In the optochin test, S. In the bile solubility test, sodium deoxycholate will lyse the pneumococcal cell wall, so it is demonstrated that S. Pneumococcus has several virulence factors including polysaccharide capsule Cpswhich is the main component, pneumolysin toxin, surface protein, and enzymes Figure 1 7. Recently, there are 97 serotypes of pneumococcus which are identified based on the antigenic and biochemical characteristics of Cps.
Several methods, i. Quellung test, latex agglutination test, and nucleotide sequencing test, are used to detect the serotype of pneumococcus. When serotypes are identifiable, they are known as a typable capsule.
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On the contrary, the non-typable capsule Figure 1 Virulence factors of S. Pathogenesis, treatment, and prevention of pneumococcal pneumonia. Lancet ; Pneumococcal serotypes are also divided into two groups based on their ability to overcome the immune response: colonization and invasive serotypes Colonization serotypes are resistant to non-opsonic neutrophils and cause NP carriage, but if they enter the lower airway, they will be destroyed by alveolar macrophage AM and complement system easily.
Invasive serotypes can be cleaned by neutrophils in the upper airway, but they are resistant to AM and complement system when they spread to the lower airway 6. Phase variation is one of the pneumococci capabilities to change its phenotype between transparent and opaque by increasing the encapsulation 11 Transparent phenotype that plays a role in colonization has a thin cell wall, low expression of the pneumococcal surface protein Psp -A, high expression of adhesin, choline-binding protein Cbp -A, and autolysin.
Conversely, opaque phenotype has a thick cell wall, high expression of Psp-A, low expression of Cbp-A, and resistance to opsonophagocytosis and is often found in circulation 13 Pneumococcal pneumonia Pneumococcal pneumonia is defined as pneumonia caused by S.
The incidences and serotype distributions vary through time and regions.
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Some factors may contribute to this condition such as vaccination programme, antibiotic use, socio-economic status, and the age of the population Pathogenesis NP colonization is an essential step towards pneumococcal disease including pneumococcal pneumonia. The link between pneumococcal carriage and disease is usually found in children.
A study by Greenberg et al. The rate of NP carriage in adults is lower than that in children However, contact with children may enhance adult carriage Mechanism of NP colonization of pneumococcus involves adherence of bacteria to epithelial cell via its receptors and activation of the host immune system.
In normal mucosa, the bacterial attachment is inhibited by local innate immunity such as saliva, cough reflex, and mucus layer. Then, the cilia movement will transfer bacteria out of the respiratory tract. The mucosa releases lysozyme, lactoferrin, and surfactant to limit bacterial growth 19 To survive from the mucosa barrier, pneumococci also produce several enzymes. They are neuraminidase, β-galactosidase, and β-N-acetylglucosaminidase that degrade mucus and inhibit mucociliary clearance.
Autolysin facilitates pneumolysin release to destroy the epithelial cells and reduce cilia movement.
Acta Microbiologica 34. (1987)
Cps and other pneumococcal proteins including Psp-A, Cbp-A, and enolase prevent complement deposition. Cbp-E inhibits neutrophil recruitment by degrading platelet-activating factor PAF. Furthermore, phosphorylcholine ChoPa component of teichoic acid in the bacterial cell wall, binds to PAF receptors, whereas Cbp-A binds to polymeric immunoglobulin receptor pIgRwhich is the secretory component of epithelial cells Figure 2 Figure 2 Mechanism of pneumococcal colonization in the respiratory tract.
Molecular surveillance on Streptococcus pneumoniae carriage in non-elderly adults; little evidence for pneumococcal circulation independent from the reservoir in children.
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Sci Rep ; In addition to mucosa that acts as the physical barrier of innate immunity, several cytokines and inflammatory mediators are released after pneumococci were recognized by antigen-presenting cells APCs. They play a role in the recruitment of leukocytes from the blood vessel into the mucosa of the respiratory tract. Mechanism of systemic innate immunity involves either the production of C-reactive protein or the activation of the complement system which stimulates polymorphonuclear PMN cells and macrophages in the opsonization of bacteria.
