Streptococcus pneumoniae pneumonia

Still a serious disease: Despite advances in antibiotic therapy, and despit e the emergence of beta-lactam-resistant strains, mortality of pneumococcal pneumonia has remained relatively unchanged. The pathogenicity of a pneumo coccal strain results from an interaction between a specific host with its own capacity to "resist or yield" to the multiple virulence factors intrins ic to each S. pneumoniae strain. Role of the capsule: The capsule is the pneumococci's principal arm of resi stance against the host's defense systems. There is a wide variability depe nding on the capsule serotype. Inversely, the capsule plays no role in trig gering the inflammatory reaction which is secondary to substances released from the bacterial wall such as teichoic acid and peptidoglycan. Host response: The molecular mechanisms of cellular activation and inductio n of proinflammatory cytokins triggered by S. pneumoniae follow similar pat hways which are different from those for endotoxin triggered by Cram negati ve bacteria. Perspectives: A better understanding of the clinical expression, distinguis hing simple nasopharyngeal carriage from bacterial pneumonia should lead to the design of new therapeutic agents which will reduce the capacity of cer tain S. pneumoniae strains to invade the host and trigger deleterious infla mmatory reactions.