Toxin-Antitoxin Genes of the Gram-Positive Pathogen Streptococcus pneumoniae: So Few and Yet So Many

SUMMARYPneumococcal infections cause up to 2 million deaths annually and raise a large economic burden and thus constitute an important threat to mankind. Because of the increase in the antibiotic resistance ofStreptococcus pneumoniaeclinical isolates, there is an urgent need to find new antimicrobial approaches to triumph over pneumococcal infections. Toxin-antitoxin (TA) systems (TAS), which are present in most living bacteria but not in eukaryotes, have been proposed as an effective strategy to combat bacterial infections. Type II TAS comprise a stable toxin and a labile antitoxin that form an innocuous TA complex under normal conditions. Under stress conditions, TA synthesis will be triggered, resulting in the degradation of the labile antitoxin and the release of the toxin protein, which would poison the host cells. The three functional chromosomal TAS fromS. pneumoniaethat have been studied as well as their molecular characteristics are discussed in detail in this review. Furthermore, a meticulous bioinformatics search has been performed for 48 pneumococcal genomes that are found in public databases, and more putative TAS, homologous to well-characterized ones, have been revealed. Strikingly, several unusual putative TAS, in terms of components and genetic organizations previously not envisaged, have been discovered and are further discussed. Previously, we reported a novel finding in which a unique pneumococcal DNA signature, the BOX element, affected the regulation of the pneumococcalyefM-yoeBTAS. This BOX element has also been found in some of the other pneumococcal TAS. In this review, we also discuss possible relationships between some of the pneumococcal TAS with pathogenicity, competence, biofilm formation, persistence, and an interesting phenomenon called bistability.

Download Full-text

Streptococcus pneumoniae Biofilm Formation Is Strain Dependent, Multifactorial, and Associated with Reduced Invasiveness and Immunoreactivity during Colonization

mBio ◽

10.1128/mbio.00745-13 ◽

2013 ◽

Vol 4 (5) ◽

Cited By ~ 68

Author(s):

Krystle Blanchette-Cain ◽

Cecilia A. Hinojosa ◽

Ramya Akula Suresh Babu ◽

Anel Lizcano ◽

Norberto Gonzalez-Juarbe ◽

...

Keyword(s):

Streptococcus Pneumoniae ◽

Biofilm Formation ◽

Lavage Fluid ◽

Cytokine Response ◽

Host Cells ◽

Nasal Lavage ◽

Content Type ◽

Nasal Lavage Fluid

ABSTRACT 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.

Download Full-text

Immunomodulatory Effects of Pneumococcal Extracellular Vesicles on Cellular and Humoral Host Defenses

mBio ◽

10.1128/mbio.00559-18 ◽

2018 ◽

Vol 9 (2) ◽

Cited By ~ 17

Author(s):

Mario Codemo ◽

Sandra Muschiol ◽

Federico Iovino ◽

Priyanka Nannapaneni ◽

Laura Plant ◽

...

Keyword(s):

