Neuraminidase expressed by Streptococcus pneumoniae desialylates the lipopolysaccharide of Neisseria meningitidis and Haemophilus influenzae: a paradigm for interbacterial competition among pathogens of the human respiratory tract

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Effects of Contagious Respiratory Pathogens on Breath Biomarkers

Due to their immediate exhalation after generation at the cellular/microbiome levels, exhaled volatile organic compounds (VOCs) may provide real-time information on pathophysiological mechanisms and the host response to infection. In recent years, the metabolic profiling of the most frequent respiratory infections has gained interest as it holds potential for the early, non-invasive detection of pathogens and the monitoring of disease progression and the response to therapy. Using previously unpublished data, randomly selected individuals from a COVID-19 test center were included in the study. Based on multiplex PCR results (non-SARS-CoV-2 respiratory pathogens), the breath profiles of 479 subjects with the presence or absence of flu-like symptoms were obtained using proton-transfer-reaction time-of-flight mass spectrometry. Among 223 individuals, one respiratory pathogen was detected in 171 cases, and more than one pathogen in 52 cases. A total of 256 subjects had negative PCR test results and had no symptoms. The exhaled VOC profiles were affected by the presence of Haemophilus influenzae, Streptococcus pneumoniae, and Rhinovirus. The endogenous ketone, short-chain fatty acid, organosulfur, aldehyde, and terpene concentrations changed, but only a few compounds exhibited concentration changes above inter-individual physiological variations. Based on the VOC origins, the observed concentration changes may be attributed to oxidative stress and antioxidative defense, energy metabolism, systemic microbial immune homeostasis, and inflammation. In contrast to previous studies with pre-selected patient groups, the results of this study demonstrate the broad inter-individual variations in VOC profiles in real-life screening conditions. As no unique infection markers exist, only concentration changes clearly above the mentioned variations can be regarded as indicative of infection or colonization.

Exploring the biomedical potential of a novel modified glass ionomer cement against the pandrug-resistant oral pathogen Candida albicans SYN-01

Dental caries is an infectious disease that is a major concern for dentists. Streptococci and Lactobacilli were long thought to be the primary etiology responsible for caries. Candida albicans with acidogenic and aciduric characteristics has recently been implicated in the onset and progression of cariogenic lesions. Moreover, due to the increased resistance to common antimicrobials, the discovery of innovative candidates is in high demand. Therefore, our study might be the first report that explores the efficacy of glass ionomer cement (GIC) incorporated with a newly modified carboxylated chitosan derivative (CS-MC) against multidrug-resistant (MDR) and/or pandrug resistant (PDR) C. albicans isolated from the oral cavity. In this work, four CS-MC-GIC groups with different concentrations were formulated. Group four (CS-MC-GIC-4) gave a significant performance as an anticandidal agent against selected PDR Candida strain, with an obvious decrease in its cell viability and high antibiofilm activity. It also, enhanced all the mechanical properties and supports cell viability of Vero cells as a nontoxic compound. Moreover, CS-MC-GIC-4 inhibited neuraminidases completely, which might provide a novel mechanism to prevent dental/oral infections. Thus, findings in this study open up new prospect of the utilization of CS-MC-GIC as a novel dental filling material against oral drug-resistant Candida.

Solving polymicrobial puzzles: evolutionary dynamics and future directions

Polymicrobial infections include various microorganisms, often necessitating different treatment methods than a monomicrobial infection. Scientists have been puzzled by the complex interactions within these communities for generations. The presence of specific microorganisms warrants a chronic infection and impacts crucial factors such as virulence and antibiotic susceptibility. Game theory is valuable for scenarios involving multiple decision-makers, but its relevance to polymicrobial infections is limited. Eco-evolutionary dynamics introduce causation for multiple proteomic interactions like metabolic syntropy and niche segregation. The review culminates both these giants to form evolutionary dynamics (ED). There is a significant amount of literature on inter-bacterial interactions that remain unsynchronised. Such raw data can only be moulded by analysing the ED involved. The review culminates the inter-bacterial interactions in multiple clinically relevant polymicrobial infections like chronic wounds, CAUTI, otitis media and dental carries. The data is further moulded with ED to analyse the niche colonisation of two notoriously competitive bacteria: S.aureus and P.aeruginosa. The review attempts to develop a future trajectory for polymicrobial research by following recent innovative strategies incorporating ED to curb polymicrobial infections.

Respiratory Viruses and Cystic Fibrosis

The threat of respiratory virus infection to human health and well-being has been clearly highlighted by the coronavirus disease 2019 (COVID-19) pandemic. For people with cystic fibrosis (CF), the clinical significance of viral infections long predated the emergence of severe acute respiratory syndrome coronavirus 2. This article reviews the epidemiology, diagnosis, and treatment of respiratory virus infection in the context of CF as well as the current understanding of interactions between viruses and other microorganisms in the CF lung. The incidence of respiratory virus infection in CF varies by age with young children typically experiencing more frequent episodes than adolescents and adults. At all ages, respiratory viruses are very common in CF and are associated with pulmonary exacerbations. Respiratory viruses are identified at up to 69% of exacerbations, while viruses are also frequently detected during clinical stability. The full impact of COVID-19 in CF is yet to be established. Early studies found that rates of COVID-19 were lower in CF cohorts than in the general population. The reasons for this are unclear but may be related to the effects of shielding, infection control practices, maintenance CF therapies, or the inflammatory milieu in the CF lung. Observational studies have consistently identified that prior solid organ transplantation is a key risk factor for poor outcomes from COVID-19 in CF. Several key priorities for future research are highlighted. First, the impact of highly effective CFTR modulator therapy on the epidemiology and pathophysiology of viral infections in CF requires investigation. Second, the impact of respiratory viruses on the development and dynamics of the CF lung microbiota is poorly understood and viral infection may have important interactions with bacteria and fungi in the airway. Finally, bacteriophages represent a key focus of future investigation both for their role in transmission of antimicrobial resistance and as a promising treatment modality for multiresistant pathogens.

Nutritional Interactions between Bacterial Species Colonising the Human Nasal Cavity: Current Knowledge and Future Prospects

The human nasal microbiome can be a reservoir for several pathogens, including Staphylococcus aureus. However, certain harmless nasal commensals can interfere with pathogen colonisation, an ability that could be exploited to prevent infection. Although attractive as a prophylactic strategy, manipulation of nasal microbiomes to prevent pathogen colonisation requires a better understanding of the molecular mechanisms of interaction that occur between nasal commensals as well as between commensals and pathogens. Our knowledge concerning the mechanisms of pathogen exclusion and how stable community structures are established is patchy and incomplete. Nutrients are scarce in nasal cavities, which makes competitive or mutualistic traits in nutrient acquisition very likely. In this review, we focus on nutritional interactions that have been shown to or might occur between nasal microbiome members. We summarise concepts of nutrient release from complex host molecules and host cells as well as of intracommunity exchange of energy-rich fermentation products and siderophores. Finally, we discuss the potential of genome-based metabolic models to predict complex nutritional interactions between members of the nasal microbiome.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.