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Activation of the adaptive immune system consists of a local and systemic response. Pneumococci initiate mucosa-associated lymphoid tissue to produce immunoglobulin Ig -A which prevents bacteria invasion to mucosa membranes.
Then, both B cell and T cell are activated as part of the systemic what diseases are caused by alpha toxin immune response. Systemic antibodies such as anti-capsular polysaccharide and anti-protein pneumococcal antibody will be produced as the response to pneumococcal colonization. Most of the carriage is asymptomatic until pneumococcal clearance is completed 20 Pneumococcal pneumonia occurs after either bacterial aspiration or inhalation of droplet nuclei is presented Bacterial load, synergism effect between viral and pneumococcal infection, the morphology of Cps, and host immune defence influence the onset of disease The AM only has the ability to phagocyte a small number of pneumococci.
Furthermore, AM and epithelial cells release cytokines such as tumour necrosis factor TNF -α, interleukin IL -8, and chemokine CXC which activate neutrophil response, so they will migrate from the bloodstream to alveoli.
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After the process of phagocytosis, neutrophils become apoptosis. They will be followed by macrophage apoptosis that declines TNF-α expression; thus, it reduces neutrophil migration. These dead cells are removed by macrophages efferocytosis, and the resolution phase is begun 615 Adaptive immunity is also critical to the host response to pneumococci.
B cells produce Ig that is required for opsonophagocytosis process. Following the resolution phase, memory T cells still persist in alveoli 615 Diagnosis The clinical features of pneumococcal pneumonia are similar to other forms of typical pneumonia.
The symptoms are fever, malaise, productive cough, shortness of breath, and pleuritic pain. The sputum may be seen as rusty red colour or contains streaks of blood In geriatric patients, pneumococcal pneumonia symptoms are unspecified Sometimes, extrapulmonary signs such as meningitis, sepsis, peritonitis, and mastoiditis emerge earlier than pneumonia signs Radiological findings in pneumococcal pneumonia include infiltrating in one or several segments of a lobe, lobar consolidation, air bronchogram, and pleural effusion 22 Etiological diagnosis of pneumococcal pneumonia may be established through either conventional or molecular methods.
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Conventional methods include Gram staining, sputum, and blood or pleural fluid culture. Gram stain of sputum could be strongly suggestive of pneumococcal pneumonia if it shows the papilomul crește of Gram-positive diplococci and fulfils Bartlett criteria, i.
The limitations of Gram staining are inadequate sputum collection, antibiotic administration before specimen collection, and availability of skilled analyst. A false negative result is related to inadequate sampling, delayed processing of specimen, and antibiotic therapy before obtaining the specimen. A false positive result is often found in NP carriage, mainly among children; therefore, the result of sputum culture should be interpreted with Gram staining A definite diagnosis of pneumococcal pneumonia is determined if S.
The rate of a positive result in blood or pleural fluid culture is low. Pneumonia without bacteraemia, autolysis in the stationary phase, prior to an antibiotic, the inadequate sample volume are factors that influence the result of blood and pleural fluid culture.
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The limitation of a conventional method to detect pneumococcus is what diseases are caused by alpha toxin false negative result and it needs several days for culture procedures. The molecular method is developed to discover pneumococci quickly, and by using this method the administration of antibiotic does not impact the result.
- Pneumococcal pneumonia and invasive pneumococcal disease: immunopathogenesis and diagnosis
- Through the new techniques and establishment of novel protocols, especially in the field of molecular biology, together with the results from in vitro, in vivo preclinical and clinical studies carried out on an impressive number of patients with various pathologies, scientists have established ample associations between the microbiome composition and certain cancers or the treatment response.
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- Pot apărea condiloamele după tratament
These tests include teichoic acid C-polysaccharide detection, Cps detection, and nucleic acid amplification test IPD Meningitis, bacteraemia, parapneumonic pleural effusion, and empyema are types of IPD which present in two conditions. First, the host is colonized by serotype that is never recognized by the immune system before.