Streptococcus pneumoniae pneumonia

Still a serious disease: Despite advances in antibiotic therapy, and despite the emergence of beta-lactam-resistant strains, mortality of pneumococcal pneumonia has remained relatively unchanged. The pathogenicity of a pneumococcal strain results from an interaction between a specific host with its own capacity to "resist or yield" to the multiple virulence factors intrinsic to each S. pneumoniae strain. Role of the capsule: The capsule is the pneumococci's principal arm of resistance against the host's defense systems. There is a wide variability depending on the capsule serotype. Inversely, the capsule plays no role in triggering 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 induction of proinflammatory cytokins triggered by S. pneumoniae follow similar pathways which are different from those for endotoxin triggered by Cram negative bacteria. Perspectives: A better understanding of the clinical expression, distinguishing simple nasopharyngeal carriage from bacterial pneumonia should lead to the design of new therapeutic agents which will reduce the capacity of certain S. pneumoniae strains to invade the host and trigger deleterious inflammatory reactions.