Biofilm and planktonic pneumococci demonstrate disparate immunoreactivity to human convalescent sera

Protective Efficacy of Novel Oral Biofilm Vaccines against Lactococcus garvieae Infection in Mullet, Mugil cephalus

Lactococcus garvieae (L. garvieae) is an important pathogen that causes enormous economic losses in both marine and freshwater aquaculture. At present, antibiotics are the only option for farmers to reduce the losses caused by L. garvieae. However, the usage of antibiotics leads to environmental pollution and the production of drug-resistant strains of bacteria. Therefore, vaccination is preferred as an alternative method to prevent infectious diseases. In this study, we describe an effective approach to the production of an oral biofilm vaccine, using bacteria grown on chitosan particles to form biofilms, and thus providing an inactive pathogen that enhances the immune response in fish. We observed the formation of a biofilm on chitosan particles and administered the novel oral biofilm vaccine to fish. We analyzed the immune responses, including antibody production, phagocytic ability, albumin/globulin ratio and immune-related genes, of vaccinated and control groups of black mullet. Our results show that the phagocytic ability of the biofilm vaccine group was 84%, which is significantly higher than that of the control group, and the antibody production in this group was significantly higher compared with the other group. The mRNA expression levels of immune-related genes (TLR2, IL-1β, TNF-α) were significantly upregulated in the spleen after vaccination. In challenge experiments, the relative percent survival (RPS) was 77% in the biofilm vaccine group, 18% in the whole-cell vaccine group, and 0% in the chitosan particle group at 32 days post-vaccination. In addition, we also found that the relative percent survival (RPS) at 1 day post-vaccination was 74% in the biofilm vaccine group, 42% in the whole-cell vaccine group, and 26% in the chitosan particle group. In both long-term and short-term challenge experiments, the viability of the biofilm vaccine group was significantly higher than that of the whole-cell, chitosan particle and PBS groups. We conclude that based on its protective effect, the L. garvieae biofilm vaccine is better than the whole-cell vaccine when challenged several weeks after vaccination. In addition, the biofilm vaccine also has a greater protective effect than the whole-cell vaccine when challenged immediately after vaccination. Therefore, the biofilm vaccine might represent a novel method for the prevention and treatment of L. garvieae infection.

The serine protease HtrA plays a key role in heat-induced dispersal of pneumococcal biofilms

Streptococcus pneumoniae (the pneumococcus) colonizes the human nasopharynx by forming multicellular biofilms. Due to the high level of asymptomatic carriage, transition to infections, such as otitis media, pneumonia, sepsis, and meningitis, occurs often enough that the pneumococcus remains a major cause of disease and death globally. Virus infection and virus-induced responses, such as increased temperature (fever), trigger release of virulent bacteria from colonizing biofilms. The exact mechanisms involved in pneumococcal egress during biofilm dispersal remain unknown, although we hypothesize that disruption of the biofilm matrix encasing the bacteria is necessary. Here, we utilized established in vitro biofilm dispersal models to investigate the involvement of proteases in bacterial egress from pneumococcal biofilms. We demonstrate the importance of protease activity, both through increased bacterial release following addition of proteases and reduced heat-induced biofilm dispersal in the presence of protease inhibitors. We identify a key role for the surface-exposed serine protease HtrA, but not PrtA, in heat-induced biofilm dispersal. Bacterial release from htrA-negative biofilms was significantly reduced compared to wild-type isogenic strains but was restored and increased above wild-type levels following addition of recombinant HtrA. Understanding the specific mechanisms involved in bacterial egress may provide novel targets for future strategies aimed to specifically interfere with disease progression without disturbing nasopharyngeal biofilm colonization.

Selection of DNA aptamers to Streptococcus pneumonia and fabrication of graphene oxide based fluorescent assay

Pneumococci are one of the leading causes of infections throughout the world causing problems mainly in children, elderly, and immune-deficient patients. In recent years antibiotic resistant Streptococcus pneumoniae strains become widespread. Therefore simple, rapid, and specific detection methods are needed for public health. In this study, DNA aptamer probes against S. pneumoniae were selected using bacterial Systematic Evolution of Ligands by Exponential Enrichment (SELEX) and these probes were integrated in to a graphene oxide (GO) based fluorescent assay. Among the tested aptamers three candidates Lyd-1, Lyd-2 and Lyd-3 showed K_d values of 844.7 ± 123.6, 1984.8 ± 347.5, and 661.8 ± 111.3 nM, respectively. These candidates showed binding affinity to S. pneumoniae and no specific binding to the bacteria used in negative selection. The binding of aptamers were showed by fluorescence spectroscopy and flow cytometry. GO based label-free fluorescent assay developed using Lyd-3 aptamer had a unique detection limit of 15 cfu mL^-1. Thus we believe that the selected aptamers and fabricated GO based assay has potential to be used in the detection of S. pneumoniae. Selected aptamers selectively bind to S. pneumonia with anti-pneumococcal potential and holds great potential to be used as molecular probes for identifying and targeting.