Dendritic Cells ◽

Plasma Membrane ◽

Streptococcus Pneumoniae ◽

Extracellular Vesicles ◽

Factor H ◽

Host Cells ◽

Immunomodulatory Effects ◽

Content Type ◽

Associated Proteins ◽

Tract Infections

ABSTRACTGram-positive bacteria, including the major respiratory pathogenStreptococcus pneumoniae, were recently shown to produce extracellular vesicles (EVs) that likely originate from the plasma membrane and are released into the extracellular environment. EVs may function as cargo for many bacterial proteins, however, their involvement in cellular processes and their interactions with the innate immune system are poorly understood. Here, EVs from pneumococci were characterized and their immunomodulatory effects investigated. Pneumococcal EVs were protruding from the bacterial surface and released into the medium as 25 to 250 nm lipid stained vesicles containing a large number of cytosolic, membrane, and surface-associated proteins. The cytosolic pore-forming toxin pneumolysin was significantly enriched in EVs compared to a total bacterial lysate but was not required for EV formation. Pneumococcal EVs were internalized into A549 lung epithelial cells and human monocyte-derived dendritic cells and induced proinflammatory cytokine responses irrespective of pneumolysin content. EVs from encapsulated pneumococci were recognized by serum proteins, resulting in C3b deposition and formation of C5b-9 membrane attack complexes as well as factor H recruitment, depending on the presence of the choline binding protein PspC. Addition of EVs to human serum decreased opsonophagocytic killing of encapsulated pneumococci. Our data suggest that EVs may act in an immunomodulatory manner by allowing delivery of vesicle-associated proteins and other macromolecules into host cells. In addition, EVs expose targets for complement factors in serum, promoting pneumococcal evasion of humoral host defense.IMPORTANCEStreptococcus pneumoniaeis a major contributor to morbidity and mortality worldwide, being the major cause of milder respiratory tract infections such as otitis and sinusitis and of severe infections such as community-acquired pneumonia, with or without septicemia, and meningitis. More knowledge is needed on how pneumococci interact with the host, deliver virulence factors, and activate immune defenses. Here we show that pneumococci form extracellular vesicles that emanate from the plasma membrane and contain virulence properties, including enrichment of pneumolysin. We found that pneumococcal vesicles can be internalized into epithelial and dendritic cells and bind complement proteins, thereby promoting pneumococcal evasion of complement-mediated opsonophagocytosis. They also induce pneumolysin-independent proinflammatory responses. We suggest that these vesicles can function as a mechanism for delivery of pneumococcal proteins and other immunomodulatory components into host cells and help pneumococci to avoid complement deposition and phagocytosis-mediated killing, thereby possibly contributing to the symptoms found in pneumococcal infections.

Download Full-text

Reassessing the Role of Type II Toxin-Antitoxin Systems in Formation ofEscherichia coliType II Persister Cells

mBio ◽

10.1128/mbio.00640-18 ◽

2018 ◽

Vol 9 (3) ◽

Cited By ~ 71

Author(s):

Frédéric Goormaghtigh ◽

Nathan Fraikin ◽

Marta Putrinš ◽

Thibaut Hallaert ◽

Vasili Hauryliuk ◽

...

Keyword(s):

Antibiotic Treatment ◽

Bacterial Infections ◽

Bacterial Population ◽

Transient State ◽

Health Concern ◽

Type Ii ◽

Direct Link ◽

Persister Cells ◽

Content Type ◽

High Fluorescence

ABSTRACTPersistence is a reversible and low-frequency phenomenon allowing a subpopulation of a clonal bacterial population to survive antibiotic treatments. Upon removal of the antibiotic, persister cells resume growth and give rise to viable progeny. Type II toxin-antitoxin (TA) systems were assumed to play a key role in the formation of persister cells inEscherichia colibased on the observation that successive deletions of TA systems decreased persistence frequency. In addition, the model proposed that stochastic fluctuations of (p)ppGpp levels are the basis for triggering activation of TA systems. Cells in which TA systems are activated are thought to enter a dormancy state and therefore survive the antibiotic treatment. Using independently constructed strains and newly designed fluorescent reporters, we reassessed the roles of TA modules in persistence both at the population and single-cell levels. Our data confirm that the deletion of 10 TA systems does not affect persistence to ofloxacin or ampicillin. Moreover, microfluidic experiments performed with a strain reporting the induction of theyefM-yoeBTA system allowed the observation of a small number of type II persister cells that resume growth after removal of ampicillin. However, we were unable to establish a correlation between high fluorescence and persistence, since the fluorescence of persister cells was comparable to that of the bulk of the population and none of the cells showing high fluorescence were able to resume growth upon removal of the antibiotic. Altogether, these data show that there is no direct link between induction of TA systems and persistence to antibiotics.IMPORTANCEWithin a growing bacterial population, a small subpopulation of cells is able to survive antibiotic treatment by entering a transient state of dormancy referred to as persistence. Persistence is thought to be the cause of relapsing bacterial infections and is a major public health concern. Type II toxin-antitoxin systems are small modules composed of a toxic protein and an antitoxin protein counteracting the toxin activity. These systems were thought to be pivotal players in persistence until recent developments in the field. Our results demonstrate that previous influential reports had technical flaws and that there is no direct link between induction of TA systems and persistence to antibiotics.

