptococcus gordonii is a pioneer colonizer of dental plaque. Here, we identified and characterised SsnA, a cell wall-associated protein responsible for extracellular DNase activity of S. gordonii. The SsnA-mediated extracellular DNase activity of S. gordonii was suppressed following growth in sugars. SsnA was purified as a recombinant protein and shown to be inactive below pH 6.5. SsnA inhibited biofilm formation by Streptococcus mutans in a pH-dependent manner. Further, SsnA inhibited the growth of oral microcosm biofilms in human saliva. However, inhibition was ameliorated by the addition of sucrose. Together, these data indicate that S. gordonii SsnA plays a key role in interspecies competition within oral biofilms. Acidification of the medium through sugar catabolism could be a strategy for cariogenic species such as S. mutans to prevent SsnA-mediated exclusion from biofilms.

Neutrophil extracellular traps: Modulation mechanisms by pathogens

Neutrophils, as innate effector cells, play an essential role in the containment and elimination of pathogens. Among the main neutrophil mechanisms use for these processes is the release of neutrophil extracellular traps (NETs), which consist of decondensed DNA decorated with various cytoplasmic proteins. NETs' principal role is the trapping and elimination of infectious agents; therefore, the formation of NETs is regulated by bacteria, fungi, parasites, and viruses through different mechanisms: the presence of virulence factors (adhered or secreted), microbial load, size of the microorganism, and even due to other immune cells activation (mainly platelets). This review summarizes the significant aspects that contribute to NETs modulation by pathogens and their components, and the effect NETs have on these pathogens as a cellular defense mechanism.

Overcoming Antibiotic Resistance with Novel Paradigms of Antibiotic Selection

Conventional antimicrobial susceptibility tests, including phenotypic and genotypic methods, are insufficiently accurate and frequently fail to identify effective antibiotics. These methods predominantly select therapies based on the antibiotic response of only the lead bacterial pathogen within pure bacterial culture. However, this neglects the fact that, in the majority of human infections, the lead bacterial pathogens are present as a part of multispecies communities that modulate the response of these lead pathogens to antibiotics and that multiple pathogens can contribute to the infection simultaneously. This discrepancy is a major cause of the failure of antimicrobial susceptibility tests to detect antibiotics that are effective in vivo. This review article provides a comprehensive overview of the factors that are missed by conventional antimicrobial susceptibility tests and it explains how accounting for these methods can aid the development of novel diagnostic approaches.

Virulence factors of Streptococcus anginosus - a molecular perspective

Streptococcus anginosus together with S. constellatus and S. intermedius constitute the Streptococcus anginosus group (SAG), until recently considered to be benign commensals of the human mucosa isolated predominantly from oral cavity, but also from upper respiratory, intestinal, and urogenital tracts. For years the virulence potential of SAG was underestimated, mainly due to complications in correct species identification and their assignment to the physiological microbiota. Still, SAG representatives have been associated with purulent infections at oral and non-oral sites resulting in abscesses formation and empyema. Also, life threatening blood infections caused by SAG have been reported. However, the understanding of SAG as potential pathogen is only fragmentary, albeit certain aspects of SAG infection seem sufficiently well described to deserve a systematic overview. In this review we summarize the current state of knowledge of the S. anginosus pathogenicity factors and their mechanisms of action.

Novel prokaryotic system employing previously unknown nucleic acids-based receptors

The present study describes a previously unknown universal system that orchestrates the interaction of bacteria with the environment, named the Teazeled receptor system (TR-system). The identical system was recently discovered within eukaryotes. The system includes DNA- and RNA-based molecules named "TezRs", that form receptor's network located outside the membrane, as well as reverse transcriptases and integrases. TR-system takes part in the control of all major aspects of bacterial behavior, such as intra cellular communication, growth, biofilm formation and dispersal, utilization of nutrients including xenobiotics, virulence, chemo- and magnetoreception, response to external factors (e.g., temperature, UV, light and gas content), mutation events, phage-host interaction, and DNA recombination activity. Additionally, it supervises the function of other receptor-mediated signaling pathways. Importantly, the TR-system is responsible for the formation and maintenance of cell memory to preceding cellular events, as well the ability to "forget" preceding events. Transcriptome and biochemical analysis revealed that the loss of different TezRs instigates significant alterations in gene expression and proteins synthesis.