The LuxS/AI-2 Quorum-Sensing System of Streptococcus pneumoniae Is Required to Cause Disease, and to Regulate Virulence- and Metabolism-Related Genes in a Rat Model of Middle Ear Infection

Objective:Streptococcus pneumoniae colonizes the nasopharynx of children, and from nasopharynx it could migrate to the middle ear and causes acute otitis media (AOM). During colonization and AOM, the pneumococcus forms biofilms. In vitro biofilm formation requires a functional LuxS/AI-2 quorum-sensing system. We investigated the role of LuxS/AI-2 signaling in pneumococcal middle ear infection, and identified the genes that are regulated by LuxS/AI-2 during pneumococcal biofilm formation.

Methods:Streptococcus pneumoniae D39 wild-type and an isogenic D39ΔluxS strain were utilized to evaluate in vitro biofilm formation, and in vivo colonization and epithelial damage using a microtiter plate assay and a rat model of pneumococcal middle ear infection, respectively. Biofilm structures and colonization and epithelial damage were evaluated at the ultrastructural level by scanning electron microscopy and confocal microscopy. Microarrays were used to investigate the global genes that were regulated by LuxS/AI-2 during biofilm formation.

Results: The biofilm biomass and density of D39ΔluxS were significantly (p < 0.05) lower than those of D39 wild-type. SEM and confocal microscopy revealed that D39ΔluxS formed thin biofilms in vitro compared with D39 wild-type. The in vivo model of middle ear infection showed that D39ΔluxS resulted in ~60% less (p < 0.05) bacterial colonization than the wild-type. SEM analysis of the rat middle ears revealed dense biofilm-like cell debris deposited on the cilia in wild-type D39-infected rats. However, little cell debris was deposited in the middle ears of the D39ΔluxS-inoculated rats, and the cilia were visible. cDNA-microarray analysis revealed 117 differentially expressed genes in D39ΔluxS compared with D39 wild-type. Among the 66 genes encoding putative proteins and previously characterized proteins, 60 were significantly downregulated, whereas 6 were upregulated. Functional annotation revealed that genes involved in DNA replication and repair, ATP synthesis, capsule biosynthesis, cell division, the cell cycle, signal transduction, transcription regulation, competence, virulence, and carbohydrate metabolism were downregulated in the absence of LuxS/AI-2.

Conclusion: The S. pneumoniae LuxS/AI-2 quorum-sensing system is necessary for biofilm formation and the colonization of the ear epithelium, and caused middle ear infection in the rat model. LuxS/AI-2 regulates the expression of the genes involved in virulence and bacterial fitness during pneumococcal biofilm formation.

Current therapies in treatment and prevention of fracture wound biofilms: why a multifaceted approach is essential for resolving persistent infections

Traumatic orthopedic injuries, particularly extremity wounds, are a significant cause of morbidity. Despite prophylactic antibiotic treatment and surgical intervention, persistent infectious complications can and do occur. Persistent bacterial infections are often caused by biofilms, communities of antibiotic tolerant bacteria encased within a matrix. The structural and metabolic differences in this mode of growth make treatment difficult. Herein, we describe both established and novel, experimental treatments targeted at various stages of wound healing that are specifically aimed at reducing and eliminating biofilm bacteria. Importantly, the highly tolerant nature of these bacterial communities suggests that most singular approaches could be circumvented and a multifaceted, combinatorial approach will be the most effective strategy for treating these complicated infections.