Download Full-text

The N-Acetylglucosaminidase LytB of Streptococcus pneumoniae Is Involved in the Structure and Formation of Biofilms

Applied and Environmental Microbiology ◽

10.1128/aem.00280-20 ◽

2020 ◽

Vol 86 (10) ◽

Cited By ~ 1

Author(s):

Mirian Domenech ◽

Ernesto García

Keyword(s):

Streptococcus Pneumoniae ◽

Biofilm Formation ◽

Single Gene ◽

Extracellular Polysaccharide ◽

Extracellular Dna ◽

Nasopharyngeal Colonization ◽

Content Type ◽

Daughter Cells ◽

Biofilm Matrix

ABSTRACT The N-acetylglucosaminidase LytB of Streptococcus pneumoniae is involved in nasopharyngeal colonization and is responsible for cell separation at the end of cell division; thus, ΔlytB mutants form long chains of cells. This paper reports the construction and properties of a defective pneumococcal mutant producing an inactive LytB protein (LytBE585A). It is shown that an enzymatically active LytB is required for in vitro biofilm formation, as lytB mutants (either ΔlytB or producing the inactive LytBE585A) are incapable of forming substantial biofilms, despite that extracellular DNA is present in the biofilm matrix. Adding small amounts (0.5 to 2.0 μg/ml) of exogenous LytB or some LytB constructs restored the biofilm-forming capacity of lytB mutants to wild-type levels. The LytBE585A mutant formed biofilm more rapidly than ΔlytB mutants in the presence of LytB. This suggests that the mutant protein acted in a structural role, likely through the formation of complexes with extracellular DNA. The chain-dispersing capacity of LytB allowed the separation of daughter cells, presumably facilitating the formation of microcolonies and, finally, of biofilms. A role for the possible involvement of LytB in the synthesis of the extracellular polysaccharide component of the biofilm matrix is also discussed. IMPORTANCE It has been previously accepted that biofilm formation in S. pneumoniae must be a multigenic trait because the mutation of a single gene has led to only to partial inhibition of biofilm production. In the present study, however, evidence that the N-acetylglucosaminidase LytB is crucial in biofilm formation is provided. Despite the presence of extracellular DNA, strains either deficient in LytB or producing a defective LytB enzyme formed only shallow biofilms.

Download Full-text

The LuxS-Dependent Quorum-Sensing System Regulates Early Biofilm Formation by Streptococcus pneumoniae Strain D39

Infection and Immunity ◽

10.1128/iai.05186-11 ◽

2011 ◽

Vol 79 (10) ◽

pp. 4050-4060 ◽

Cited By ~ 82

Author(s):

Jorge E. Vidal ◽

Herbert P. Ludewick ◽

Rebekah M. Kunkel ◽

Dorothea Zähner ◽

Keith P. Klugman

Keyword(s):

Streptococcus Pneumoniae ◽

Quorum Sensing ◽

Biofilm Formation ◽

Single Copy ◽

Middle Ear Mucosa ◽

Transcript Levels ◽

Content Type ◽

Sensing System ◽

Quorum Sensing System

ABSTRACTStreptococcus pneumoniaeis the leading cause of death in children worldwide and forms highly organized biofilms in the nasopharynx, lungs, and middle ear mucosa. TheluxS-controlled quorum-sensing (QS) system has recently been implicated in virulence and persistence in the nasopharynx, but its role in biofilms has not been studied. Here we show that this QS system plays a major role in the control ofS. pneumoniaebiofilm formation. Our results demonstrate that theluxSgene is contained by invasive isolates and normal-flora strains in a region that contains genes involved in division and cell wall biosynthesis. TheluxSgene was maximally transcribed, as a monocistronic message, in the early mid-log phase of growth, and this coincides with the appearance of early biofilms. Demonstrating the role of the LuxS system in regulatingS. pneumoniaebiofilms, at 24 h postinoculation, two different D39ΔluxSmutants produced ∼80% less biofilm biomass than wild-type (WT) strain D39 did. Complementation of these strains withluxS, either in a plasmid or integrated as a single copy in the genome, restored their biofilm level to that of the WT. Moreover, a soluble factor secreted by WT strain D39 or purified AI-2 restored the biofilm phenotype of D39ΔluxS. Our results also demonstrate that during the early mid-log phase of growth, LuxS regulates the transcript levels oflytA, which encodes an autolysin previously implicated in biofilms, and also the transcript levels ofply, which encodes the pneumococcal pneumolysin. In conclusion, theluxS-controlled QS system is a key regulator of early biofilm formation byS. pneumoniaestrain D39.