Taurine inhibits Streptococcus uberis-induced NADPH oxidase-dependent neutrophil extracellular traps via TAK1/MAPK signaling pathways

Neutrophil extracellular traps (NETs) are produced by neutrophil activation and usually have both anti-infective and pro-damage effects. Streptococcus uberis (S. uberis), one of the common causative organisms of mastitis, can lead to the production of NETs. Taurine, a free amino acid abundant in the organism, has been shown to have immunomodulatory effects. In this study, we investigated the molecular mechanisms of S. uberis-induced NETs formation and the regulatory role of taurine. The results showed that NETs had a disruptive effect on mammary epithelial cells and barriers, but do not significantly inhibit the proliferation of S. uberis. S. uberis induced NADPH oxidase-dependent NETs. TLR2-mediated activation of the MAPK signaling pathway was involved in this process. Taurine could inhibit the activation of MAPK signaling pathway and NADPH oxidase by modulating the activity of TAK1, thereby inhibiting the production of ROS and NETs. The effects of taurine on NADPH oxidase and NETs in S. uberis infection were also demonstrated in vivo. These results suggest that taurine can protect mammary epithelial cells and barriers from damage by reducing S. uberis-induced NETs. These data provide new insights and strategies for the prevention and control of mastitis.

Pathogen-Derived Nucleases: An Effective Weapon for Escaping Extracellular Traps

Since the 2004 publication of the first study describing extracellular traps (ETs) from human neutrophils, several reports have shown the presence of ETs in a variety of different animals and plants. ETs perform two important functions of immobilizing and killing invading microbes and are considered a novel part of the phagocytosis-independent, innate immune extracellular defense system. However, several pathogens can release nucleases that degrade the DNA backbone of ETs, reducing their effectiveness and resulting in increased pathogenicity. In this review, we examined the relevant literature and summarized the results on bacterial and fungal pathogens and parasites that produce nucleases to evade the ET-mediated host antimicrobial mechanism.

The Expanding Role of Extracellular Traps in Inflammation and Autoimmunity: The New Players in Casting Dark Webs

The first description of a new form of neutrophil cell death distinct from that of apoptosis or necrosis was discovered in 2004 and coined neutrophil extracellular traps "(NETs)" or "NETosis". Different stimuli for NET formation, and pathways that drive neutrophils to commit to NETosis have been elucidated in the years that followed. Critical enzymes required for NET formation have been discovered and targeted therapeutically. NET formation is no longer restricted to neutrophils but has been discovered in other innate cells: macrophages/monocytes, mast Cells, basophils, dendritic cells, and eosinophils. Furthermore, extracellular DNA can also be extruded from both B and T cells. It has become clear that although this mechanism is thought to enhance host defense by ensnaring bacteria within large webs of DNA to increase bactericidal killing capacity, it is also injurious to innocent bystander tissue. Proteases and enzymes released from extracellular traps (ETs), injure epithelial and endothelial cells perpetuating inflammation. In the context of autoimmunity, ETs release over 70 well-known autoantigens. ETs are associated with pathology in multiple diseases: lung diseases, vasculitis, autoimmune kidney diseases, atherosclerosis, rheumatoid arthritis, cancer, and psoriasis. Defining these pathways that drive ET release will provide insight into mechanisms of pathological insult and provide potential therapeutic targets.

Comparative Reverse Vaccinology of Piscirickettsia salmonis, Aeromonas salmonicida, Yersinia ruckeri, Vibrio anguillarum and Moritella viscosa, Frequent Pathogens of Atlantic Salmon and Lumpfish Aquaculture

Marine finfish aquaculture is affected by diverse infectious diseases, and they commonly occur as co-infection. Some of the most frequent and prevalent Gram-negative bacterial pathogens of the finfish aquaculture include Piscirickettsia salmonis, Aeromonas salmonicida, Yersinia ruckeri, Vibrio anguillarum and Moritella viscosa. To prevent co-infections in aquaculture, polyvalent or universal vaccines would be ideal. Commercial polyvalent vaccines against some of these pathogens are based on whole inactivated microbes and their efficacy is controversial. Identification of common antigens can contribute to the development of effective universal or polyvalent vaccines. In this study, we identified common and unique antigens of P. salmonis, A. salmonicida, Y. ruckeri, V. anguillarum and M. viscosa based on a reverse vaccinology pipeline. We screened the proteome of several strains using complete available genomes and identified a total of 154 potential antigens, 74 of these identified antigens corresponded to secreted proteins, and 80 corresponded to exposed outer membrane proteins (OMPs). Further analysis revealed the outer membrane antigens TonB-dependent siderophore receptor, OMP assembly factor BamA, the LPS assembly protein LptD and secreted antigens flagellar hook assembly protein FlgD and flagellar basal body rod protein FlgG are present in all pathogens used in this study. Sequence and structural alignment of these antigens showed relatively low percentage sequence identity but good structural homology. Common domains harboring several B-cells and T-cell epitopes binding to major histocompatibility (MHC) class I and II were identified. Selected peptides were evaluated for docking with Atlantic salmon (Salmo salar) and Lumpfish MHC class II. Interaction of common peptide-MHC class II showed good in-silico binding affinities and dissociation constants between −10.3 to −6.5 kcal mol−1 and 5.10 × 10−9 to 9.4 × 10−6 M. This study provided the first list of antigens that can be used for the development of polyvalent or universal vaccines against these Gram-negative bacterial pathogens affecting finfish aquaculture.