Differential Immunoreactivity to Bovine Convalescent Serum Between Mycoplasma bovis Biofilms and Planktonic Cells Revealed by Comparative Immunoproteomic Analysis

Mycoplasma bovis is a major bovine pathogen that causes considerable economic losses in the cattle industry worldwide. Moreover, M. bovis biofilm can persist in the environment and its host. To date, M. bovis biofilm antigens recognized by bovine convalescent sera and their comparison with planktonic cells have not yet been explored. This study utilized an immunoproteomic approach using two-dimensional electrophoresis, immunoblotting using convalescent bovine serum, and subsequent matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS) to identify the immunoreactive proteins expressed in biofilm- and planktonic-grown M. bovis strain 08M. Results showed that M. bovis biofilms and planktonic cells demonstrate differential immunoreactivity to bovine convalescent serum for the first time. A total of 10 and 8 immunoreactive proteins were identified for biofilms and planktonic cells, respectively. To our knowledge, a total of 12 out of 15 had not been reported as immunoreactive proteins in M. bovis, and six were specific to M. bovis biofilms. Three proteins, namely, endoglucanase, thiol peroxidase, and one putative membrane protein, that is, mycoplasma immunogenic lipase A, were identified in planktonic cells and biofilms. Most of the identified proteins were cytoplasmic proteins that were mainly involved in transport and metabolism. Moreover, ATP binding, oxidoreductase activity, and GTP binding were their most representative molecular functions. DnaK and Tuf appeared to be the most interactive immunoreactive agent among the identified proteins. Furthermore, six proteins had potential as serodiagnostic antigens. These data will be helpful to improve our current understanding on the host response to M. bovis biofilms and planktonic cells, which may facilitate the development of novel molecular candidates of improved diagnostics and vaccines to prevent M. bovis infections.

Streptococcus pneumoniae Modulates Staphylococcus aureus Biofilm Dispersion and the Transition from Colonization to Invasive Disease

Streptococcus pneumoniae and Staphylococcus aureus are ubiquitous upper respiratory opportunistic pathogens. Individually, these Gram-positive microbes are two of the most common causative agents of secondary bacterial pneumonia following influenza A virus infection, and they constitute a significant source of morbidity and mortality. Since the introduction of the pneumococcal conjugate vaccine, rates of cocolonization with both of these bacterial species have increased, despite the traditional view that they are antagonistic and mutually exclusive. The interactions between S. pneumoniae and S. aureus in the context of colonization and the transition to invasive disease have not been characterized. In this report, we show that S. pneumoniae and S. aureus form stable dual-species biofilms on epithelial cells in vitro. When these biofilms are exposed to physiological changes associated with viral infection, S. pneumoniae disperses from the biofilm, whereas S. aureus dispersal is inhibited. These findings were supported by results of an in vivo study in which we used a novel mouse cocolonization model. In these experiments, mice cocolonized in the nares with both bacterial species were subsequently infected with influenza A virus. The coinfected mice almost exclusively developed pneumococcal pneumonia. These results indicate that despite our previous report that S. aureus disseminates into the lungs of mice stably colonized with these bacteria following influenza A virus infection, cocolonization with S. pneumoniae in vitro and in vivo inhibits S. aureus dispersal and transition to disease. This study provides novel insight into both the interactions between S. pneumoniae and S. aureus during carriage and the transition from colonization to secondary bacterial pneumonia.

In this study, we demonstrate that Streptococcus pneumoniae can modulate the pathogenic potential of Staphylococcus aureus in a model of secondary bacterial pneumonia. We report that host physiological signals related to viral infection cease to elicit a dispersal response from S. aureus while in a dual-species setting with S. pneumoniae, in direct contrast to results of previous studies with each species individually. This study underscores the importance of studying polymicrobial communities and their implications in disease states.

A novel streptococcal cell-cell communication peptide promotes pneumococcal virulence and biofilm formation

Streptococcus pneumoniae (pneumococcus) is a major human pathogen. It is a common colonizer of the human respiratory track, where it utilizes cell-cell communication systems to coordinate population-level behaviors. We reasoned that secreted peptides that are highly expressed during infection are pivotal for virulence. Thus, we used in silico pattern searches to define a pneumococcal secretome and analyzed the transcriptome of the clinically important PMEN1 lineage to identify which peptide-encoding genes are highly expressed in vivo. In this study, we characterized virulence peptide 1 (vp1), a highly expressed Gly-Gly peptide-encoding gene in chinchilla middle ear effusions. The vp1 gene is widely distributed across pneumococcus as well as encoded in related species. Studies in the chinchilla model of middle ear infection demonstrated that VP1 is a virulence determinant. The vp1 gene is positively regulated by a transcription factor from the Rgg family and its cognate SHP (short hydrophobic peptide). In vitro data indicated that VP1 promotes increased thickness and biomass for biofilms grown on chinchilla middle ear epithelial cells. Furthermore, the wild-type biofilm is restored with the exogenous addition of synthetic VP1. We conclude that VP1 is a novel streptococcal regulatory peptide that controls biofilm development and pneumococcal pathogenesis.

