English: Streptococcus pneumoniae isolated from blood culture bottle (A) and nasal swab (B). On sheep blood agar, pneumococci grow as 1-2 mm glistening colonies surrounded by a zone of alpha-hemolysis (A, B, C, D, E, F). Another characteristic feature of S.pneumoniae is the central navel-like depression of the colonies that is caused by the pneumococcal autolysin (G). Due to the production of capsular polysaccharide, colonies appear moist. Colonies may be large and mucoid if large amounts of polysaccharide are made (B, C, I). Most isolates are optochin susceptible (H). In blood culture specimens, S.pneumoniae tends to form chains of varying lengths, similar to other streptococci.