Download Full-text

Accumulation-Associated Protein Enhances Staphylococcus epidermidis Biofilm Formation under Dynamic Conditions and Is Required for Infection in a Rat Catheter Model

Infection and Immunity ◽

10.1128/iai.02177-14 ◽

2014 ◽

Vol 83 (1) ◽

pp. 214-226 ◽

Cited By ~ 63

Author(s):

Carolyn R. Schaeffer ◽

Keith M. Woods ◽

G. Matt Longo ◽

Megan R. Kiedrowski ◽

Alexandra E. Paharik ◽

...

Keyword(s):

Staphylococcus Epidermidis ◽

Biofilm Formation ◽

Host Cells ◽

Content Type ◽

Microtiter Plates ◽

Allelic Replacement ◽

Abiotic Surfaces ◽

Cell Accumulation ◽

Accumulation Associated Protein

Biofilm formation is the primary virulence factor ofStaphylococcus epidermidis.S. epidermidisbiofilms preferentially form on abiotic surfaces and may contain multiple matrix components, including proteins such as accumulation-associated protein (Aap). Following proteolytic cleavage of the A domain, which has been shown to enhance binding to host cells, B domain homotypic interactions support cell accumulation and biofilm formation. To further define the contribution of Aap to biofilm formation and infection, we constructed anaapallelic replacement mutant and anicaADBC aapdouble mutant. When subjected to fluid shear, strains deficient in Aap production produced significantly less biofilm than Aap-positive strains. To examine thein vivorelevance of our findings, we modified our previously described rat jugular catheter model and validated the importance of immunosuppression and the presence of a foreign body to the establishment of infection. The use of our allelic replacement mutants in the model revealed a significant decrease in bacterial recovery from the catheter and the blood in the absence of Aap, regardless of the production of polysaccharide intercellular adhesin (PIA), a well-characterized, robust matrix molecule. Complementation of theaapmutant with full-length Aap (containing the A domain), but not the B domain alone, increased initial attachment to microtiter plates, as did intransexpression of the A domain in adhesion-deficientStaphylococcus carnosus. These results demonstrate Aap contributes toS. epidermidisinfection, which may in part be due to A domain-mediated attachment to abiotic surfaces.

Download Full-text

Thermoregulation of Pseudomonas aeruginosa Biofilm Formation

Applied and Environmental Microbiology ◽

10.1128/aem.01584-20 ◽

2020 ◽

Vol 86 (22) ◽

Author(s):

Suran Kim ◽

Xi-Hui Li ◽

Hyeon-Ji Hwang ◽

Joon-Hee Lee

Keyword(s):