Proteomic variation and diversity in clinical Streptococcus pneumoniae isolates from invasive and non-invasive sites

Streptococcus pneumoniae is responsible for a variety of invasive and non-invasive human infections. There are over 90 serotypes of S. pneumoniae differing in their ability to adapt to the different niches within the host. Two-dimensional gel electrophoresis was used to discriminate clinical S. pneumoniae isolates recovered from either blood cultures (invasive site isolates) or other sites, including sputum, tracheal aspirate, ear, eye and skin swabs (non-invasive site isolates). Global protein expression profiles for five invasive site and six non-invasive site isolates representing five different serotypes (serotypes 4, 6, 9, 14 and 23) were obtained for each isolate and combined into a single data set using Progenesis SameSpots^™ software. One-hundred and eighty six protein spots (39% of the protein spots in the dataset) differed significantly (ANOVA, p<0.05) in abundance between the invasive site (101 upregulated protein spots) and non-invasive site (85 upregulated protein spots) isolates. Correlations between the bacterial proteomes and their sites of isolation were determined by Principal Component Analysis (PCA) using the significantly different protein spots. Out of the 186 variable protein spots, 105 exhibited a serotype-associated pattern of variability. The expression of the remaining 81 protein spots was concluded to be uniquely linked to the site of bacterial isolation. Mass spectrometry was used to identify selected protein spots that showed either constant or differential abundance levels. The identified proteins had a diverse range of functions including, capsule biogenesis, DNA repair, protein deglycation, translation, stress response and virulence as well as amino acid, carbohydrate, lipid and nucleotide metabolism. These findings provide insight on the proteins that contribute towards the adaptation of the bacteria to different sites within the host.

The Role of the Microbiota in Shaping Infectious Immunity

Humans are meta-organisms that maintain a diverse population of microorganisms on their barrier surfaces, collectively named the microbiota. Since most pathogens either cross or inhabit barrier surfaces, the microbiota plays a critical and often protective role during infections, both by modulating immune system responses and by mediating colonization resistance. However, the microbiota can also act as a reservoir for opportunistic microorganisms that can 'bloom', significantly complicating diseases of barrier surfaces by contributing to inflammatory immune responses. This review discusses our current understanding of the complex interactions between the host, its microbiota, and pathogenic organisms, focusing in particular on the intestinal mucosa.

Streptococcus pneumoniae proteomics: determinants of pathogenesis and vaccine development

Streptococcus pneumoniae is a major pathogen that is responsible for a variety of invasive diseases. The bacteria gain entry initially by establishing a carriage state in the nasopharynx from where they migrate to other sites in the body. The worldwide distribution of the bacteria and the severity of the diseases have led to a significant level of interest in the development of vaccines against the bacteria. Current vaccines, based on the bacterial polysaccharide, have a number of limitations including poor immunogenicity and limited effectiveness against all pneumococcal serotypes. There are many challenges in developing vaccines that will be effective against the diverse range of isolates and serotypes for this highly variable bacterial pathogen. This review considers how proteomic technologies have extended our understanding of the pathogenic mechanisms of nasopharyngeal colonization and disease development as well as the critical areas in developing protein-based vaccines.

Comparative proteomic analysis of biofilm and planktonic cells of Lactobacillus plantarum DB200

This study investigated the relative abundance of extracellular and cell wall associated proteins (exoproteome), cytoplasmic proteins (proteome), and related phenotypic traits of Lactobacillus plantarum grown under planktonic and biofilm conditions. Lactobacillus plantarum DB200 was preliminarily selected due to its ability to form biofilms and to adhere to Caco2 cells. As shown by fluorescence microscope analysis, biofilm cells became longer and autoaggregated at higher levels than planktonic cells. The molar ratio between glucose consumed and lactate synthesised was markedly decreased under biofilm compared to planktonic conditions. DIGE analysis showed a differential exoproteome (115 protein spots) and proteome (44) between planktonic and biofilm L. plantarum DB200 cells. Proteins up- or downregulated by at least twofold (p < 0.05) were found to belong mainly to the following functional categories: cell wall and catabolic process, cell cycle and adhesion, transport, glycolysis and carbohydrate metabolism, exopolysaccharide metabolism, amino acid and protein metabolisms, fatty acid and lipid biosynthesis, purine and nucleotide metabolism, stress response, oxidation/reduction process, and energy metabolism. Many of the above proteins showed moonlighting behavior. In accordance with the high expression levels of stress proteins (e.g., DnaK, GroEL, ClpP, GroES, and catalase), biofilm cells demonstrated enhanced survival under conditions of environmental stress.