Sugar Coating: Utilisation of Host Serum Sialoglycoproteins by Schistosoma mansoni as a Potential Immune Evasion Mechanism

Parasitic helminths resort to various mechanisms to evade and modulate their host’s immune response, several of which have been described for Schistosoma mansoni. We recently reported the presence of sialic acid residues on the surface of adult S. mansoni extracellular vesicles (EVs). We now report that these sialylated molecules are mammalian serum proteins. In addition, our data suggest that most sialylated EV-associated proteins do not elicit a humoral response upon injection into mice, or in sera obtained from infected animals. Sialic acids frequently terminate glycans on the surface of vertebrate cells, where they serve important functions in physiological processes such as cell adhesion and signalling. Interestingly, several pathogens have evolved ways to mimic or utilise host sialic acid beneficially by coating their own proteins, thereby facilitating cell invasion and providing protection from host immune effectors. Together, our results indicate that S. mansoni EVs are coated with host glycoproteins, which may contribute to immune evasion by masking antigenic sites, protecting EVs from removal from serum and aiding in cell adhesion and entry to exert their functions.

Staphylococcus epidermidis Controls Opportunistic Pathogens in the Nose, Could It Help to Regulate SARS-CoV-2 (COVID-19) Infection?

Staphylococcus epidermidis is more abundant in the anterior nares than internal parts of the nose, but its relative abundance changes along with age; it is more abundant in adolescents than in children and adults. Various studies have shown that S. epidermidis is the guardian of the nasal cavity because it prevents the colonization and infection of respiratory pathogens (bacteria and viruses) through the secretion of antimicrobial molecules and inhibitors of biofilm formation, occupying the space of the membrane mucosa and through the stimulation of the host's innate and adaptive immunity. There is a strong relationship between the low number of S. epidermidis in the nasal cavity and the increased risk of serious respiratory infections. The direct application of S. epidermidis into the nasal cavity could be an effective therapeutic strategy to prevent respiratory infections and to restore nasal cavity homeostasis. This review shows the mechanisms that S. epidermidis uses to eliminate respiratory pathogens from the nasal cavity, also S. epidermidis is proposed to be used as a probiotic to prevent the development of COVID-19 because S. epidermidis induces the production of interferon type I and III and decreases the expression of the entry receptors of SARS-CoV-2 (ACE2 and TMPRSS2) in the nasal epithelial cells.

Innate Immunity in the Middle Ear Mucosa

Otitis media (OM) encompasses a spectrum of clinical presentations ranging from the readily identifiable Acute OM (AOM), which is characterised by otalgia and fever, to chronic otitis media with effusion (COME) where impaired hearing due to middle ear effusion may be the only clinical symptom. Chronic suppurative OM (CSOM) presents as a more severe form of OM, involving perforation of the tympanic membrane. The pathogenesis of OM in these varied clinical presentations is unclear but activation of the innate inflammatory responses to viral and/or bacterial infection of the upper respiratory tract performs an integral role. This localised inflammatory response can persist even after pathogens are cleared from the middle ear, eustachian tubes and, in the case of respiratory viruses, even the nasal compartment. Children prone to OM may experience an over exuberant inflammatory response that underlies the development of chronic forms of OM and their sequelae, including hearing impairment. Treatments for chronic effusive forms of OM are limited, with current therapeutic guidelines recommending a "watch and wait" strategy rather than active treatment with antibiotics, corticosteroids or other anti-inflammatory drugs. Overall, there is a clear need for more targeted and effective treatments that either prevent or reduce the hyper-inflammatory response associated with chronic forms of OM. Improved treatment options rely upon an in-depth understanding of OM pathogenesis, particularly the role of the host innate immune response during acute OM. In this paper, we review the current literature regarding the innate immune response within the middle ear to bacterial and viral otopathogens alone, and as co-infections. This is an important consideration, as the role of respiratory viruses as primary pathogens in OM is not yet fully understood. Furthermore, increased reporting from PCR-based diagnostics, indicates that viral/bacterial co-infections in the middle ear are more common than bacterial infections alone. Increasingly, the mechanisms by which viral/bacterial co-infections may drive or maintain complex innate immune responses and inflammation during OM as a chronic response require investigation. Improved understanding of the pathogenesis of chronic OM, including host innate immune response within the middle ear is vital for development of improved diagnostic and treatment options for our children.

Neuraminidase B controls neuraminidase A-dependent mucus production and evasion

Binding of Streptococcus pneumoniae (Spn) to nasal mucus leads to entrapment and clearance via mucociliary activity during colonization. To identify Spn factors allowing for evasion of mucus binding, we used a solid-phase adherence assay with immobilized mucus of human and murine origin. Spn bound large mucus particles through interactions with carbohydrate moieties. Mutants lacking neuraminidase A (nanA) or neuraminidase B (nanB) showed increased mucus binding that correlated with diminished removal of terminal sialic acid residues on bound mucus. The non-additive activity of the two enzymes raised the question why Spn expresses two neuraminidases and suggested they function in the same pathway. Transcriptional analysis demonstrated expression of nanA depends on the enzymatic function of NanB. As transcription of nanA is increased in the presence of sialic acid, our findings suggest that sialic acid liberated from host glycoconjugates by the secreted enzyme NanB induces the expression of the cell-associated enzyme NanA. The absence of detectable mucus desialylation in the nanA mutant, in which NanB is still expressed, suggests that NanA is responsible for the bulk of the modification of host glycoconjugates. Thus, our studies describe a functional role for NanB in sialic acid sensing in the host. The contribution of the neuraminidases in vivo was then assessed in a murine model of colonization. Although mucus-binding mutants showed an early advantage, this was only observed in a competitive infection, suggesting a complex role of neuraminidases. Histologic examination of the upper respiratory tract demonstrated that Spn stimulates mucus production in a neuraminidase-dependent manner. Thus, an increase production of mucus containing secretions appears to be balanced, in vivo, by decreased mucus binding. We postulate that through the combined activity of its neuraminidases, Spn evades mucus binding and mucociliary clearance, which is needed to counter neuraminidase-mediated stimulation of mucus secretions.

