Host-pathogen interaction during Streptococcus pneumoniae colonization and infection

Abstract

Streptococcus pneumoniae was discovered by Sternberg and Pasteur in 1880. It took another six years to discover that this microorganism, called the pneumococcus, was the actual cause of bacterial pneumonia . Subsequently, this bacterium has been shown to provoke an impressive number of diseases, which can be roughly classified in respiratory and invasive. Respiratory diseases by S. pneumoniae are sinusitis, otitis media, bronchitis and pneumonia, of which the latter one may be complicated by septicemia . Disseminated invasive infections caused by the pneumococcus include sepsis, meningitis, endocarditis and arthritis. Morbidity and mortality are high both in the developing and the developed world: annually 3 million people die worldwide of pneumococcal infections. Approximately 1 million are children under the age of five years . Risk groups for pneumococcal disease are children younger than 2 years, elderly people and immunocompromised patients . In children, the increased risk for pneumococcal infections is mainly due to a relatively immature immune response to type II T-cell independent (TI-2) antigens such as capsular polysaccharides . In the elderly, the ability of both the innate as well as the adaptive immunity to respond to pneumococcal infection are thought to decline . In addition, higher rates of pneumococcal invasive diseases have been observed among populations such as Alaskan Natives, American Indians and African Americans . Patient groups who are at risk for particular variants of pneumococcal diseases are well defined. For example functional asplenia as in sickle cell disease as well as anatomic asplenia are serious risk factors for pneumococcal sepsis. This is due to the absence or dysfunction of the spleen, which is involved in systemic clearance of S. pneumoniae. In addition, complement deficiency and lower levels of circulating antibodies are thought to contribute to the increased susceptibility to pneumococcal infections in patients with sickle cell disease and other haemoglobinopathies . A relatively new risk group for pneumococcal meningitis are children with a cochlear implantation . Disease in these patients is thought to occur by the presence of a continuum between the outer ear and the inner skull. In general, patients with cerebrospinal fluid leakage, immunodeficiencies, chronic cardiovascular and pulmonary disease, HIV infections and diabetes mellitus are considered at risk for pneumococcal invasive disease.