Color enhanced scanning electron micrograph (SEM) of type 4 Streptococcus pneumoniae bacteria adherent to a pharyngeal epithelial cell. Belonging to the alpha group of Streptococcaceae, Streptococcus pneumoniae is a major human pathogen that causes lung infections that can develop as secondary infections which may spread to other parts of the body. There are about 100 different serotypes with a rise in antibiotic resistance.