Friend or Foe: Interbacterial Competition in the Nasal Cavity

Like other microbes that live on or in the human body, the bacteria that inhabit the upper respiratory tract, in particular the nasal cavity, have evolved to survive in an environment that presents a number of physical and chemical challenges; these microbes are constantly bombarded with nutritional fluctuations, changes in humidity, the presence of inhaled particulate matter (odorants and allergens), and competition with other microbes. Indeed, only a specialized set of species is able to colonize this niche and successfully contend with the host's immune system and the constant threat from competitors. To this end, bacteria that live in the nasal cavity have evolved a variety of approaches to outcompete contenders for the limited nutrients and space; broadly speaking, these strategies may be considered a type of "bacterial warfare." A greater molecular understanding of bacterial warfare has the potential to reveal new approaches or molecules that can be developed as novel therapeutics. As such, there are many studies within the last decade that have sought to understand the complex polymicrobial interactions that occur in various environments. Here, we review what is currently known about the age-dependent structure and interbacterial relationships within the nasal microbiota and summarize the molecular mechanisms that are predicted to dictate bacterial warfare in this niche. Although the currently described interactions are complex, in reality, we have likely only scratched the surface in terms of a true understanding of the types of interbacterial competition and cooperation that are thought to take place in and on the human body.

Neisseria species and their complicated relationships with human health

Neisseria spp. are a transient low abundance member of the human microbiome. This species contains the very well described pathogens, Neisseria gonorrhoeae and N. meningitidis. Recent advances in molecular typing have revealed that this genus is more diverse than previously thought and that commensal species may have important roles in inhibiting the growth the pathogens. This short review summates these new findings and examines the evidence that the relatively under-reported Neisseria commensal species maybe beneficial to human health.

The Effect of Influenza Virus on the Human Oropharyngeal Microbiome

Background

Secondary bacterial infections are an important cause of morbidity and mortality associated with influenza infections. As bacterial disease can be caused by a disturbance of the host microbiome, we examined the impact of influenza on the upper respiratory tract microbiome in a human challenge study.

Methods

The dynamics and ecology of the throat microbiome were examined following an experimental influenza challenge of 52 previously-healthy adult volunteers with influenza A/Wisconsin/67/2005 (H3N2) by intranasal inoculation; 35 healthy control subjects were not subjected to the viral challenge. Serial oropharyngeal samples were taken over a 30-day period, and the V1-V3 region of the bacterial 16S ribosomal RNA sequences were amplified and sequenced to determine the composition of the microbiome. The carriage of pathogens was also detected.

Results

Of the 52 challenged individuals, 43 developed proven influenza infections, 33 of whom became symptomatic. None of the controls developed influenza, although 22% reported symptoms. The diversity of bacterial communities remained remarkably stable following the acquisition of influenza, with no significant differences over time between individuals with influenza and those in the control group. Influenza infection was not associated with perturbation of the microbiome at the level of phylum or genus. There was no change in colonization rates with Streptococcus pneumoniae or Neisseria meningitidis.

Conclusions

The throat microbiota is resilient to influenza infection, indicating the robustness of the upper-airway microbiome.

Viral-bacterial (co-)occurrence in the upper airways and the risk of childhood pneumonia in resource-limited settings

OBJECTIVE

To examine the association between bacterial-viral co-occurrence in the nasopharynx and the risk of community acquired pneumonia (CAP) in young children living in resource-limited settings.

METHODS

A case-control study was conducted between January and December 2017 in Moshi, Tanzania. Children 2-59 months with CAP and healthy controls were enrolled. RSV and Influenza A/B were detected with a standardized polymerase chain reaction (PCR) method, and a simplified real-time quantitative PCR method, without sample pre-processing, was developed to detect bacterial pathogens in nasopharyngeal samples.

RESULTS

A total of 109 CAP patients and 324 healthy controls were enrolled. Co-detection of H. influenzae and S. pneumoniae in nasopharyngeal swabs was linked with higher odds of CAP (aOR=3.2, 95% CI=1.1-9.5). The majority of the H. influenzae isolated in cases and controls (95.8%) were non-typeable. Of the viruses examined, respiratory syncytial virus (RSV) was most common (n = 31, 7.2%) in cases and controls. Children with RSV had 8.4 times higher odds to develop pneumonia than healthy children (aOR=8.4, 95%CI= 3.2 - 22.1).

CONCLUSIONS

Co-occurence of H. influenzae and S. pneumoniae in the nasopharynx was strongly associated with CAP. The high prevalence of non-typeable H. influenzae might be a sign of replacement as a consequence of Haemophilus influenzae type b vaccination.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Pneumococcal vaccine impacts on the population genomics of non-typeable Haemophilus influenzae

The implementation of pneumococcal conjugate vaccines (PCVs) has led to a decline in vaccine-type disease. However, there is evidence that the epidemiology of non-typeable Haemophilus influenzae (NTHi) carriage and disease can be altered as a consequence of PCV introduction. We explored the epidemiological shifts in NTHi carriage using whole genome sequencing over a 5-year period that included PCV13 replacement of PCV7 in the UK’s National Immunization Programme in 2010. Between 2008/09 and 2012/13 (October to March), nasopharyngeal swabs were taken from children <5 years of age. Significantly increased carriage post-PCV13 was observed and lineage-specific associations with Streptococcus pneumoniae were seen before but not after PCV13 introduction. NTHi were characterized into 11 discrete, temporally stable lineages, congruent with current knowledge regarding the clonality of NTHi. The increased carriage could not be linked to the expansion of a particular clone and different co-carriage dynamics were seen before PCV13 implementation when NTHi co-carried with vaccine serotype pneumococci. In summary, PCV13 introduction has been shown to have an indirect effect on NTHi epidemiology and there exists both negative and positive, distinct associations between pneumococci and NTHi. This should be considered when evaluating the impacts of pneumococcal vaccine design and policy.

Neuraminidase A from Streptococcus pneumoniae has a modular organization of catalytic and lectin domains separated by a flexible linker

Neuraminidase A (NanA) of the pathogen Streptococcus pneumoniae cleaves receptors of the human respiratory epithelial surface during bacterial colonization. The full-size structure of NanA that contains one lectin and one catalytic domain within a single polypeptide chain remains unresolved. Both domains are crucial for the microorganism's virulence and considered as promising antimicrobial targets. Methods of bioinformatics and molecular dynamics have been implemented to model NanA's structure and study interaction between the lectin and catalytic domains in three neuraminidases NanA, NanB, and NanC from Streptococcus pneumoniae. A significant difference in spatial organization of these homologous enzymes has been revealed. The lectin and catalytic domains of NanB and NanC form rigid globules stabilized by multiple interdomain interactions, whereas in NanA, the two domains are separated by a 16 amino acids long flexible linker - a characteristic of proteins that require conformational flexibility for their functioning. The biological role of this structural adaptation of NanA as a key virulence enzyme is discussed.

