Nasal colonization with Streptococcus pneumoniae includes subpopulations of surface and invasive pneumococci

Abstract

We demonstrated that during colonization with Streptococcus pneumoniae the nasal mucosal tissues of mice support two populations of pneumococci. Transparent-phase pneumococci can be readily washed from the outer surface, while a second population composed of primarily opaque-phase pneumococci is released only by homogenization of the nasal tissue. The fact that the opaque phase has previously been associated with invasion and the fact that opaque-phase pneumococci were released by homogenization of previously washed nasal tissue suggest that the opaque-phase pneumococci may have invaded the nasal tissue. Consistent with this hypothesis was our observation that there was inflammation in portions of the nasal mucosa of the colonized mice but not in the mucosa of noncolonized mice, but this observation did not prove the hypothesis. If the opaque-phase pneumococci released from the nasal tissue were from within the tissue and/or if resistance of the opaque-phase subpopulation to antibody, complement, and phagocytes is essential for long-term carriage, it seems likely that the virulence factors of S. pneumoniae that are necessary for killing humans exist to facilitate carriage. Although this speculation is unproven, the observation that there are separate populations of pneumococci during colonization may help guide future attempts to understand the biology of nasal colonization by this pathogen.

FIG. 1.

Transparent and opaque colonies of strains TIGR4 (A) and L82016 (B) growing on TSA supplemented with cysteine. A “T” indicates transparent colonies. All other colonies were classified as opaque.

FIG. 2.

Nasal tissue from a noninoculated CBA/N mouse (A) and a mouse inoculated i.n. 6 days previously with 2.4 × 10⁶ CFU of EF3030 (B). Tissues were stained with hematoxylin and eosin and examined microscopically at a magnification of ×200. The tissue from the normal mouse is representative of all fields examined for the noninfected mouse. Most fields of infected tissue were similar to the field of tissue from the noninfected mouse. Panel B shows an inflamed area of the mucosa of a colonized mouse. Note the lack of cilia and the disorganization of the submucosal cells.

FIG. 3.

Nasal tissue from a noninoculated CBA/N mouse (A) and from mice inoculated i.n. 6 days previously with 2.4 × 10⁶ CFU of EF3030 (B to E). All fields were examined microscopically at a magnification of ×400 after staining with hematoxylin and eosin. (B) Acute inflammation of the mucosa with loss of cilia (arrow); (C) acute inflammation of mucosa and submucosa with the cilia preserved (arrow); (D) neutrophils filling a crypt in the mucosal surface; (E) scattered inflammatory cells (arrows) in the inflamed mucosa of a colonized mouse.