cells are spherical or elliptic (about 0.5–1.25 μm in diameter) and mostly arranged in pairs. They can occasionally be found in short chains or as single cells. Typical cells of this species are lanceted and arranged in pairs, and the extracellular capsule can be observed by capsule staining. However, cells can easily form chains after continuous culture. Cells of S. pneumoniae
are gram-positive but can change to be gram-negative when aged (Figure 5.4(A) and (B)
). S. pneumoniae
cells observed by SEM are shown in Figure 5.4(C)
. The GC content of the S. pneumoniae
genome is 30% (by Tm method) or 42% (by Bd method), and its type strain is NCTC7465.
is a kind of facultative anaerobe, but could generate a substantial amount of H2
under aerobic conditions. Growth of S. pneumoniae
requires a complex medium rich in nutrients, including blood, serum, or ascites, as well as vitamin B. Cells of this species grow well on BHI-blood agar plates, and form roof-like, reflective and smooth colonies or rugose, mycelium-like, rough colonies (Figure 5.4(D)
). Cells of S. pneumoniae
can generate a great deal of capsular polysaccharides and therefore often form sticky colonies (Figure 5.4(E)
). In fact, this capsular polysaccharide is the species-specific antigen and virulence factor of S. pneumoniae
. S. pneumoniae
cells observed by stereomicroscope are shown in Figure 5.4(F)
. The final pH value of a culture in glucose broth is pH 5.0. Compared to other streptococci, the addition of bile or cholate is required for the isolation and identification of S. pneumoniae.
carries out metabolic reactions through fermentation. Cells of this species can ferment glucose, galactose, fructose, sucrose, maltose, raffinose, and inulin to produce acid, and some strains can also ferment mannitol but not dulcite and sorbitol. Bacteriolysis of S. pneumoniae
cells by bile is positive, and this characteristic is helpful in distinguishing S. pneumoniae from other streptococci.