Glycophorin-C sialylation regulates Lu/BCAM adhesive capacity during erythrocyte aging

Lutheran/basal cell adhesion molecule (Lu/BCAM) is a transmembrane adhesion molecule expressed by erythrocytes and endothelial cells that can interact with the extracellular matrix protein laminin-α5. In sickle cell disease, Lu/BCAM is thought to contribute to adhesion of sickle erythrocytes to the vascular wall, especially during vaso-occlusive crises. On healthy erythrocytes however, its function is unclear. Here we report that Lu/BCAM is activated during erythrocyte aging. We show that Lu/BCAM-mediated binding to laminin-α5 is restricted by interacting, in cis, with glycophorin-C-derived sialic acid residues. Following loss of sialic acid during erythrocyte aging, Lu/BCAM is released from glycophorin-C and allowed to interact with sialic acid residues on laminin-α5. Decreased glycophorin-C sialylation, as observed in individuals lacking exon 3 of glycophorin-C, the so-called Gerbich phenotype, was found to correlate with increased Lu/BCAM-dependent binding to laminin-α5. In addition, we identified the sialic acid-binding site within the third immunoglobulin-like domain within Lu/BCAM that accounts for the interaction with glycophorin-C and laminin-α5. Last, we present evidence that neuraminidase-expressing pathogens, such as Streptococcus pneumoniae, can similarly induce Lu/BCAM-mediated binding to laminin-α5, by cleaving terminal sialic acid residues from the erythrocyte membrane. These results shed new light on the mechanisms contributing to increased adhesiveness of erythrocytes at the end of their lifespan, possibly facilitating their clearance. Furthermore, this work may contribute to understanding the pathology induced by neuraminidase-positive bacteria, because they are especially harmful to patients suffering from sickle cell disease and are associated with the occurrence of vaso-occlusive crises.

The nasopharyngeal microbiome

Human microbiomes have received increasing attention over the last 10 years, leading to a pervasiveness of hypotheses relating dysbiosis to health and disease. The respiratory tract has received much less attention in this respect than that of, for example, the human gut. Nevertheless, progress has been made in elucidating the immunological, ecological and environmental drivers that govern these microbial consortia and the potential consequences of aberrant microbiomes. In this review, we consider the microbiome of the nasopharynx, a specific niche of the upper respiratory tract. The nasopharynx is an important site, anatomically with respect to its gateway position between upper and lower airways, and for pathogenic bacterial colonisation. The dynamics of the latter are important for long-term respiratory morbidity, acute infections of both invasive and non-invasive disease and associations with chronic airway disease exacerbations. Here, we review the development of the nasopharyngeal (NP) microbiome over the life course, examining it from the early establishment of resilient profiles in neonates through to perturbations associated with pneumonia risk in the elderly. We focus specifically on the commensal, opportunistically pathogenic members of the NP microbiome that includes Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae and Moraxella catarrhalis. In addition, we consider the role of relatively harmless genera such as Dolosigranulum and Corynebacterium. Understanding that the NP microbiome plays such a key, beneficial role in maintaining equilibrium of commensal species, prevention of pathogen outgrowth and host immunity enables future research to be directed appropriately.

Pneumococcal neuraminidase activates TGF-β signalling

Neuraminidase A (NanA) is an important virulence factor that is anchored to the pneumococcal cell wall and cleaves sialic acid on host substrates. We noted that a secreted allele of NanA was over-represented in invasive pneumococcal isolates and promoted the development of meningitis when swapped into the genome of non-meningitis isolates replacing cell wall-anchored NanA. Both forms of recombinant NanA directly activated transforming growth factor (TGF)-β, increased SMAD signalling and promoted loss of endothelial tight junction ZO-1. However, in assays using whole bacteria, only the cell-bound NanA decreased expression of ZO-1 and showed NanA dependence of bacterial invasion of endothelial cells. We conclude that NanA secretion versus retention on the cell surface does not influence neurotropism of clinical isolates. However, we describe a new NanA-TGF-β signalling axis that leads to decreased blood-brain barrier integrity and enhances bacterial invasion.

Innate immune recognition and inflammation in Neisseria meningitidis infection

Neisseria meningitidis (Nme) can cause meningitis and sepsis, diseases which are characterised by an overwhelming inflammatory response. Inflammation is triggered by host pattern recognition receptors (PRRs) which are activated by pathogen-associated molecular patterns (PAMPs). Nme contains multiple PAMPs including lipooligosaccharide, peptidoglycan, proteins and metabolites. Various classes of PRRs including Toll-like receptors, NOD-like receptors, C-type lectins, scavenger receptors, pentraxins and others are expressed by the host to respond to any given microbe. While Toll-like receptors and NOD-like receptors are pivotal in triggering inflammation, other PRRs act as modulators of inflammation or aid in functional antimicrobial responses such as phagocytosis or complement activation. This review aims to give an overview of the various Nme PAMPs reported to date, the PRRs they activate and their implications during the inflammatory response to infection.

Role of Streptococcus pneumoniae Proteins in Evasion of Complement-Mediated Immunity

The complement system plays a central role in immune defense against Streptococcus pneumoniae. In order to evade complement attack, pneumococci have evolved a number of mechanisms that limit complement mediated opsonization and subsequent phagocytosis. This review focuses on the strategies employed by pneumococci to circumvent complement mediated immunity, both in vitro and in vivo. At last, since many of the proteins involved in interactions with complement components are vaccine candidates in different stages of validation, we explore the use of these antigens alone or in combination, as potential vaccine approaches that aim at elimination or drastic reduction in the ability of this bacterium to evade complement.

Composition and immunological significance of the upper respiratory tract microbiota

The intestinal microbiota is essential for nutrient acquisition, immune development, and exclusion of invading pathogens. The upper respiratory tract (URT) microbiota is less well studied and does not appear to abide by many of the paradigms of the gastrointestinal tract. Decades of carriage studies in children have demonstrated that microbe–microbe competition and collusion occurs in the URT. Whether colonization with common pathogens (e.g., Staphylococcus aureus and Streptococcus pneumoniae) alters immune development or susceptibility to respiratory conditions is just beginning to be understood. Herein, we discuss the biogeography of the URT microbiota, the succession and evolution of the microbiota through the life course, and discuss the evidence for microbe–microbe interactions in colonization and infection.

Detection and comparison of neuraminidase activities in human and bovine group B streptococci

Human and bovine group B streptococcus (GBS) isolates were serotyped and amounts of released N-acetylneuraminic acid from N-acetylneuraminyl-lactose by extracellular neuraminidase were colorimetrically assessed. According to serotyping by co-agglutination method, 30 of bovine GBS and 43 of human GBS could be serotyped (ST) by monospecific antisera coated with protein A. The remaining GBS strains were designated as nontypeable (NT). The released N-acetylneuraminic acid was determined in 90.9% of bovine GBS and 47.1% of human GBS isolates. The differences between the total bovine and human GBS isolates were statistically significant (p < 0.001). In comparison with detected N-acetylneuraminic acid level in bovine and human groups, significant decrease was observed in the bovine NT group according to increased human NT (p < 0.01) and bovine ST groups (p < 0.01). However, N-acetylneuraminic acid level in bovine ST and bovine total groups significantly (p < 0.001) increased with respect to the human ST group and human total group. Neuraminidase activity was detected more frequently in bovine GBS isolates. Considerable differentiations were observed between typeable and nontypeable isolates.