Pseudomonas Aeruginosa ◽

Biofilm Formation ◽

Bacterial Infections ◽

Effect Of Temperature ◽

Cyclic Diguanylate ◽

Content Type ◽

Protection Mechanism ◽

Formation Pattern ◽

Temperature Ranges ◽

Different Strains

ABSTRACT We investigated the effect of temperature on the biofilm formation of Pseudomonas aeruginosa and revealed that the biofilm formation increased rapidly at temperatures lower than 25°C. P. aeruginosa formed the most robust biofilm of a conspicuous mushroom-like structure at 20°C. However, when the temperature increased to 25°C, the biofilm formation rapidly decreased. Above 25°C, as the temperature rose, the biofilm formation increased again little by little despite its less-structured form, indicating that 25°C is the low point of biofilm formation. The intracellular 3′,5′-cyclic diguanylate (c-di-GMP) levels also decreased rapidly as the temperature rose from 20 to 25°C. The expression levels of pelA, algD, and pslA encoding Pel, alginate, and Psl, respectively, were also dramatically affected by temperature, with pelA being regulated in a pattern similar to that of the intracellular c-di-GMP levels, and the pattern seen for algD regulation was the most similar to the actual biofilm formation pattern. Total exopolysaccharide production was thermoregulated and followed the regulation pattern of c-di-GMP. Interestingly, the thermoregulation patterns in biofilm formation were different depending on the strain of P. aeruginosa. Unlike PAO1, another strain, PA14, showed a gradual decrease in biofilm formation and c-di-GMP in the range of 20 to 37°C, and P. aeruginosa clinical isolates also showed slightly different patterns in biofilm formation in conjunction with temperature change, suggesting that different strains may sense different temperature ranges for biofilm formation. However, it is obvious that P. aeruginosa forms more biofilms at lower temperatures and that temperature is an important factor in determining the biofilm formation. IMPORTANCE Biofilm formation is an important protection mechanism used by most microorganisms and provides cells with many advantages, like high infectivity, antibiotic resistance, and strong survivability. Since most persistent bacterial infections are believed to be associated with biofilms, biofilm control is an important issue in medicine, environmental engineering, and industry. Biofilm formation is influenced by various environmental factors. Temperature is the most direct environmental cue encountered by microorganisms. Here, we investigated the effect of temperature on the biofilm formation of P. aeruginosa, a notorious pathogen, and found that temperature is an important factor determining the amount and structure of biofilms. Low temperatures greatly increase biofilm formation and give biofilms a highly conspicuous structure. Although thermoregulation of biofilm formation is mainly mediated by c-di-GMP, some c-di-GMP-independent regulations were also observed. This study shows how biofilms are formed at various temperatures and provides new insights to control biofilms using temperature.

Download Full-text

Genotoxic Effect of Salmonella Paratyphi A Infection on Human Primary Gallbladder Cells

mBio ◽

10.1128/mbio.01911-20 ◽

2020 ◽

Vol 11 (5) ◽

Author(s):

Ludovico P. Sepe ◽

Kimberly Hartl ◽

Amina Iftekhar ◽

Hilmar Berger ◽

Naveen Kumar ◽

...

Keyword(s):

Dna Damage ◽

Genomic Instability ◽

Salmonella Enterica ◽

Bacterial Infections ◽

Molecular Mechanisms ◽

Host Cells ◽

Dna Breaks ◽

Human Gallbladder ◽

Content Type ◽

Typhoid Toxin

ABSTRACT Carcinoma of the gallbladder (GBC) is the most frequent tumor of the biliary tract. Despite epidemiological studies showing a correlation between chronic infection with Salmonella enterica Typhi/Paratyphi A and GBC, the underlying molecular mechanisms of this fatal connection are still uncertain. The murine serovar Salmonella Typhimurium has been shown to promote transformation of genetically predisposed cells by driving mitogenic signaling. However, insights from this strain remain limited as it lacks the typhoid toxin produced by the human serovars Typhi and Paratyphi A. In particular, the CdtB subunit of the typhoid toxin directly induces DNA breaks in host cells, likely promoting transformation. To assess the underlying principles of transformation, we used gallbladder organoids as an infection model for Salmonella Paratyphi A. In this model, bacteria can invade epithelial cells, and we observed host cell DNA damage. The induction of DNA double-strand breaks after infection depended on the typhoid toxin CdtB subunit and extended to neighboring, non-infected cells. By cultivating the organoid derived cells into polarized monolayers in air-liquid interphase, we could extend the duration of the infection, and we observed an initial arrest of the cell cycle that does not depend on the typhoid toxin. Non-infected intoxicated cells instead continued to proliferate despite the DNA damage. Our study highlights the importance of the typhoid toxin in causing genomic instability and corroborates the epidemiological link between Salmonella infection and GBC. IMPORTANCE Bacterial infections are increasingly being recognized as risk factors for the development of adenocarcinomas. The strong epidemiological evidence linking Helicobacter pylori infection to stomach cancer has paved the way to the demonstration that bacterial infections cause DNA damage in the host cells, initiating transformation. In this regard, the role of bacterial genotoxins has become more relevant. Salmonella enterica serovars Typhi and Paratyphi A have been clinically associated with gallbladder cancer. By harnessing the stem cell potential of cells from healthy human gallbladder explant, we regenerated and propagated the epithelium of this organ in vitro and used these cultures to model S. Paratyphi A infection. This study demonstrates the importance of the typhoid toxin, encoded only by these specific serovars, in causing genomic instability in healthy gallbladder cells, posing intoxicated cells at risk of malignant transformation.