An immunoproteomic approach for characterization of dormancy within Staphylococcus epidermidis biofilms

Virulence of Staphylococcus epidermidis is mainly attributed to surface colonization and biofilm formation in indwelling medical devices. Physiological heterogeneity of biofilms may influence host immune response and sensitivity to antibiotics. Dormant cells, among others, contribute to biofilm heterogeneity. The aim of this study was to identify immunogenic proteins of S. epidermidis biofilms associated with dormancy mechanism, by using two-dimensional electrophoresis (2-DE) immunoblotting and mass spectrometry (MS). A total of 19 bacterial proteins, recognized by human serum samples, were identified. These proteins were mainly involved in small molecule metabolic biological processes. Catalytic activity and ion binding were the most representative molecular functions. CodY and GpmA proteins were more reactive to sera when biofilm dormancy was induced, while FtnA and ClpP were more reactive when dormancy was prevented. This is the first work that identifies differences in immunoreactive proteins within bacterial biofilms with induced or prevented dormancy. Considering the importance of dormancy within biofilms, further evaluation of these proteins can provide insights into the mechanisms related to dormancy and help to improve current understanding on how dormancy affects the host immune response.

Streptococcus pneumoniae biofilm formation and dispersion during colonization and disease

Streptococcus pneumoniae (the pneumococcus) is a common colonizer of the human nasopharynx. Despite a low rate of invasive disease, the high prevalence of colonization results in millions of infections and over one million deaths per year, mostly in individuals under the age of 5 and the elderly. Colonizing pneumococci form well-organized biofilm communities in the nasopharyngeal environment, but the specific role of biofilms and their interaction with the host during colonization and disease is not yet clear. Pneumococci in biofilms are highly resistant to antimicrobial agents and this phenotype can be recapitulated when pneumococci are grown on respiratory epithelial cells under conditions found in the nasopharyngeal environment. Pneumococcal biofilms display lower levels of virulence in vivo and provide an optimal environment for increased genetic exchange both in vitro and in vivo, with increased natural transformation seen during co-colonization with multiple strains. Biofilms have also been detected on mucosal surfaces during pneumonia and middle ear infection, although the role of these biofilms in the disease process is debated. Recent studies have shown that changes in the nasopharyngeal environment caused by concomitant virus infection, changes in the microflora, inflammation, or other host assaults trigger active release of pneumococci from biofilms. These dispersed bacteria have distinct phenotypic properties and transcriptional profiles different from both biofilm and broth-grown, planktonic bacteria, resulting in a significantly increased virulence in vivo. In this review we discuss the properties of pneumococcal biofilms, the role of biofilm formation during pneumococcal colonization, including their propensity for increased ability to exchange genetic material, as well as mechanisms involved in transition from asymptomatic biofilm colonization to dissemination and disease of otherwise sterile sites. Greater understanding of pneumococcal biofilm formation and dispersion will elucidate novel avenues to interfere with the spread of antibiotic resistance and vaccine escape, as well as novel strategies to target the mechanisms involved in induction of pneumococcal disease.

Promises and pitfalls of live attenuated pneumococcal vaccines

The pneumococcus is a remarkably adaptable pathogen whose disease manifestations range from mucosal surface infections such as acute otitis media and pneumonia to invasive infections such as sepsis and meningitis. Currently approved vaccines target the polysaccharide capsule, of which there are over 90 distinct serotypes, leading to rapid serotype replacement in vaccinated populations. Substantial progress has been made in the development of a universal pneumococcal vaccine, with efforts focused on broadly conserved and protective protein antigens. An area attracting considerable attention is the potential application of live attenuated vaccines to confer serotype-independent protection against mucosal and systemic infection. On the basis of recent work to understand the mucosal and systemic responses to nasal administration of pneumococci and to develop novel attenuation strategies, the prospect of a practical and protective live vaccine remains promising.