Impact of micro-environmental changes on respiratory tract infections with intracellular bacteria

Community-acquired pneumonia is caused by intra- and extracellular bacteria, with some of these bacteria also being linked to the pathogenesis of chronic lung diseases, including asthma and chronic obstructive pulmonary disease. Chlamydia pneumoniae is an obligate intracellular pathogen that is highly sensitive to micro-environmental conditions controlling both pathogen growth and host immune responses. The availability of nutrients, as well as changes in oxygen, pH and interferon-γ levels, have been shown to directly influence the chlamydial life cycle and clearance. Although the lung has been traditionally regarded as a sterile environment, sequencing approaches have enabled the identification of a large number of bacteria in healthy and diseased lungs. The influence of the lung microbiota on respiratory infections has not been extensively studied so far and data on chlamydial infections are currently unavailable. In the present study, we speculate on how lung microbiota might interfere with acute and chronic infections by focusing exemplarily on the obligate intracellular C. pneumoniae. Furthermore, we consider changes in the gut microbiota as an additional player in the control of lung infections, especially in view the increasing evidence suggesting the involvement of the gut microbiota in various immunological processes throughout the human body.

Desialylation of Neisseria gonorrhoeae Lipooligosaccharide by Cervicovaginal Microbiome Sialidases: The Potential for Enhancing Infectivity in Men

Previous studies have demonstrated that Neisseria gonorrhoeae sialylates the terminal N-acetyllactosamine present on its lipooligosaccharide (LOS) by acquiring CMP-N-acetyl-5-neuraminic acid upon entering human cells during infection. This renders the organism resistant to killing by complement in normal human serum. N-acetyllactosamine residues on LOS must be free of N-acetyl-5-neuraminc acid (Neu5Ac; also known as "sialic acid") in order for organisms to bind to and enter urethral epithelial cells during infection in men. This raises the question of how the gonococcus infects men if N-acetyllactosamine residues are substituted by Neu5Ac during infection in women. Here, we demonstrate that women with gonococcal infections have levels of sialidases present in cervicovaginal secretions that can result in desialylation of (sialylated) gonococcal LOS. The principle sialidases responsible for this desialylation appear to be bacterial in origin. These studies suggest that members of the cervicovaginal microbiome can modify N. gonorrhoeae, which will enhance successful transmission to men.

The role of respiratory viruses in the etiology of bacterial pneumonia: An ecological perspective

Pneumonia is the leading cause of death among children less than 5 years old worldwide. A wide range of viral, bacterial and fungal agents can cause pneumonia: although viruses are the most common etiologic agent, the severity of clinical symptoms associated with bacterial pneumonia and increasing antibiotic resistance makes bacterial pneumonia a major public health concern. Bacterial pneumonia can follow upper respiratory viral infection and complicate lower respiratory viral infection. Secondary bacterial pneumonia is a major cause of influenza-related deaths. In this review, we evaluate the following hypotheses: (i) respiratory viruses influence the etiology of pneumonia by altering bacterial community structure in the upper respiratory tract (URT) and (ii) respiratory viruses promote or inhibit colonization of the lower respiratory tract (LRT) by certain bacterial species residing in the URT. We conducted a systematic review of the literature to examine temporal associations between respiratory viruses and bacteria and a targeted review to identify potential mechanisms of interactions. We conclude that viruses both alter the bacterial community in the URT and promote bacterial colonization of the LRT. However, it is uncertain whether changes in the URT bacterial community play a substantial role in pneumonia etiology. The exception is Streptococcus pneumoniae where a strong link between viral co-infection, increased carriage and pneumococcal pneumonia has been established.

The outcome of H. influenzae and S. pneumoniae inter-species interactions depends on pH, nutrient availability and growth phase

Haemophilus influenzae and Streptococcus pneumoniae exist together as common commensals of the healthy human nasopharynx, but both are important aetiological agents of different diseases, including the paediatric disease otitis media. It was recently shown that the formation of a multispecies biofilm of H. influenzae and S. pneumoniae is the cause of chronic forms of otitis media. However, the interactions between the two species are not clearly defined. Using a defined and kinetic analysis, our study has shown that while co-existence of the two species occurs, S. pneumoniae is also able to convert H. influenzae to a non-culturable state. We determined that this process was dependent on growth phase and pH. To analyse the H. influenzae/S. pneumoniae interactions in more depth, we investigated the growth and transcriptional profile in a pH-defined batch culture model, as well as in a growth phase independent flow cell system. Transcriptomics has shown that there are changes in gene expression in each of the species when grown in co-culture, intriguingly inducing the S. pneumoniae bacteriocin transport genes, and phage-associated genes in both species. Importantly, we have shown vast changes in gene expression in a group of S. pneumoniae metabolic genes, including those encoding lactose utilisation, glycerol utilisation and sugar transport proteins; we have shown that the expression of these genes depends not only on the presence of H. influenzae, but also on the growth system utilised.

Influenza promotes pneumococcal growth during coinfection by providing host sialylated substrates as a nutrient source

Much of the mortality attributed to influenza virus is due to secondary bacterial pneumonia, particularly from Streptococcus pneumoniae. However, mechanisms underlying this coinfection are incompletely understood. We find that prior influenza infection enhances pneumococcal colonization of the murine nasopharynx, which in turn promotes bacterial spread to the lungs. Influenza accelerates bacterial replication in vivo, and sialic acid, a major component of airway glycoconjugates, is identified as the host-derived metabolite that stimulates pneumococcal proliferation. Influenza infection increases sialic acid and sialylated mucin availability and enhances desialylation of host glycoconjugates. Pneumococcal genes for sialic acid catabolism are required for influenza to promote bacterial growth. Decreasing sialic acid availability in vivo by genetic deletion of the major airway mucin Muc5ac or mucolytic treatment limits influenza-induced pneumococcal replication. Our findings suggest that higher rates of disease during coinfection could stem from influenza-provided sialic acid, which increases pneumococcal proliferation, colonization, and aspiration.

Structural characterization of the carbohydrate-binding module of NanA sialidase, a pneumococcal virulence factor

BACKGROUND

Streptococcus pneumoniae Neuraminidase A (NanA) is a multi-domain protein anchored to the bacterial surface. Upstream of the catalytic domain of NanA is a domain that conforms to the sialic acid-recognising CBM40 family of the CAZY (carbohydrate-active enzymes) database. This domain has been identified to play a critical role in allowing the bacterium to promote adhesion and invasion of human brain microvascular endothelial cells, and hence may play a key role in promoting bacterial meningitis. In addition, the CBM40 domain has also been reported to activate host chemokines and neutrophil recruitment during infection.