Streptococcal Pharyngitis and Rheumatic Fever

Streptococcus pyogenes (Group A Streptococcus) causes a variety of diseases, from benign self-limiting infections of the skin or throat to lethal infections of soft tissue accompanied by multi-organ failure. GAS is one of significant species among Gram-positive pathogens which is responsible for several suppurative infections and non-suppurative sequelae. They also cause pharyngitis, streptococcal toxic shock syndrome (STSS), necrotizing fasciitis and other diseases. Currently, global burden of RF / RHD is undervalued. In 2010, RF and RHD were estimated as 15.6 million cases and deaths around 200,000 annually. Laboratory diagnosis includes cultural techniques, serology, PYR test, Bacitracin susceptibility test and antibiotic resistance testing helps in differentiating the Streptococcus pyogenes from other groups of Streptococci. Most of the Acute Rheumatic Fever cases gets missed or does not present in the initial stage rather it has been developed into advanced Rheumatic Heart Disease condition. Modified Jones criteria in 2015 will be helpful especially to the low risk population as it is challenging because of limited access to primary health care, diagnosis of streptococcal disease. In addition to this revised criteria, diagnosis still relies on clinical diagnostic algorithm. Vaccines based on M protein and T antigens are continuing to evolve with different results. Ongoing vaccine development is still challenging for the GAS research community, it will make a positive and lasting impact on the peoples globally.

Immunity to Sda1 Protects against Infection by Sda1+ and Sda1- Serotypes of Group A Streptococcus

Group A Streptococcus (GAS) causes a variety of diseases globally. The DNases in GAS promote GAS evasion of neutrophil killing by degrading neutrophil extracellular traps (NETs). Sda1 is a prophage-encoded DNase associated with virulent GAS strains. However, protective immunity against Sda1 has not been determined. In this study, we explored the potential of Sda1 as a vaccine candidate. Sda1 was used as a vaccine to immunize mice intranasally. The effect of anti-Sda1 IgG in neutralizing degradation of NETs was determined and the protective role of Sda1 was investigated with intranasal and systemic challenge models. Antigen-specific antibodies were induced in the sera and pharyngeal mucosal site after Sda1 immunization. The anti-Sda1 IgG efficiently prevented degradation of NETs by supernatant samples from different GAS serotypes with or without Sda1. Sda1 immunization promoted clearance of GAS from the nasopharynx independent of GAS serotypes but did not reduce lethality after systemic GAS challenge. Anti-Sda1 antibody can neutralize degradation of NETs by Sda1 and other phage-encoded DNases and decrease GAS colonization at the nasopharynx across serotypes. These results indicate that Sda1 can be a potential vaccine candidate for reduction in GAS reservoir and GAS tonsillitis-associated diseases.

DNase I functional microgels for neutrophil extracellular trap disruption

Neutrophil extracellular traps (NETs) are web-like chromatin structures produced and liberated by neutrophils under inflammatory conditions which also promote the activation of the coagulation cascade and thrombus formation. The formation of NETs is quite prominent when blood comes in contact with artificial surfaces like extracorporeal circuits, oxygenator membranes, or intravascular grafts. DNase I as a factor of the host defense system, digests the DNA backbone of NETs, which points out its treatment potential for NET-mediated thrombosis. However, the low serum stability of DNase I restricts its clinical/therapeutic applications. To improve the bioavailability of the enzyme, DNase I was conjugated to the microgels (DNase I MG) synthesized from highly hydrophilic N-(2-hydroxypropyl) methacrylamide (HPMA) and zwitterionic carboxybetaine methacrylamide (CBMAA). The enzyme was successfully conjugated to the microgels without any alternation to its secondary structure. The K_m value representing the enzymatic activity of the conjugated DNase I was calculated to be 0.063 μM demonstrating a high enzyme-substrate affinity. The DNase I MGs were protein repellant and were able to digest NETs more efficiently compared to free DNase in a biological media, remarkably even after long-term exposure to the stimulated neutrophils continuously releasing NETs. Overall, the conjugation of DNase I to a non-fouling microgel provides a novel biohybrid platform that can be exploited as non-thrombogenic active microgel-based coatings for blood-contacting surfaces to reduce the NET-mediated inflammation and microthrombi formation.

