Fc fragment. For successful acquisition in a new host, pneumococcus must successfully adhere to the mucous membrane of the new host’s nasopharynx. Pneumococcus is able to evade detection by the mucous membrane when there is a higher proportion of negatively charged capsules. This clearance is mediated by Immunoglobulin A1 (IgA1) which is abundant on the URT mucosal surfaces. Colonization Transparent and opaque colony morphology has been observed for pneumococci. Airway colonization is observed in transparent phenotypes of serotypes, while survival in bloodstreams is observed for opaque phenotypes. Colonizable strains exhibit resistance against neutrophilic immune response. Successful colonization requires S. pnuemoniae to evade detection by the nasal mucus and attach to epithelial surface receptors. Asymptomatic colonization occurs when S. pneumoniae bind to N-acetyl-glucosamine on epithelium without inflammation. However, co-infection with a pre-existing inflammatory URT infection results in an over-expression of the epithelial receptors utilized by S. pneumoniae, thus increasing the likelihood of colonization. Neuraminidase also increases instances of epithelial binding through its cleavage of N-acetylneuraminic acid, glycolipids, glycoproteins, and oligosaccharides. Invasion Initial colonization of the nasopharynx is typically asymptomatic, but invasion occurs when the bacteria spreads to other parts of the body including the lungs, blood, and brain. Interactions between Phosphorylcholine (ChoP) components on colonized epithelial cells allow for docking of choline binding proteins (CBPs), most notably CbpA. Colonization of the respiratory tract, and thus pneumonia cannot occur without CpbA. The pneumococcus moves across the mucosal barrier by integrating itself with the polymeric immunoglobulin receptor (pIgR), which is used by mucosal epithelial cells to transport IgA and IgM to the apical surface. Following its cleavage at the apical surface, pIgR, and subsequently the pneumococcus, move back to the basolateral surface allowing invasion of the upper respiratory tract. The pneumococcus then moves to invade the lower respiratory tract, evading the mucociliary escalator with the assistance of neuraminidase. References Pneumonia Bacterial diseases