RESULTS

Crystal structures of both apo- and holo- forms of the NanA CBM40 domain (residues 121 to 305), have been determined to 1.8 Å resolution. The domain shares the fold of other CBM40 domains that are associated with sialidases. When in complex with α2,3- or α2,6-sialyllactose, the domain is shown to interact only with the terminal sialic acid. Significantly, a deep acidic pocket adjacent to the sialic acid-binding site is identified, which is occupied by a lysine from a symmetry-related molecule in the crystal. This pocket is adjacent to a region that is predicted to be involved in protein-protein interactions.

CONCLUSIONS

The structural data provide the details of linkage-independent sialyllactose binding by NanA CBM40 and reveal striking surface features that may hold the key to recognition of binding partners on the host cell surface. The structure also suggests that small molecules or sialic acid analogues could be developed to fill the acidic pocket and hence provide a new therapeutic avenue against meningitis caused by S. pneumoniae.

Nasopharyngeal Bacterial Carriage in the Conjugate Vaccine Era with a Focus on Pneumococci

Seven-valent pneumococcal conjugate vaccine (PCV7) was included in the UK national immunisation program in 2006, and this was replaced by thirteen-valent PCV in 2010. During this time, the carriage of vaccine-type Streptococcus pneumoniae decreased but pneumococcal carriage remained stable due to increases in non-vaccine-type S. pneumoniae. Carriage studies have been undertaken in various countries to monitor vaccine-type replacement and to help predict the serotypes, which may cause invasive disease. There has been less focus on how conjugate vaccines indirectly affect colonization of other nasopharyngeal bacteria. If the nasopharynx is treated as a niche, then bacterial dynamics are accepted to occur. Alterations in these dynamics have been shown due to seasonal changes, antibiotic use, and sibling/day care interaction. It has been shown that, following PCV7 introduction, an eradication of pneumococcal vaccine types has resulted in increases in the abundance of other respiratory pathogens including Haemophilus influenzae and Staphylococcus aureus. These changes are difficult to attribute to PCV7 introduction alone and these studies do not account for further changes due to PCV13 implementation. This review aims to describe nasopharyngeal cocarriage of respiratory pathogens in the PCV era.

Sialic acid-mediated gene expression in Streptococcus pneumoniae and role of NanR as a transcriptional activator of the nan gene cluster

In this study, we investigated the transcriptomic response of Streptococcus pneumoniae D39 to sialic acid (N-acetylneuraminic acid [Neu5Ac]). Transcriptome comparison of wild-type D39 grown in M17 medium with and without sialic acid revealed the elevated expression of various genes and operons, including the nan gene cluster (nan operon I and nanA gene). Our microarray analysis and promoter-lacZ fusion studies showed that the transcriptional regulator NanR acts as a transcriptional activator of nan operon I and the nanA gene in the presence of sialic acid. The putative regulatory site of NanR in the promoter region of nan operon I is predicted and confirmed by promoter truncation experiments. Furthermore, the role of CcpA in the regulation of the nan gene cluster is demonstrated through microarray analysis and promoter-lacZ fusion studies, suggesting that in the presence of sialic acid and glucose, CcpA represses the expression of nan operon I while the expression of the nanA gene is CcpA independent.

Genome analysis of Flaviramulus ichthyoenteri Th78(T) in the family Flavobacteriaceae: insights into its quorum quenching property and potential roles in fish intestine

Background

Intestinal microbes play significant roles in fish and can be possibly used as probiotics in aquaculture. In our previous study, Flaviramulus ichthyoenteri Th78^T, a novel species in the family Flavobacteriaceae, was isolated from fish intestine and showed strong quorum quenching (QQ) ability. To identify the QQ enzymes in Th78^T and explore the potential roles of Th78^T in fish intestine, we sequenced the genome of Th78^T and performed extensive genomic analysis.

Results

An N-acyl homoserine lactonase FiaL belonging to the metallo-β-lactamase superfamily was identified and the QQ activity of heterologously expressed FiaL was confirmed in vitro. FiaL has relatively little similarity to the known lactonases (25.2 ~ 27.9% identity in amino acid sequence). Various digestive enzymes including alginate lyases and lipases can be produced by Th78^T, and enzymes essential for production of B vitamins such as biotin, riboflavin and folate are predicted. Genes encoding sialic acid lyases, sialidases, sulfatases and fucosidases, which contribute to utilization of mucus, are present in the genome. In addition, genes related to response to different stresses and gliding motility were also identified. Comparative genome analysis shows that Th78^T has more specific genes involved in carbohydrate transport and metabolism compared to other two isolates in Flavobacteriaceae, both isolated from sediments.

Conclusions

The genome of Th78^T exhibits evident advantages for this bacterium to survive in the fish intestine, including production of QQ enzyme, utilization of various nutrients available in the intestine as well as the ability to produce digestive enzymes and vitamins, which also provides an application prospect of Th78^T to be used as a probiotic in aquaculture.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1275-0) contains supplementary material, which is available to authorized users.

Nontypeable Haemophilus influenzae inhibits autolysis and fratricide of Streptococcus pneumoniae in vitro

Streptococcus pneumoniae (SP) and nontypeable Haemophilus influenzae (NTHi) are common commensals of the human airway and major bacterial pathogens of otitis media (OM) and other upper airway infections. The interaction between them may play an important role in the pathogenesis of polymicrobial infections. Although previous studies suggested NTHi could promote pneumococcal survival and biofilm formation, how NTHi affects pneumococcal activities has not been defined. Our data in the present studies indicated that the outcome of the interaction between SP and NTHi was in a cell-density-dependent manner and the enhancement of pneumococcal survival happened at the later stages of culturing. Using quantitative PCR, we found that the expression of pneumococcal genes regulating autolysis and fratricide, lytA and cbpD, were significantly down-regulated in co-culture with NTHi. We further observed that influence of NTHi was not on direct cell-to-cell contact, but that this contact may contribute to the interaction between these two microorganisms. These results suggest that pneumococcal survival and biofilm formation can be enhanced by down-regulating pneumococcal cell wall hydrolase production thereby inhibiting pneumococcal autolysis and fratricide in the presence of NTHi.