Stage-Specific Class I Nucleases of Leishmania Play Important Roles in Parasite Infection and Survival

Protozoans of the genus Leishmania are the causative agents of an important neglected tropical disease referred to as leishmaniasis. During their lifecycle, the parasites can colonize the alimentary tract of the sand fly vector and the parasitophorous vacuole of the mammalian host, differentiating into distinct stages. Motile promastigotes are found in the sand fly vector and are transmitted to the mammalian host during the insect blood meal. Once in the vertebrate host, the parasites differentiate into amastigotes and multiply inside macrophages. To successfully establish infection in mammalian hosts, Leishmania parasites exhibit various strategies to impair the microbicidal power of the host immune system. In this context, stage-specific class I nucleases play different and important roles related to parasite growth, survival and development. Promastigotes express 3’-nucleotidase/nuclease (3’-NT/NU), an ectoenzyme that can promote parasite escape from neutrophil extracellular traps (NET)-mediated death through extracellular DNA hydrolysis and increase Leishmania-macrophage interactions due to extracellular adenosine generation. Amastigotes express secreted nuclease activity during the course of human infection that may be involved in the purine salvage pathway and can mobilize extracellular nucleic acids available far from the parasite. Another nuclease expressed in amastigotes (P4/LmC1N) is located in the endoplasmic reticulum of the parasite and may be involved in mRNA stability and DNA repair. Homologs of this class I nuclease can induce protection against infection by eliciting a T helper 1-like immune response. These immunogenic properties render these nucleases good targets for the development of vaccines against leishmaniasis, mainly because amastigotes are the form responsible for the development and progression of the disease. The present review aims to present and discuss the roles played by different class I nucleases during the Leishmania lifecycle, especially regarding the establishment of mammalian host infection.

Multi-facets of neutrophil extracellular trap in infectious diseases: Moving beyond immunity

Neutrophil extracellular traps (NETs) are networks of extracellular chromosomal DNA fibers, histones, and cytoplasmic granule proteins. The release of NET components from neutrophils is involved in the suppression of pathogen diffusion. Development of NETs around target microbes leads to disruption of the cell membrane, eventuating in kind of cell death that is called as NETosis. The very first step in the process of NETosis is activation of Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase upon signaling by innate immune receptors. Afterwards, produced Reactive oxygen species (ROS) trigger protein-arginine deiminase type 4, neutrophil elastase, and myeloperoxidase to generate decondensed chromatin and disrupted integrity of nuclear membrane. Subsequently, decondensed chromatin is mixed with several enzymes in the cytoplasm released from granules, leading to release of DNA and histones, and finally formation of NET. Several reports have indicated that NETosis might contribute to the immune responses through limiting the dissemination of microbial organisms. In this review, we discuss recent advances on the role of neutrophils, NETs, and their implications in the pathogenesis of microbial infections. Additionally, the prospective of the NET modulation as a therapeutic strategy to treat infectious diseases are clarified.

Genomic insights on DNase production in Streptococcus agalactiae ST17 and ST19 strains

Streptococcus agalactiae evasion from the human defense mechanisms has been linked to the production of DNases. These were proposed to contribute to the hypervirulence of S. agalactiae ST17/capsular-type III strains, mostly associated with neonatal meningitis. We performed a comparative genomic analysis between ST17 and ST19 human strains with different cell tropism and distinct DNase production phenotypes. All S. agalactiae ST17 strains, with the exception of 2211-04, were found to display DNase activity, while the opposite scenario was observed for ST19, where 1203-05 was the only DNase(+) strain. The analysis of the genetic variability of the seven genes putatively encoding secreted DNases in S. agalactiae revealed an exclusive amino acid change in the predicted signal peptide of GBS0661 (NucA) of the ST17 DNase(-), and an exclusive amino acid change alteration in GBS0609 of the ST19 DNase(+) strain. Further core-genome analysis identified some specificities (SNVs or indels) differentiating the DNase(-) ST17 2211-04 and the DNase(+) ST19 1203-05 from the remaining strains of each ST. The pan-genomic analysis evidenced an intact phage without homology in S. agalactiae and a transposon homologous to TnGBS2.3 in ST17 DNase(-) 2211-04; the transposon was also found in one ST17 DNase(+) strain, yet with a different site of insertion. A group of nine accessory genes were identified among all ST17 DNase(+) strains, including the Eco47II family restriction endonuclease and the C-5 cytosine-specific DNA methylase. None of these loci was found in any DNase(-) strain, which may suggest that these proteins might contribute to the lack of DNase activity. In summary, we provide novel insights on the genetic diversity between DNase(+) and DNase(-) strains, and identified genetic traits, namely specific mutations affecting predicted DNases (NucA and GBS0609) and differences in the accessory genome, that need further investigation as they may justify distinct DNase-related virulence phenotypes in S. agalactiae.

