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Journal of Neuroinflammation May 2019Streptococcus pneumoniae is the cause of a highly lethal form of meningitis in humans. Microglial cells in the brain represent the first line of defense against...
BACKGROUND
Streptococcus pneumoniae is the cause of a highly lethal form of meningitis in humans. Microglial cells in the brain represent the first line of defense against pathogens, and they participate in the inflammatory response. The cholesterol-dependent cytolysin pneumolysin and the bacterial capsule are key pathogenic factors, known to exacerbate the course of pneumococcal meningitis.
METHODS
We utilized live imaging and immunostaining of glial cells in dissociated and acute brain slice cultures to study the effect of pneumococcal factors, including the cholesterol-dependent cytolysin pneumolysin and the pneumococcal capsule, on microglial motility and taxis.
RESULTS
In brain tissue, primary microglia cells showed an enhanced response towards lysates from bacteria lacking capsules and pneumolysin as they moved rapidly to areas with an abundance of bacterial factors. The presence of bacterial capsules and pneumolysin cumulatively inhibited microglial taxis. In mixed cultures of astrocytes and microglia, the motility of microglia was inhibited by capsular components within minutes after exposure. The reduced motility was partially reversed by mannan, a mannose receptor inhibitor. The effects on microglia were not mediated by astrocytes because pure microglial cells responded to various pneumococcal lysates similarly with distinct cell shape changes as seen in mixed cultures.
CONCLUSIONS
Our data indicate that microglia possess the capacity for a very agile response towards bacterial pathogens, but key pathogenic factors, such as pneumococcal capsules and pneumolysin, inhibited this response shortly after a bacterial challenge. Furthermore, we demonstrate for the first time that the bacterial capsule affects cellular behaviors such as motility and taxis.
Topics: Animals; Bacterial Capsules; Bacterial Proteins; Cell Movement; Cells, Cultured; Chemotaxis; Coculture Techniques; Mice; Mice, Inbred C57BL; Microglia; Organ Culture Techniques; Streptococcus pneumoniae; Streptolysins
PubMed: 31103037
DOI: 10.1186/s12974-019-1491-7 -
MBio Aug 2017The capsular polysaccharide (CPS) of is characterized by its diversity, as it has over 95 known serotypes, and the variation in its thickness as it surrounds an...
The capsular polysaccharide (CPS) of is characterized by its diversity, as it has over 95 known serotypes, and the variation in its thickness as it surrounds an organism. While within-host effects of CPS have been studied in detail, there is no information about its contribution to host-to-host transmission. In this study, we used an infant mouse model of intralitter transmission, together with isogenic capsule switch and promoter switch constructs, to explore the effects of CPS type and amount. The determining factor in the transmission rate in this model is the number of pneumococci shed in nasal secretions by colonized hosts. Two of seven capsule switch constructs showed reduced shedding. These constructs were unimpaired in colonization and expressed capsules similar in size to those of the wild-type strain. A promoter switch mutant expressing ~50% of wild-type amounts of CPS also displayed reduced shedding without a defect in colonization. Since shedding from the mucosal surface may require escape from mucus entrapment, a mucin-binding assay was used to compare capsule switch and promoter switch mutants. The CPS type or amount constructs that shed poorly were bound more robustly by immobilized mucin. These capsule switch and promoter switch constructs with increased mucin-binding affinity and reduced shedding also had lower rates of pup-to-pup transmission. Our results demonstrate that CPS type and amount affect transmission dynamics and may contribute to the marked differences in prevalence among pneumococcal types., a leading cause of morbidity and mortality, is readily transmitted, especially among young children. Its structurally and antigenically diverse capsular polysaccharide is the target of currently licensed pneumococcal vaccines. Epidemiology studies show that only a subset of the >95 distinct serotypes are prevalent in the human population, suggesting that certain capsular polysaccharide types might be more likely to be transmitted within the community. Herein, we used an infant mouse model to show that both capsule type and amount are important determinants in the spread of pneumococci from host to host. Transmission rates correlate with those capsule types that are better at escaping mucus entrapment, a key step in exiting the host upper respiratory tract. Hence, our study provides a better mechanistic understanding of why certain pneumococcal serotypes are more common in the human population.
