A brief history of the pneumococcus in biomedical research.

Because of its importance in human disease, Streptococcus pneumoniae has been the subject of intensive study at both the clinical and basic scientific levels for more than a century. In a number of instances, important advances in basic biology have resulted. Among these are the development of Gram's stain for identification of bacteria in patient specimens, investigations of the role of the bacterial capsule in resistance to phagocytosis by cells of the host immune system, demonstration that molecules other than proteins are capable of eliciting host humoral immune responses, development of safe and effective vaccines composed of isolated bacterial exopolysaccharides, confirmation of the efficacy of penicillin against serious gram-positive infections, and perhaps most important confirmation that DNA alone encodes genetic information.