Pneumococci in biofilms are non-invasive: implications on nasopharyngeal colonization

Streptococcus pneumoniae (the pneumococcus) is an opportunistic pathogen that colonizes the human nasopharynx asymptomatically. Invasive pneumococcal disease develops following bacterial aspiration into the lungs. Pneumococci within the nasopharynx exist as biofilms, a growth phenotype characterized by surface attachment, encasement within an extracellular matrix, and antimicrobial resistance. Experimental evidence indicates that biofilm pneumococci are attenuated vs. their planktonic counterpart. Biofilm pneumococci failed to cause invasive disease in experimentally challenged mice and in vitro were shown to be non-invasive despite being hyper-adhesive. This attenuated phenotype corresponds with observations that biofilm pneumococci elicit significantly less cytokine and chemokine production from host cells than their planktonic counterparts. Microarray and proteomic studies show that pneumococci within biofilms have decreased metabolism, less capsular polysaccharide, and reduced production of the pore-forming toxin pneumolysin. Biofilm pneumococci are predominately in the transparent phenotype, which has elevated cell wall phosphorylcholine, an adhesin subject to C-reactive protein mediated opsonization. Herein, we review these changes in virulence, interpret their impact on colonization and transmission, and discuss the notion that non-invasive biofilms are principal lifestyle of S. pneumoniae.

Pronounced metabolic changes in adaptation to biofilm growth by Streptococcus pneumoniae

Streptococcus pneumoniae accounts for a significant global burden of morbidity and mortality and biofilm development is increasingly recognised as important for colonization and infection. Analysis of protein expression patterns during biofilm development may therefore provide valuable insights to the understanding of pneumococcal persistence strategies and to improve vaccines. iTRAQ (isobaric tagging for relative and absolute quantification), a high-throughput gel-free proteomic approach which allows high resolution quantitative comparisons of protein profiles between multiple phenotypes, was used to interrogate planktonic and biofilm growth in a clinical serotype 14 strain. Comparative analyses of protein expression between log-phase planktonic and 1-day and 7-day biofilm cultures representing nascent and late phase biofilm growth were carried out. Overall, 244 proteins were identified, of which >80% were differentially expressed during biofilm development. Quantitatively and qualitatively, metabolic regulation appeared to play a central role in the adaptation from the planktonic to biofilm phenotype. Pneumococci adapted to biofilm growth by decreasing enzymes involved in the glycolytic pathway, as well as proteins involved in translation, transcription, and virulence. In contrast, proteins with a role in pyruvate, carbohydrate, and arginine metabolism were significantly increased during biofilm development. Downregulation of glycolytic and translational proteins suggests that pneumococcus adopts a covert phenotype whilst adapting to an adherent lifestyle, while utilization of alternative metabolic pathways highlights the resourcefulness of pneumococcus to facilitate survival in diverse environmental conditions. These metabolic proteins, conserved across both the planktonic and biofilm phenotypes, may also represent target candidates for future vaccine development and treatment strategies. Data are available via ProteomeXchange with identifier PXD001182.

The case for involvement of spiroplasma in the pathogenesis of transmissible spongiform encephalopathies

Spiroplasma biofilm formation explains the role of these wall-less bacteria in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Spiroplasma embedded in the biofilm polysaccharide matrix are markedly resistant to physical and chemical treatment, simulating the biologic properties of the TSE agent. Microcolonies of spiroplasma embedded in biofilm bound to clay are the likely mechanism of lateral transmission of scrapie in sheep and chronic wasting disease in deer via soil ingestion. Spiroplasma in biofilm bound to the stainless steel of surgical instruments may also cause iatrogenic transmission of Creutzfeldt-Jakob disease. Sessile spiroplasma in biofilm attach to the surface by curli-like fibrils, a functional amyloid that is important for spiroplasma entering cells. Curli fibers have been shown to interact with host proteins and initiate formation of a potentially toxic amyloid that multiplies by self-assembly. In TSE, this mechanism may explain how spiroplasma trigger the formation of prion amyloid. This possibility is supported by experiments that show spiroplasma produce α-synuclein in mammalian tissue cultures. The data linking spiroplasma to neurodegenerative diseases provide a rationale for developing diagnostic tests for TSE based on the presence of spiroplasma-specific proteins or nucleic acid. Research efforts should focus on this bacterium for development of therapeutic regimens for Creutzfeldt-Jakob disease.