Topics: Animals; Animals, Newborn; Bacterial Capsules; Bacterial Shedding; Disease Models, Animal; Host-Pathogen Interactions; Mice; Mucus; Mutation; Nose; Pneumococcal Infections; Polysaccharides, Bacterial; Respiratory Tract Infections; Streptococcus pneumoniae
PubMed: 28830943
DOI: 10.1128/mBio.00989-17 -
MBio Mar 2016While significant protection from pneumococcal disease has been achieved by the use of polysaccharide and polysaccharide-protein conjugate vaccines, capsule-independent... (Review)
Review
While significant protection from pneumococcal disease has been achieved by the use of polysaccharide and polysaccharide-protein conjugate vaccines, capsule-independent protection has been limited by serotype replacement along with disease caused by nonencapsulatedStreptococcus pneumoniae(NESp). NESp strains compose approximately 3% to 19% of asymptomatic carriage isolates and harbor multiple antibiotic resistance genes. Surface proteins unique to NESp enhance colonization and virulence despite the lack of a capsule even though the capsule has been thought to be required for pneumococcal pathogenesis. Genes for pneumococcal surface proteins replace the capsular polysaccharide (cps) locus in some NESp isolates, and these proteins aid in pneumococcal colonization and otitis media (OM). NESp strains have been isolated from patients with invasive and noninvasive pneumococcal disease, but noninvasive diseases, specifically, conjunctivitis (85%) and OM (8%), are of higher prevalence. Conjunctival strains are commonly of the so-called classical NESp lineages defined by multilocus sequence types (STs) ST344 and ST448, while sporadic NESp lineages such as ST1106 are more commonly isolated from patients with other diseases. Interestingly, sporadic lineages have significantly higher rates of recombination than classical lineages. Higher rates of recombination can lead to increased acquisition of antibiotic resistance and virulence factors, increasing the risk of disease and hindering treatment. NESp strains are a significant proportion of the pneumococcal population, can cause disease, and may be increasing in prevalence in the population due to effects on the pneumococcal niche caused by pneumococcal vaccines. Current vaccines are ineffective against NESp, and further research is necessary to develop vaccines effective against both encapsulated and nonencapsulated pneumococci.
Topics: Bacterial Capsules; Carrier State; Humans; Pneumococcal Infections; Prevalence; Streptococcus pneumoniae; Virulence Factors
PubMed: 27006456
DOI: 10.1128/mBio.01792-15 -
Discovery and Characterization of Pneumococcal Serogroup 36 Capsule Subtypes, Serotypes 36A and 36B.Journal of Clinical Microbiology Apr 2023Streptococcus pneumoniae can produce a wide breadth of antigenically diverse capsule types, a fact that poses a looming threat to the success of vaccines that target...
Streptococcus pneumoniae can produce a wide breadth of antigenically diverse capsule types, a fact that poses a looming threat to the success of vaccines that target pneumococcal polysaccharide (PS) capsule. Yet, many pneumococcal capsule types remain undiscovered and/or uncharacterized. Prior sequence analysis of pneumococcal capsule synthesis () loci suggested the existence of capsule subtypes among isolates identified as "serotype 36" according to conventional capsule typing methods. We discovered these subtypes represent two antigenically similar but distinguishable pneumococcal capsule serotypes, 36A and 36B. Biochemical analysis of their capsule PS structure reveals that both have the shared repeat unit backbone [→5)-α-d-Gal-(1→1)-d-Rib-ol-(5→P→6)-β-d-ManNAc-(1→4)-β-d-Glc-(1→] with two branching structures. Both serotypes have a β-d-Gal branch to Ribitol. Serotypes 36A and 36B differ by the presence of a α-d-Glc-(1→3)-β-d-ManNAc or α-d-Gal-(1→3)-β-d-ManNAc branch, respectively. Comparison of the phylogenetically distant serogroup 9 and 36 loci, which all encode this distinguishing glycosidic bond, revealed that the incorporation of Glc (in types 9N and 36A) versus Gal (in types 9A, 9V, 9L, and 36B) is associated with the identity of four amino acids in the encoded glycosyltransferase WcjA. Identifying functional determinants of -encoded enzymes and their impact on capsule PS structure is key to improving the resolution and reliability of sequencing-based capsule typing methods and discovering novel capsule variants indistinguishable by conventional serotyping methods.