Staphylococcus aureus entanglement in self-assembling β-peptide nanofibres decorated with vancomycin

The increasing resistance of pathogenic microbes to antimicrobials and the shortage of antibiotic drug discovery programs threaten the clinical use of antibiotics. This threat calls for the development of new methods for control of drug-resistant microbial pathogens. We have designed, synthesised and characterised an antimicrobial material formed via the self-assembly of a population of two distinct β-peptide monomers, a lipidated tri-β-peptide (β3-peptide) and a novel β3-peptide conjugated to a glycopeptide antibiotic, vancomycin. The combination of these two building blocks resulted in fibrous assemblies with distinctive structures determined by atomic force microscopy and electron microscopy. These fibres inhibited the growth of methicillin resistant Staphylococcus aureus (MRSA) and associated directly with the bacteria, acting as a peptide nanonet with fibre nucleation sites on the bacteria observed by electron microscopy and confocal microscopy. Our results provide insights into the design of peptide based supramolecular assemblies with antibacterial activity and establish an innovative strategy to develop self-assembled antimicrobial materials for future biomedical application.

Searching for putative virulence factors in the genomes of Shewanella indica and Shewanella algae

Bacterial pathogens are a major threat to both humans and animals worldwide. It is crucial to understand the mechanisms of various disease processes at the molecular level. Shewanella species are widespread in the environment and some are considered as emerging opportunistic human and marine mammal pathogens. In this study, putative virulence factors on the genome of Shewanella indica BW, a bacterium isolated from the Bryde's whale (Balaenoptera edeni), were determined. Additionally, for comparative purposes, putative virulence factors from two other S. indica and ten S. algae strains were also determined using the Pathosystems Resource Integration Center (PATRIC) pipeline. We confirmed the presence of previously reported virulence factors and we are proposing several new candidate virulence factors. Interestingly, the putative virulence factors were very similar between the two species with the exception of microbial collagenase which was present in all S. algae genomes, but absent in all S. indica genomes.

Hookworms Evade Host Immunity by Secreting a Deoxyribonuclease to Degrade Neutrophil Extracellular Traps

Hookworms cause a major neglected tropical disease, occurring after larvae penetrate the host skin. Neutrophils are phagocytes that kill large pathogens by releasing neutrophil extracellular traps (NETs), but whether they target hookworms during skin infection is unknown. Using a murine hookworm, Nippostrongylus brasiliensis, we observed neutrophils being rapidly recruited and deploying NETs around skin-penetrating larvae. Neutrophils depletion or NET inhibition altered larvae behavior and enhanced the number of adult worms following murine infection. Nevertheless, larvae were able to mitigate the effect of NETs by secreting a deoxyribonuclease (Nb-DNase II) to degrade the DNA backbone. Critically, neutrophils were able to kill larvae in vitro, which was enhanced by neutralizing Nb-DNase II. Homologs of Nb-DNase II are present in other nematodes, including the human hookworm, Necator americanus, which also evaded NETs in vitro. These findings highlight the importance of neutrophils in hookworm infection and a potential conserved mechanism of immune evasion.

Complete genome sequences of Streptococcus pyogenes type strain reveal 100%-match between PacBio-solo and Illumina-Oxford Nanopore hybrid assemblies

We present the first complete, closed genome sequences of Streptococcus pyogenes strains NCTC 8198T and CCUG 4207T, the type strain of the type species of the genus Streptococcus and an important human pathogen that causes a wide range of infectious diseases. S. pyogenes NCTC 8198T and CCUG 4207T are derived from deposit of the same strain at two different culture collections. NCTC 8198T was sequenced, using a PacBio platform; the genome sequence was assembled de novo, using HGAP. CCUG 4207T was sequenced and a de novo hybrid assembly was generated, using SPAdes, combining Illumina and Oxford Nanopore sequence reads. Both strategies yielded closed genome sequences of 1,914,862 bp, identical in length and sequence identity. Combining short-read Illumina and long-read Oxford Nanopore sequence data circumvented the expected error rate of the nanopore sequencing technology, producing a genome sequence indistinguishable to the one determined with PacBio. Sequence analyses revealed five prophage regions, a CRISPR-Cas system, numerous virulence factors and no relevant antibiotic resistance genes. These two complete genome sequences of the type strain of S. pyogenes will effectively serve as valuable taxonomic and genomic references for infectious disease diagnostics, as well as references for future studies and applications within the genus Streptococcus.

Catching Common Cold Virus with a Net: Pyridostatin Forms Filaments in Tris Buffer That Trap Viruses-A Novel Antiviral Strategy?

The neutrophil extracellular trap (ET) is a eukaryotic host defense machinery that operates by capturing and concentrating pathogens in a filamentous network manufactured by neutrophils and made of DNA, histones, and many other components. Respiratory virus-induced ETs are involved in tissue damage and impairment of the alveolar-capillary barrier, but they also aid in fending off infection. We found that the small organic compound pyridostatin (PDS) forms somewhat similar fibrillary structures in Tris buffer in a concentration-dependent manner. Common cold viruses promote this process and become entrapped in the network, decreasing their infectivity by about 70% in tissue culture. We propose studying this novel mechanism of virus inhibition for its utility in preventing viral infection.

