Abstract

Streptococcus pneumoniae (the pneumococcus) is the most common bacterial respiratory pathogen in the United Kingdom, causing pneumonia, septicaemia and meningitis. The pneumococcus is responsible for between 60-75% of community acquired pneumonia in the UK, resulting in mortality rates of over 20% for those with concurrent pneumococcal septicaemia. Worldwide, the situation is worse, with pneumococcal septicaemia the major cause of infant mortality in developing countries, causing approximately 25% of all preventable deaths in children under the age of 5, and an annual burden of over 1.2 million infant deaths. The pneumococcus is particularly well adapted to colonising the mucosal surfaces of the nasopharynx and the combination of bacterial virulence factors, together with the ability to evade early host immune components, allows the pneumococcus to spread from the upper respiratory tract to sterile regions of the lower respiratory tract, leading to pneumonia. In this seminar we shall discuss in vivo models of long-term nasopharyngeal carriage and models of acute and chronic pneumonia. The role of virulence factors such as pneumolysin will be discussed as will the response of host immunity to such events.