Topics: Humans; Streptococcus pneumoniae; Serogroup; Reproducibility of Results; Serotyping; Polysaccharides; Pneumococcal Vaccines; Bacterial Capsules; Pneumococcal Infections
PubMed: 36971549
DOI: 10.1128/jcm.00024-23 -
PLoS Biology Jul 2021The horizontal transfer of mobile DNA is one of the signature moves of bacterial evolution, but the specific rules that govern this transfer remain elusive. In this PLOS...
The horizontal transfer of mobile DNA is one of the signature moves of bacterial evolution, but the specific rules that govern this transfer remain elusive. In this PLOS Biology issue, Haudiquet and colleagues revealed that the interactions between mobile genetic elements and the bacterial capsule shape the horizontal flow of DNA in an important bacterial pathogen.
Topics: Bacteria; Bacterial Capsules; Gene Transfer, Horizontal
PubMed: 34228713
DOI: 10.1371/journal.pbio.3001308 -
Proceedings. Biological Sciences Mar 2021The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against...
The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against biotic aggressions or abiotic stress. However, it is unknown if the capsule contributes to fitness in the absence of these. Here, we explored conditions favouring the maintenance of the capsule in where the capsule is known to be a major virulence factor. Using short-term experimental evolution on different strains, we showed that small environmental variations have a strong impact on the maintenance of the capsule. Capsule inactivation is frequent in nutrient-rich, but scarce in nutrient-poor media. Competitions between wild-type and capsule mutants in nine different strains confirmed that the capsule is costly in nutrient-rich media. Surprisingly, these results also showed that the presence of a capsule provides a clear fitness advantage in nutrient-poor conditions by increasing both growth rates and population yields. The comparative analyses of the wild-type and capsule mutants reveal complex interactions between the environment, genetic background and serotype even in relation to traits known to be relevant during pathogenesis. In conclusion, our data suggest there are novel roles for bacterial capsules yet to be discovered and further supports the notion that the capsule's role in virulence may be a by-product of its contribution to bacterial adaptation outside the host.
Topics: Bacterial Capsules; Klebsiella; Klebsiella pneumoniae; Nutrients; Virulence
PubMed: 33653142
DOI: 10.1098/rspb.2020.2876 -
Virulence Oct 2016
Topics: Bacterial Capsules; Humans; Klebsiella; Klebsiella pneumoniae; Polysaccharides, Bacterial
PubMed: 27332888
DOI: 10.1080/21505594.2016.1204509 -
Microbes and Infection 2020The Gram-negative bacterium Klebsiella pneumoniae is an opportunistic pathogen, which can cause life-threatening infections such as sepsis. Worldwide, emerging multidrug...
The Gram-negative bacterium Klebsiella pneumoniae is an opportunistic pathogen, which can cause life-threatening infections such as sepsis. Worldwide, emerging multidrug resistant K. pneumoniae infections are challenging to treat, hence leading to increased mortality. Therefore, understanding the interactions between K. pneumoniae and the immune system is important to develop new treatment options. We characterized ten clinical K. pneumoniae isolates obtained from blood of bacteremia patients. The interaction of the isolates with human serum was investigated to elucidate how K. pneumoniae escapes the host immune system, and how complement activation by K. pneumoniae changed the capsule structure. All K. pneumoniae isolates activated the alternative complement pathway despite serum resistance of seven isolates. One serum sensitive isolate activated two or all three pathways, and this isolate was lysed and had numerous membrane attack complexes in the outer membrane. However, we also found deposition of complement components in the capsule of serum resistant isolates resulting in morphological capsule changes and capsule shedding. These bacteria did not lyse, and no membrane attack complex was observed despite deposition of C5b-9 within the capsule, indicating that the capsule of serum resistant K. pneumoniae isolates is a defense mechanism against complement-mediated lysis.