Neutrophil Extracellular Traps in Host Defense

Neutrophils are produced in the bone marrow and then patrol blood vessels from which they can be rapidly recruited to a site of infection. Neutrophils bind, engulf, and efficiently kill invading microbes via a suite of defense mechanisms. Diverse extracellular and intracellular microbes induce neutrophils to extrude neutrophil extracellular traps (NETs) through the process of NETosis. Here, we review the signaling mechanisms and cell biology underpinning the key NETosis pathways during infection and the antimicrobial functions of NETs in host defense.

Cross talk between intracellular pathogens and cell death

Infections with bacterial pathogens often results in the initiation of programmed cell death as part of the host innate immune defense, or as a bacterial virulence strategy. Induction of host cell death is controlled by an elaborate network of innate immune and cell death signaling pathways and manifests in different morphologically and functionally distinct forms of death, such as apoptosis, necroptosis, NETosis and pyroptosis. The mechanism by which host cell death restricts bacterial replication is highly cell-type and context depended, but its physiological importance is highlighted the diversity of strategies bacterial pathogens use to avoid induction of cell death or to block cell death signaling pathways. In this review, we discuss the latest insights into how bacterial pathogens elicit and manipulate cell death signaling, how different forms of cell death kill or restrict bacteria and how cell death and innate immune pathway cross talk to guard against pathogen-induced inhibition of host cell death.

Prevalence and Characterization ofStreptococcus pyogenesClinical Isolates from Different Hospitals and Clinics in Mansoura

Streptococcus pyogenesare associated with many bacterial diseases in both humans and animals and are capable of causing a multitude of human diseases.S. pyogenesisolates were identified by their bacitracin sensitivity, positivespy1258detection, and positive GAS latex agglutination. Different isolates were typed serotypically and genotypically by BOX-PCR. Different virulence factors were identified inS. pyogenesisolates. In addition, antimicrobial resistance was tested to eleven different antibiotics. Furthermore, the resistance mechanisms were determined phenotypically by the disc diffusion method. Finally, the correlation between both molecular and serotypes identified and the profile of virulence factors and clinical and geographical sources was determined for all isolates. Thirty-eightS. pyogenesisolates were collected from different clinical sources. Resistance testing indicated high resistance to mostly used antibiotics except amoxicillin/clavulanic acid, amoxicillin, and ampicillin. Serotyping results indicated five different serotypes, M1, M2, M3, M4, and M6, inS. pyogenesisolates, while six isolates were identified as untypeable. In addition, positive PCR results identified most of the tested SAgs genes in whichspeJgene was mostly identified followed byspeI, speC,andssagenes being identified in 81.6%, 63.3%, 60.5%, and 60.5%, respectively. However,speHwas the least detected. In contrast,speL, speM, andsmeZgenes could not be detected in all tested isolates. Finally, BOX-PCR molecular typing was a more effective clustering method when compared to the serotyping method in allS. pyogenes.In conclusion, the isolates in this study were highly resistant to mostly used antibiotics. M1 was the most identified serotype. No significant association was found between serotypes, BOX-PCR cluster groups, and SAgs genes profiles. However, by the application of BOX-PCR, effective molecular typing was obtained.

Streptococcus pyogenes genes that promote pharyngitis in primates

Streptococcus pyogenes (group A streptococcus; GAS) causes 600 million cases of pharyngitis annually worldwide. There is no licensed human GAS vaccine despite a century of research. Although the human oropharynx is the primary site of GAS infection, the pathogenic genes and molecular processes used to colonize, cause disease, and persist in the upper respiratory tract are poorly understood. Using dense transposon mutant libraries made with serotype M1 and M28 GAS strains and transposon-directed insertion sequencing, we performed genome-wide screens in the nonhuman primate (NHP) oropharynx. We identified many potentially novel GAS fitness genes, including a common set of 115 genes that contribute to fitness in both genetically distinct GAS strains during experimental NHP pharyngitis. Targeted deletion of 4 identified fitness genes/operons confirmed that our newly identified targets are critical for GAS virulence during experimental pharyngitis. Our screens discovered many surface-exposed or secreted proteins - substrates for vaccine research - that potentially contribute to GAS pharyngitis, including lipoprotein HitA. Pooled human immune globulin reacted with purified HitA, suggesting that humans produce antibodies against this lipoprotein. Our findings provide new information about GAS fitness in the upper respiratory tract that may assist in translational research, including developing novel vaccines.

Group A Streptococcus establishes pharynx infection by degrading the deoxyribonucleic acid of neutrophil extracellular traps

Group A Streptococcus (GAS) secretes deoxyribonucleases and evades neutrophil extracellular killing by degrading neutrophil extracellular traps (NETs). However, limited information is currently available on the interaction between GAS and NETs in the pathogenicity of GAS pharyngitis. In this study, we modified a mouse model of GAS pharyngitis and revealed an essential role for DNase in this model. After intranasal infection, the nasal mucosa was markedly damaged near the nasal cavity, at which GAS was surrounded by neutrophils. When neutrophils were depleted from mice, GAS colonization and damage to the nasal mucosa were significantly decreased. Furthermore, mice infected with deoxyribonuclease knockout GAS mutants (∆spd, ∆endA, and ∆sdaD2) survived significantly better than those infected with wild-type GAS. In addition, the supernatants of digested NETs enhanced GAS-induced cell death in vitro. Collectively, these results indicate that NET degradation products may contribute to the establishment of pharyngeal infection caused by GAS.

