The study of the diseases then caused is important both in terms of treatment and in terms of contributing to our understanding of the mechanisms by which the normal microflora usually interacts with the host. For a variety of reasons, however, this interaction can be disturbed and often results in the microflora becoming pathogens. The mechanisms by which this co-existence is achieved are still not properly understood and the interaction between the normal microflora and the host is far from simple. This normal microflora usually co-exists relatively peacefully with the host and does not cause infection. catarrhalis resides intracellularly in lymphoid tissue, providing a potential reservoir for persistence in the human respiratory tract.It has been estimated that there are more microbial cells inhabiting the human body than there are eukaryotic cells of which it is made up. However, the bacterium is now known to invade multiple cell types, including bronchial epithelial cells, small airway cells, and type 2 alveolar cells. catarrhalis has long been viewed as an exclusively extracellular pathogen. The presence of several adhesin molecules with differing specificities for various host cell receptors reflects the importance of adherence to the human respiratory epithelial surface in the pathogenesis of infection. Strains that cause infection in children differ in several phenotypic characteristics from strains that cause infection in adults, in whom the most common clinical manifestation is lower respiratory tract infection in the setting of chronic obstructive pulmonary disease. The species is composed of complement-resistant and complement-sensitive genetic lineages, the complement-resistant strains being more strongly associated with virulence. catarrhalis differ in their virulence properties. Similar shifts in etiology are being observed in children with sinusitis as well. These changes in colonization patterns may account for the increased rates of otitis media due to nontypable H. A relative increase in colonization by non-vaccine pneumococcal serotypes, nontypable H. The widespread use of pneumococcal polysaccharide vaccines in some countries has resulted in alteration of patterns of nasopharyngeal colonization in the population. Understanding nasopharyngeal colonization patterns is important, because the pathogenesis of otitis media involves migration of the bacterium from the nasopharynx to the middle ear via the eustachian tube.
The prevalence of colonization steadily decreases with age. Several factors likely account for this variability among studies, including living conditions, daycare attendance, hygiene, environmental factors (e.g., household smoking), and genetics of the population. On the basis of monthly or bimonthly cultures, colonization during the 1st year of life may range from 33% to 100%. Some geographic variation in rates of colonization is observed. Common throughout infancy, nasopharyngeal colonization is a dynamic process with active turnover due to acquisition and clearance of strains of M. Age is the most important determinant of the prevalence of upper respiratory tract colonization. The bacterium has not been recovered from animals or environmental sources. catarrhalis is the human respiratory tract. catarrhalis causes recurrent infections, which generally represent re-infection by new strains. Genetic and antigenic differences among strains account for the observation that resolving an infection by one strain does not induce protective immunity to other strains. catarrhalis is relatively conserved among strains only 3 serotypes (A, B, and C) that are based on oligosaccharide structure have been identified. In contrast to other gram-negative respiratory pathogens, such as Haemophilus influenzae and Neisseria meningitidis, the lipo-oligosaccharide of M. catarrhalis endotoxin lacks repeating polysaccharide side chains and is thus a lipo-oligosaccharide. Several outer membrane proteins demonstrate sequence differences among strains, particularly in regions of the proteins that are exposed on the bacterial surface. Substantial genetic heterogeneity exists among strains of M. On the basis of more modern analyses of genetic relatedness, Moraxella catarrhalis is now the accepted name. Initially named Micrococcus catarrhalis, its name was changed to Neisseria catarrhalis in 1970 because of its phenotypic similarities and similar ecological niche with commensal Neisseria species. catarrhalis has long been considered to be an upper respiratory tract commensal.
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