Topics: Bacteremia; Bacterial Capsules; Blood Bactericidal Activity; Complement Activation; Complement Membrane Attack Complex; Complement System Proteins; Host-Pathogen Interactions; Humans; Klebsiella Infections; Klebsiella pneumoniae
PubMed: 31473336
DOI: 10.1016/j.micinf.2019.08.003 -
Infection and Immunity Apr 2021Group B (GBS) is an opportunistic bacterial pathogen that can contribute to the induction of preterm birth in colonized pregnant women and to severe neonatal disease....
Group B (GBS) is an opportunistic bacterial pathogen that can contribute to the induction of preterm birth in colonized pregnant women and to severe neonatal disease. Many questions regarding the mechanisms that drive GBS-associated pathogenesis remain unanswered, and it is not yet clear why virulence has been observed to vary so extensively across GBS strains. Previously, we demonstrated that GBS strains of different sequence types (STs) and capsule (CPS) types induce different cytokine profiles in infected THP-1 macrophage-like cells. Here, we expanded on these studies by utilizing the same set of genetically diverse GBS isolates to assess ST and CPS-specific differences in upstream cell death and inflammatory signaling pathways. Our results demonstrate that particularly virulent STs and CPS types, such as the ST-17 and CPS III groups, induce enhanced Jun-N-terminal protein kinase (JNK) and NF-κB pathway activation following GBS infection of macrophages compared with other ST or CPS groups. Additionally, we found that ST-17, CPS III, and CPS V GBS strains induce the greatest levels of macrophage cell death during infection and exhibit a more pronounced ability to be internalized and to survive in macrophages following phagocytosis. These data provide further support for the hypothesis that variable host innate immune responses to GBS, which significantly impact pathogenesis, stem in part from genotypic and phenotypic differences among GBS isolates. These and similar studies may inform the development of improved diagnostic, preventive, or therapeutic strategies targeting invasive GBS infections.
Topics: Bacterial Capsules; Biomarkers; Disease Susceptibility; Host-Pathogen Interactions; Humans; Immunity, Innate; Macrophages; Signal Transduction; Streptococcal Infections; Streptococcus agalactiae; Stress, Physiological; THP-1 Cells
PubMed: 33558317
DOI: 10.1128/IAI.00647-20 -
Microbiology (Reading, England) Jul 2021Capsular polysaccharides (CPSs) protect bacteria from host and environmental factors. Many bacteria can express different CPSs and these CPSs are phase variable. For...
Capsular polysaccharides (CPSs) protect bacteria from host and environmental factors. Many bacteria can express different CPSs and these CPSs are phase variable. For example, ) is a prominent member of the human gut microbiome and expresses eight different capsular polysaccharides. Bacteria, including , have been shown to change their CPSs to adapt to various niches such as immune, bacteriophage, and antibiotic perturbations. However, there are limited tools to study CPSs and fundamental questions regarding phase variance, including if gut bacteria can express more than one capsule at the same time, remain unanswered. To better understand the roles of different CPSs, we generated a CPS1-specific antibody and a flow cytometry assay to detect CPS expression in individual bacteria in the gut microbiota. Using these novel tools, we report for the first time that bacteria can simultaneously express multiple CPSs. We also observed that nutrients such as glucose and salts had no effect on CPS expression. The ability to express multiple CPSs at the same time may provide bacteria with an adaptive advantage to thrive amid changing host and environmental conditions, especially in the intestine.
Topics: Bacterial Capsules; Bacteroides thetaiotaomicron; Gastrointestinal Microbiome; Humans; Polysaccharides, Bacterial
PubMed: 34224345
DOI: 10.1099/mic.0.001066