Machine Learning to Quantitate Neutrophil NETosis

We introduce machine learning (ML) to perform classification and quantitation of images of nuclei from human blood neutrophils. Here we assessed the use of convolutional neural networks (CNNs) using free, open source software to accurately quantitate neutrophil NETosis, a recently discovered process involved in multiple human diseases. CNNs achieved >94% in performance accuracy in differentiating NETotic from non-NETotic cells and vastly facilitated dose-response analysis and screening of the NETotic response in neutrophils from patients. Using only features learned from nuclear morphology, CNNs can distinguish between NETosis and necrosis and between distinct NETosis signaling pathways, making them a precise tool for NETosis detection. Furthermore, by using CNNs and tools to determine object dispersion, we uncovered differences in NETotic nuclei clustering between major NETosis pathways that is useful in understanding NETosis signaling events. Our study also shows that neutrophils from patients with sickle cell disease were unresponsive to one of two major NETosis pathways. Thus, we demonstrate the design, performance, and implementation of ML tools for rapid quantitative and qualitative cell analysis in basic science.

Antimicrobial resistance of pathogenic Aeromonas spp. isolated from marketed Pacific abalone (Haliotis discus hannai) in Korea

AIMS

The object of this study was to identify potential health concerns of the Aeromons spp. isolated from marketed Pacific abalone (Haliotis discus hannai) with respect to their virulence and antimicrobial resistance patterns.

METHODS AND RESULTS

We identified 29 strains of aeromonads consisting of five species; Aeromonas hydrophila (n = 9), Aeromonas enteropelogenes (n = 14), Aeromonas veronii (n = 3), Aeromonas salmonicida (n = 2) and Aeromonas sobria (n = 1), by employing series of biochemical tests and gene sequencing. In the phenotypic virulence assays, all isolates showed gelatinase and caseinase activities, while lipase formation (69%), phospholipase production (90%), DNase formation (82%), slime production (49%) and haemolysis activity (α = 18% and β = 82%) were also detected among isolates. Prevalence of virulence genes; aerA (100%), fla (66%), ahyB (73%), act (52%), alt (42%), ast (35%), ser (52%), gcat (69%), ascV (43%), hlyA (83%), lip (52%) and exu (59%) were detected by PCR assays. In disc diffusion test, 100% resistance was detected against ampicillin while cephalothin, rifampicin, oxytetracycline, colistine sulphate, nalidixic acid and piperaciliin were resisted by 86, 73, 42, 35, 28, 20 and 20% of the isolates respectively. Thirteen (45%) of the isolates showed multiple antimicrobial resistance (MAR) indices ≥ 0·2.

CONCLUSIONS

Our findings suggest that the potential health risk posed by the abalone-borne Aeromonas spp. should not be underestimated.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time to evaluate possible public health risks upon consumption of abalone harbored Aeromonas spp. and also to isolate potential pathogenic and multidrug-resistant Aeromonas spp. from Pacific abalone in Korea.

Degraded neutrophil extracellular traps promote the growth of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae (A.pp) causes severe pneumonia associated with enormous economic loss in pigs. Peracute diseased pigs die in <24 h with pneumonia. Neutrophils are the prominent innate immune cell in this infection that massively infiltrate the infected lung. Here we show that neutrophils release neutrophil extracellular traps (NETs) as response to A.pp infection. Numerous NET-markers were identified in bronchoalveolar lavage fluid (BALF) of A.pp-infected piglets in vivo, however, most NET fibers are degraded. Importantly, A.pp is able to enhance its growth rate in the presence of NETs that have been degraded by nucleases efficiently. A.pp itself releases no nuclease, but we identified host nucleases as sources that degrade NETs after A.pp infection. Furthermore, the nucleases of co-infecting pathogens like Streptococcus suis increase growth of A.pp in presence of porcine NETs. Thus, A.pp is not only evading the antimicrobial activity of NETs, A.pp is rather additionally using parts of NETs as growth factor thereby taking advantage of host nucleases as DNase1 or nucleases of co-infecting bacteria, which degrade NETs. This effect can be diminished by inhibiting the bacterial adenosine synthase indicating that degraded NETs serve as a source for NAD, which is required by A.pp for its growth. A similar phenotype was found for the human pathogen Haemophilus (H.) influenzae and its growth in the presence of human neutrophils. H. influenzae benefits from host nucleases in the presence of neutrophils. These data shed light on the detrimental effects of NETs during host immune response against certain bacterial species that require and/or efficiently take advantage of degraded DNA material, which has been provided by host nuclease or nucleases of other co-infecting bacteria, as growth source.