Hyaluronic acid derived from other streptococci supports Streptococcus pneumoniae in vitro biofilm formation

We investigate the role of hyaluronic acid (HA) on S. pneumoniae in vitro biofilm formation and evaluate gene expressions of virulence and/or biofilm related genes. Biofilms were grown in medium supplied with HA derived from capsule of Streptococcus equi. The biomasses of biofilms were detected by crystal-violet (CV) microtiter plate assay, and the morphology was viewed under scanning electron microscope (SEM). The gene expressions were assessed by relative quantitative RT-PCR. The results showed that the HA support pneumococcal growth in planktonic form and within biofilms. The CV-microtiter plate assay detected significantly increased biofilm growth in medium containing HA. The SEM analysis revealed thick and organized biofilms in positive control and HA supplemented medium. The nanA, nanB, bgaA, strH, luxS, hysA, ugl, and PST-EIIA encoding genes were significantly upregulated in the planktonic cells grown in presence of HA, while the lytA and comA genes were downregulated. Similarly the luxS, hysA, ugl, and PST-EIIA encoding genes were significantly upregulated by more than 2-folds in HA biofilms. The results of this study indicate that the HA derived from capsule of S. equi supports pneumococcal growth in planktonic state and within biofilms and upregulated virulence and biofilm related genes.

Haemophilus influenzae and Streptococcus pneumoniae: living together in a biofilm

Streptococcus pneumoniae and Haemophilus influenzae are both commensals of the human nasopharynx with an ability to migrate to other niches within the human body to cause various diseases of the upper respiratory tract such as pneumonia, otitis media and bronchitis. They have long been detected together in a multispecies biofilm in infected tissue. However, an understanding of their interplay is a recent field of study, and while over recent years, there has been research that has identified many specific elements important in these biofilms, to date, it remains questionable whether the relationship between H. influenzae and S. pneumoniae is competitive or cooperative. Additionally, the factors that govern the nature of the interspecies interaction are still undefined. This review aims to collate the information that has emerged on the cocolonization and co-infection by S. pneumoniae and nontypeable H. influenzae (NTHi) and their formation of a multispecies biofilm.

Nasopharyngeal bacterial interactions in children

TOC summary: Pathogen prevalence differs during periods of health and at onset of acute otitis media.

Viral and bacterial interactions in the upper respiratory tract

Respiratory infectious diseases are mainly caused by viruses or bacteria that often interact with one another. Although their presence is a prerequisite for subsequent infections, viruses and bacteria may be present in the nasopharynx without causing any respiratory symptoms. The upper respiratory tract hosts a vast range of commensals and potential pathogenic bacteria, which form a complex microbial community. This community is assumed to be constantly subject to synergistic and competitive interspecies interactions. Disturbances in the equilibrium, for instance due to the acquisition of new bacteria or viruses, may lead to overgrowth and invasion. A better understanding of the dynamics between commensals and pathogens in the upper respiratory tract may provide better insight into the pathogenesis of respiratory diseases. Here we review the current knowledge regarding specific bacterial–bacterial and viral–bacterial interactions that occur in the upper respiratory niche, and discuss mechanisms by which these interactions might be mediated. Finally, we propose a theoretical model to summarize and illustrate these mechanisms.

Density interactions among Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus in the nasopharynx of young Peruvian children

Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus are commonly carried in the nasopharynx of young children, and have been speculated to interact with each other. Although earlier studies used cultures alone to assess these interactions, the addition of real-time quantitative polymerase chain reaction (qPCR) provides further insight into these interactions. We compared results of culture and qPCR for the detection of these 3 bacteria in 446 nasopharynx samples collected from 360 healthy young children in a prospective cohort study in the Peruvian Andes. Patterns of concurrent bacterial colonization were studied using repeated measures logistic regression models with generalized estimating equations. Spearman correlation coefficients were used to assess correlations among bacterial densities. At a bacterial density <10 colony forming units/mL measured by qPCR, culture detected significantly less carriers (P < 0.0001) for all 3 pathogens, than at a bacterial density >10 colony forming units/mL. In addition, there was a positive association between S. pneumoniae and H. influenzae colonization measured by both culture (odds ratio [OR] 3.11-3.17, P < 0.001) and qPCR (OR 1.95-1.97, P < 0.01). The densities of S. pneumoniae and H. influenzae, measured by qPCR, were positively correlated (correlation coefficient 0.32, P < 0.001). A negative association was found between the presence of S. pneumoniae and Staphylococcus aureus in carriage with both culture (OR 0.45, P = 0.024) and qPCR (OR 0.61, P < 0.05). The impact of density on detection by culture and the observed density-related interactions support use of qPCR in additional studies to examine vaccine effects on diverse bacterial species.

Pneumococcal carbohydrate transport: food for thought

Streptococcus pneumoniae relies exclusively on carbohydrates as a carbon source and devotes 30% of all transport mechanisms to carbohydrate import. Pneumococci utilize at least 32 carbohydrates in vitro. However, some proposed substrates are not human-derived, so it is unclear where they are encountered in the host niche, and other substrates remain unidentified. The majority of transporter loci are conserved, arguing against redundancy and instead for distinct roles during pathogenesis. Despite this, expression and regulation of carbohydrate transporters in vivo remain ill defined. Recent work has also demonstrated that multiple ABC transporters share an ATPase; whether this evolved for genome minimization or for transporter regulation remains unknown. Continued efforts to understand carbohydrate import may reveal novel vaccine and therapeutic targets and increase our understanding of pneumococcal pathogenesis.

Co-infection subverts mucosal immunity in the upper respiratory tract

Polymicrobial interactions on mucosal surfaces can influence inflammation, immunity, and disease outcome. Here, we review how host responses to colonization in the upper respiratory tract with the bacterial pathogen Streptococcus pneumoniae can be altered by co-infection. Recent advances provide a mechanistic understanding of how mucosal immunity can be subverted at distinct immunological time-points during pneumococcal colonization by other pathogens such as Haemophilus influenzae, influenza type A and Staphylococcus aureus. These examples use animal models of co-infection to highlight how otherwise effective host responses can be rendered ineffective by co-infection, and vice versa. The complex microbial ecology of mucosal sites must be considered to fully understand how immune responses in a natural setting influence the outcome of host-pathogen interactions.

Streptococcus pneumoniae can utilize multiple sources of hyaluronic acid for growth

The mechanisms by which Streptococcus pneumoniae obtains carbohydrates for growth during airway colonization remain to be elucidated. The low concentration of free carbohydrates in the normal human airway suggests that pneumococci must utilize complex glycan structures for growth. The glycosaminoglycan hyaluronic acid is present on the apical surface of airway epithelial cells. As pneumococci express a hyaluronate lyase (Hyl) that cleaves hyaluronic acid into disaccharides, we hypothesized that during colonization pneumococci utilize the released carbohydrates for growth. Hyaluronic acid supported significant pneumococcal growth in an hyl-dependent manner. A phosphoenolpyruvate-dependent phosphotransferase system (PTS) and an unsaturated glucuronyl hydrolase (Ugl) encoded downstream of hyl are also essential for growth on hyaluronic acid. This genomic arrangement is present in several other organisms, suggesting conservation of the utilization mechanism between species. In vivo experiments support the hypothesis that S. pneumoniae utilizes hyaluronic acid as a carbon source during colonization. We also demonstrate that pneumococci can utilize the hyaluronic acid capsule of other bacterial species for growth, suggesting an alternative carbohydrate source for pneumococcal growth. Together, these data support a novel function for pneumococcal degradation of hyaluronic acid in vivo and provide mechanistic details of growth on this glycosaminoglycan.