Download Full-text

Inhibition of Protein Secretion inEscherichia coliand Sub-MIC Effects of Arylomycin Antibiotics

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01253-18 ◽

2018 ◽

Vol 63 (2) ◽

pp. e01253-18 ◽

Cited By ~ 4

Author(s):

Shawn I. Walsh ◽

David S. Peters ◽

Peter A. Smith ◽

Arryn Craney ◽

Melissa M. Dix ◽

...

Keyword(s):

Mass Spectrometry ◽

Biofilm Formation ◽

Bacterial Infections ◽

Protein Identification ◽

Secretory Pathway ◽

Signal Peptidase ◽

Type I ◽

Content Type ◽

Multidimensional Protein Identification Technology ◽

Bacterial Type

ABSTRACTAt sufficient concentrations, antibiotics effectively eradicate many bacterial infections. However, during therapy, bacteria are unavoidably exposed to lower antibiotic concentrations, and sub-MIC exposure can result in a wide variety of other effects, including the induction of virulence, which can complicate therapy, or horizontal gene transfer (HGT), which can accelerate the spread of resistance genes. Bacterial type I signal peptidase (SPase) is an essential protein that acts at the final step of the general secretory pathway. This pathway is required for the secretion of many proteins, including many required for virulence, and the arylomycins are a class of natural product antibiotics that target SPase. Here, we investigated the consequences of exposingEscherichia colicultures to sub-MIC levels of an arylomycin. Using multidimensional protein identification technology mass spectrometry, we found that arylomycin treatment inhibits the proper extracytoplasmic localization of many proteins, both those that appear to be SPase substrates and several that do not. The identified proteins are involved in a broad range of extracytoplasmic processes and include a number of virulence factors. The effects of arylomycin on several processes required for virulence were then individually examined, and we found that, at even sub-MIC levels, the arylomycins potently inhibit flagellation, motility, biofilm formation, and the dissemination of antibiotic resistance via HGT. Thus, we conclude that the arylomycins represent promising novel therapeutics with the potential to eradicate infections while simultaneously reducing virulence and the dissemination of resistance.

Download Full-text

Biofilm Formation Avoids Complement Immunity and Phagocytosis of Streptococcus pneumoniae

Infection and Immunity ◽

10.1128/iai.00491-13 ◽

2013 ◽

Vol 81 (7) ◽

pp. 2606-2615 ◽

Cited By ~ 81

Author(s):

Mirian Domenech ◽

Elisa Ramos-Sevillano ◽

Ernesto García ◽

Miriam Moscoso ◽

Jose Yuste

Keyword(s):

Immune System ◽

Streptococcus Pneumoniae ◽

Biofilm Formation ◽

Complement Component ◽

Factor H ◽

Human Neutrophils ◽

Host Immune System ◽

Complement Pathway ◽

Content Type ◽

Alternative Complement

ABSTRACTStreptococcus pneumoniaeis 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 ofS. pneumoniaeby the complement system and its interactions with human neutrophils. Deposition of C3b, the key complement component, was impaired onS. pneumoniaebiofilms. 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 byS. pneumoniaegrowing 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 inS. pneumoniaeis an efficient means of evading both the classical and the PspC-dependent alternative complement pathways the host immune system.

Download Full-text