Off-on switching of enzyme activity by near-infrared light-induced photothermal phase transition of nanohybrids

The off-on manipulation of enzyme activity is a challenging task. We report a new strategy for reversible off-on control of enzyme activity by near-infrared light. Enzymes acting on macromolecular substrates are embedded with an ultrasmall platinum nanoparticle and decorated with thermoresponsive copolymers, which exhibit upper critical solution temperature (UCST) behavior. The polymer-enzyme nanohybrids form microscale aggregates in solution below the UCST to prevent macromolecular substrates from approaching the enzymes and thus inhibit the enzyme activity, and they disassemble above the UCST to reactivate the enzyme. Upon near-infrared irradiation, platinum nanoparticles inside the enzymes generate heat through a photothermal effect to cause phase transition of the copolymers. Therefore, we can reversibly switch off and on the activities of three enzymes acting on polysaccharide, protein, and plasmid. The enzyme activities are increased by up to 61-fold after laser irradiation. This study provides a facile and efficient method for off-on control of enzyme activity.

The Emerging Role of Neutrophil Extracellular Traps in Respiratory Disease

Neutrophil extracellular traps (NETs) are extrusions of intracellular DNA and attached granular material that enable bacterial killing. NETs are increasingly recognized for their role in the pathogenesis of respiratory disease. NETs are composed of a complex mix of intracellularly derived material that neutrophils organize within the cytoplasm and then expel in a nondirected manner in the vicinity of invading organisms. Combined, these trap and destroy multiple genera of microbes including bacteria, fungi, viruses, and protozoans, limiting infection especially where phagocytosis is not possible. At first, NET formation was thought to be a terminal event for neutrophils; however, it is now apparent that some neutrophils survive this process, becoming anuclear, and may drive ongoing tissue damage. NETs are now known to be directly cytotoxic to lung epithelium and endothelium, and their excessive production is seen in pneumonia and acute lung injury as well as several chronic diseases, including COPD, asthma, and cystic fibrosis. NETs also appear to play a role in both tumor defense and dissemination, depending on the local microenvironment and the specific tumor subtype. It is becoming increasingly apparent that NET formation can exert a positive or negative influence on multiple respiratory pathologies and that simply globally reducing or increasing NET formation is unlikely to be a therapeutic success. Rather, as our understanding grows, it is likely that targeted NET up- or downregulation along with destruction or protection of already formed NETs may become an additional point of intervention for respiratory physicians.

A DNase from a Fungal Phytopathogen Is a Virulence Factor Likely Deployed as Counter Defense against Host-Secreted Extracellular DNA

We document that the absence of a single gene encoding a DNase in a fungal plant pathogen results in significantly reduced virulence to a plant host. We compared a wild-type strain of the maize pathogen Cochliobolus heterostrophus and an isogenic mutant lacking a candidate secreted DNase-encoding gene and demonstrated that the mutant is reduced in virulence on leaves and on roots. There are no previous reports of deletion of such a gene from either an animal or plant fungal pathogen accompanied by comparative assays of mutants and wild type for alterations in virulence. We observed DNase activity, in fungal culture filtrates, that is Mg²⁺ dependent and induced when plant host leaf material is present. Our findings demonstrate not only that fungi use extracellular DNases (exDNases) for virulence, but also that the relevant molecules are deployed in above-ground leaves as well as below-ground plant tissues. Overall, these data provide support for a common defense/counter defense virulence mechanism used by animals, plants, and their fungal and bacterial pathogens and suggest that components of the mechanism might be novel targets for the control of plant disease.

Histone-linked extracellular DNA (exDNA) is a component of neutrophil extracellular traps (NETs). NETs have been shown to play a role in immune response to bacteria, fungi, viruses, and protozoan parasites. Mutation of genes encoding group A Streptococcus extracellular DNases (exDNases) results in reduced virulence in animals, a finding that implies that exDNases are deployed as counter defense against host DNA-containing NETs. Is the exDNA/exDNase mechanism also relevant to plants and their pathogens? It has been demonstrated previously that exDNA is a component of a matrix secreted from plant root caps and that plants also carry out an extracellular trapping process. Treatment with DNase I destroys root tip resistance to infection by fungi, the most abundant plant pathogens. We show that the absence of a single gene encoding a candidate exDNase results in significantly reduced virulence of a fungal plant pathogen to its host on leaves, the known infection site, and on roots. Mg²⁺-dependent exDNase activity was demonstrated in fungal culture filtrates and induced when host leaf material was present. It is speculated that the enzyme functions to degrade plant-secreted DNA, a component of a complex matrix akin to neutrophil extracellular traps of animals.