Streptococcus pneumoniae biofilm formation is strain dependent, multifactorial, and associated with reduced invasiveness and immunoreactivity during colonization

Biofilms are thought to play an important role during colonization of the nasopharynx by Streptococcus pneumoniae, yet how they form in vivo and the determinants responsible remain unknown. Using scanning electron microscopy, we show that biofilm aggregates of increasing complexity form on murine nasal septa following intranasal inoculation. These biofilms were highly distinct from in vitro biofilms, as they were discontiguous and appeared to incorporate nonbacterial components such as intact host cells. Biofilms initially formed on the surface of ciliated epithelial cells and, as cells were sloughed off, were found on the basement membrane. The size and number of biofilm aggregates within nasal lavage fluid were digitally quantitated and revealed strain-specific capabilities that loosely correlated with the ability to form robust in vitro biofilms. We tested the ability of isogenic mutants deficient in CbpA, pneumolysin, hydrogen peroxide, LytA, LuxS, CiaR/H, and PsrP to form biofilms within the nasopharynx. This analysis revealed that CiaR/H was absolutely required for colonization, that PsrP and SpxB strongly impacted aggregate formation, and that other determinants affected aggregate morphology in a modest fashion. We determined that mice colonized with ΔpsrP mutants had greater levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), IL-1β, and KC in nasal lavage fluid than did mice colonized with wild-type controls. This phenotype correlated with a diminished capacity of biofilm pneumococci to invade host cells in vitro despite enhanced attachment. Our results show that biofilms form during colonization and suggest that they may contribute to persistence through a hyperadhesive, noninvasive state that elicits a dampened cytokine response.

IMPORTANCE

This work demonstrates the first temporal characterization of Streptococcus pneumoniae biofilm formation in vivo. Our results show that the morphology of biofilms formed by both invasive and noninvasive clinical isolates in vivo is distinct from that of formed biofilms in vitro, yet propensity to form biofilms in vivo loosely correlates with the degree of in vitro biofilm formation on a microtiter plate. We show that host components, including intact host cells, influence the formation of in vivo structures. We also found that efficient biofilm formation in vivo requires multiple bacterial determinants. While some factors are essential for in vivo biofilm formation (CiaRH, PsrP, and SpxB), other factors are less critical (CbpA, LytA, LuxS, and pneumolysin). In comparison to their planktonic counterparts, biofilm pneumococci are hyperadhesive but less invasive and elicit a weaker proinflammatory cytokine response. These findings give insight into the requirements for and potential role of biofilms during prolonged asymptomatic colonization.

Current concepts in host-microbe interaction leading to pneumococcal pneumonia

PURPOSE OF REVIEW

Infection with Streptococcus pneumoniae (pneumococcus) results in colonization, which can lead to local or invasive disease, of which pneumonia is the most common manifestation. Despite the availability of pneumococcal vaccines, pneumococcal pneumonia is the leading cause of community and inhospital pneumonia in the United States and globally. This article discusses new insights into the pathogenesis of pneumococcal disease.

RECENT FINDINGS

The host-microbe interactions that determine whether pneumococcal colonization will result in clearance or invasive disease are highly complex. This article focuses on new information in three areas that bear on the pathogenesis of pneumococcal disease: factors that govern colonization, the prelude to invasive disease, including effects on colonization and invasion of capsular serotype, pneumolysin, surface proteins that regulate complement deposition, biofilm formation and agglutination; the effect of coinfection with other bacteria and viruses on pneumococcal growth and virulence, including the synergistic effect of influenza virus; and the contribution of the host inflammatory response to the pathogenesis of pneumococcal pneumonia, including the effects of pattern recognition molecules, cells that enhance and modulate inflammation, and therapies that modulate inflammation, such as statins.

SUMMARY

Recent research on pneumococcal pathogenesis reveals new mechanisms by which microbial factors govern the ability of pneumococcus to progress from the state of colonization to disease and host inflammatory responses contribute to the development of pneumonia. These mechanisms suggest that therapies which modulate the inflammatory response could hold promise for ameliorating damage stemming from the host inflammatory response in pneumococcal disease.

Interkingdom signaling induces Streptococcus pneumoniae biofilm dispersion and transition from asymptomatic colonization to disease

Streptococcus pneumoniae is a common human nasopharyngeal commensal colonizing 10% to 40% of healthy individuals, depending on age. Despite a low invasive disease rate, widespread carriage ensures that infection occurs often enough to make S. pneumoniae a leading bacterial cause of respiratory disease worldwide. However, the mechanisms behind transition from asymptomatic colonization to dissemination and disease in otherwise sterile sites remain poorly understood but are epidemiologically strongly linked to infection with respiratory viruses. In this report, we show that infection with influenza A virus and treatment with the resulting host signals (febrile-range temperatures, norepinephrine, extracytoplasmic ATP, and increased nutrient availability) induce the release of bacteria from biofilms in a newly developed biofilm model on live epithelial cells both in vitro and during in vivo colonization. These dispersed bacteria have distinct phenotypic properties different from those of both biofilm and broth-grown, planktonic bacteria, with the dispersed population showing differential virulence gene expression characteristics resulting in a significantly increased ability to disseminate and cause infection of otherwise sterile sites, such as the middle ear, lungs, and bloodstream. The results offer novel and important insights into the role of interkingdom signaling between microbe and host during biofilm dispersion and transition to acute disease.