Bacterial interactions in the nasopharynx - effects of host factors in children attending day-care centers

The nasopharynges of preschool children are often colonized by potentially pathogenic bacteria. The interactions between these common pathogens and certain host factors were investigated in healthy preschool children 1-6 years of age. Nasopharynx samples were collected from all 63 children attending a day-care center that experienced an outbreak of penicillin-resistant Streptococcus pneumoniae. The samples were analyzed for S. pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Group A Streptococci. A model for the risk of carrying these bacteria was established using logistic regression. S. pneumoniae and H. influenzae antagonize each other, whereas M. catarrhalis and S. pneumoniae have a positively association. The risk of carrying M. catarrhalis decreases with age. The time spent in day care each week was not shown to influence the rate of carriage of any of these pathogens. The negative effect of H. influenzae on S. pneumoniae is discussed in relation to the carriage of penicillin-resistant S. pneumoniae, and possible mechanisms involved in this interaction are presented.

Sialic acid, periodontal pathogens and Tannerella forsythia: stick around and enjoy the feast!

Periodontal pathogens, like any other human commensal or pathogenic bacterium, must possess both the ability to acquire the necessary growth factors and the means to adhere to surfaces or reside and survive in their environmental niche. Recent evidence has suggested that sialic acid containing host molecules may provide both of these requirements in vivo for several periodontal pathogens but most notably for the red complex organism Tannerella forsythia. Several other periodontal pathogens also possess sialic acid scavenging enzymes - sialidases, which can also expose adhesive epitopes, but might also act as adhesins in their own right. In addition, recent experimental work coupled with the release of several genome sequences has revealed that periodontal bacteria have a range of sialic acid uptake and utilization systems while others may also use sialic acid as a cloaking device on their surface to mimic host and avoid immune recognition. This review will focus on these systems in a range of periodontal bacteria with a focus on Ta. forsythia.

Leukocyte inflammatory responses provoked by pneumococcal sialidase

Cell surface expression of sialic acid has been reported to decrease during immune cell activation, but the significance and regulation of this phenomenon are still being investigated. The major human bacterial pathogen Streptococcus pneumoniae causes pneumonia, sepsis and meningitis, often accompanied by strong inflammatory responses. S. pneumoniae expresses a sialidase (NanA) that contributes to mucosal colonization, platelet clearance, and blood-brain barrier penetration. Using wild-type and isogenic NanA-deficient mutant strains, we showed that S. pneumoniae NanA can desialylate the surface of human THP-1 monocytes, leading to increased ERK phosphorylation, NF-κB activation, and proinflammatory cytokine release. S. pneumoniae NanA expression also stimulates interleukin-8 release and extracellular trap formation from human neutrophils. A mechanistic contribution of unmasking of inhibitory Siglec-5 from cis sialic acid interactions to the proinflammatory effect of NanA is suggested by decreased SHP-2 recruitment to the Siglec-5 intracellular domain and RNA interference studies. Finally, NanA increased production of proinflammatory cytokines in a murine intranasal challenge model of S. pneumoniae pneumonia.

Importance Sialic acids decorate the surface of all mammalian cells and play important roles in physiology, development, and evolution. Siglecs are sialic acid-binding receptors on the surface of immune cells, many of which engage in cis interactions with host sialoglycan ligands and dampen inflammatory responses through transduction of inhibitory signals. Recently, certain bacterial pathogens have been shown to suppress leukocyte innate immune responses by molecular mimicry of host sialic acid structures and engagement of inhibitory Siglecs. Our present work shows that the converse can be true, i.e., that a microbial sialic acid-cleaving enzyme can induce proinflammatory responses, which are in part mediated by unmasking of an inhibitory Siglec. We conclude that host leukocytes are poised to detect and respond to microbial sialidase activity with exaggerated inflammatory responses, which could be beneficial or detrimental to the host depending on the site, stage and magnitude of infection.

Sialic acids decorate the surface of all mammalian cells and play important roles in physiology, development, and evolution. Siglecs are sialic acid-binding receptors on the surface of immune cells, many of which engage in cis interactions with host sialoglycan ligands and dampen inflammatory responses through transduction of inhibitory signals. Recently, certain bacterial pathogens have been shown to suppress leukocyte innate immune responses by molecular mimicry of host sialic acid structures and engagement of inhibitory Siglecs. Our present work shows that the converse can be true, i.e., that a microbial sialic acid-cleaving enzyme can induce proinflammatory responses, which are in part mediated by unmasking of an inhibitory Siglec. We conclude that host leukocytes are poised to detect and respond to microbial sialidase activity with exaggerated inflammatory responses, which could be beneficial or detrimental to the host depending on the site, stage and magnitude of infection.

Exposure of Thomsen-Friedenreich antigen in Streptococcus pneumoniae infection is dependent on pneumococcal neuraminidase A

Pneumococcal hemolytic uremic syndrome is recognized in a small portion of otherwise healthy children who have or have recently had Streptococcus pneumoniae infections, including severe pneumonia, meningitis, and bacteremia. As in other types of hemolytic uremic syndrome (HUS), pneumococcal HUS is characterized by microangiopathic hemolytic anemia, and thrombocytopenia, usually with extensive kidney damage. Although not demonstrated in vivo, the pathogenesis of pneumococcal HUS has been attributed to the action pneumococcal neuraminidase exposing the usually cryptic Thomsen-Friedenreich antigen (T-antigen) on red blood cells (RBC), and kidney glomeruli. We evaluated the effect of pneumococcal infection on desialylation of RBC and glomeruli during pneumococcal infections in mice. Following intravenous infection with capsular type 19F pneumococci, CFU levels exceeding 1000 CFU/mL blood by the third day were significantly more likely to result in exposed T-antigen on RBC than lower levels of bacteremia. In a pneumonia model, significantly more T-antigen was exposed on RBC in mice treated with penicillin than in those receiving mock treatment. Utilizing mutant pneumococci, we demonstrated that neuraminidase A but not neuraminidase B was necessary for exposure of T-antigen on RBC in vivo. Thus, pneumococcal neuraminidase A is necessary for the exposure of T-antigen in vivo and treatment with penicillin increases this effect. Interestingly, NanA(-) pneumococci were found in the blood in higher numbers and caused more deaths than wild type, NanB(-), or the NanA(-)/NanB(-) pneumococci.