This report addresses the mechanisms involved in transition from pneumococcal asymptomatic colonization to disease. In this study, we determined that changes in the nasopharyngeal environment result in the release of bacteria from colonizing biofilms with a gene expression and virulence phenotype different not only from that of colonizing biofilm bacteria but also from that of the broth-grown planktonic bacteria commonly used for pathogenesis studies. The work importantly also identifies specific host factors responsible for the release of bacteria and their changed phenotype. We show that these interkingdom signals are recognized by bacteria and are induced by influenza virus infection, which is epidemiologically strongly associated with transition to secondary pneumococcal disease. As virus infection is a common inducer of transition to disease among species occupying the nasopharynx, the results of this study may provide a basis for better understanding of the signals involved in the transition from colonization to disease in the human nasopharynx.

Biofilm formation avoids complement immunity and phagocytosis of Streptococcus pneumoniae

Streptococcus pneumoniae is a frequent member of the microbiota of the human nasopharynx. Colonization of the nasopharyngeal tract is a first and necessary step in the infectious process and often involves the formation of sessile microbial communities by this human pathogen. The ability to grow and persist as biofilms is an advantage for many microorganisms, because biofilm-grown bacteria show reduced susceptibility to antimicrobial agents and hinder recognition by the immune system. The extent of host protection against biofilm-related pneumococcal disease has not been determined yet. Using pneumococcal strains growing as planktonic cultures or as biofilms, we have investigated the recognition of S. pneumoniae by the complement system and its interactions with human neutrophils. Deposition of C3b, the key complement component, was impaired on S. pneumoniae biofilms. In addition, binding of C-reactive protein and the complement component C1q to the pneumococcal surface was reduced in biofilm bacteria, demonstrating that pneumococcal biofilms avoid the activation of the classical complement pathway. In addition, recruitment of factor H, the downregulator of the alternative pathway, was enhanced by S. pneumoniae growing as biofilms. Our results also show that biofilm formation diverts the alternative complement pathway activation by a PspC-mediated mechanism. Furthermore, phagocytosis of pneumococcal biofilms was also impaired. The present study confirms that biofilm formation in S. pneumoniae is an efficient means of evading both the classical and the PspC-dependent alternative complement pathways the host immune system.

A role for glycosylated serine-rich repeat proteins in gram-positive bacterial pathogenesis

Bacterial attachment to host surfaces is a pivotal event in the biological and infectious processes of both commensal and pathogenic bacteria, respectively. Serine-rich repeat proteins (SRRPs) are a family of adhesins in Gram-positive bacteria that mediate attachment to a variety of host and bacterial surfaces. As such, they contribute towards a wide-range of diseases including sub-acute bacterial endocarditis, community-acquired pneumonia, and meningitis. SRRPs are unique in that they are glycosylated, require a non-canonical Sec-translocase for transport, and are largely composed of a domain containing hundreds of alternating serine residues. These serine-rich repeats are thought to extend a unique non-repeat (NR) domain outward away from the bacterial surface to mediate adhesion. So far, NR domains have been determined to bind to sialic acid moieties, keratins, or other NR domains of a similar SRRP. This review summarizes how this important family of bacterial adhesins mediates bacterial attachment to host and bacterial cells, contributes to disease pathogenesis, and might be targeted for pharmacological intervention or used as novel protective vaccine antigens. This review also highlights recent structural findings on the NR domains of these proteins.

Future perspective on host-pathogen interactions during bacterial biofilm formation within the nasopharynx

Nasopharyngeal colonization provides bacteria with a place of residence, a platform for person-to-person transmission and for many opportunistic pathogens it is a prerequisite event towards the development of invasive disease. Therefore, how host factors within the nasopharynx contribute to, inhibit or otherwise shape biofilm formation, the primary mode of existence for colonizing bacteria, and how biofilm bacteria subvert the acute inflammatory response that facilitates clearance, are important topics for future microbiological research. This review proposes the examination of host components as bridging molecules for bacterial interactions during biofilm formation, altered virulence determinant production and cell wall modification as a mechanism for immunoquiescence, and the role of host factors as signals and co-opted mechanisms for bacterial dissemination, together providing an opportunity for disease.