Influence of bacterial interactions on pneumococcal colonization of the nasopharynx

Abstract

Streptococcus pneumoniae (the pneumococcus) is a common commensal inhabitant of the nasopharynx and a frequent etiologic agent in serious diseases such as pneumonia, otitis media, bacteremia, and meningitis. Multiple pneumococcal strains can colonize the nasopharynx, which is also home to many other bacterial species. Intraspecies and interspecies interactions influence pneumococcal carriage in important ways. Co-colonization by two or more pneumococcal strains has implications for vaccine serotype replacement, carriage detection, and pneumonia diagnostics. Interactions between the pneumococcus and other bacterial species alter carriage prevalence, modulate virulence, and affect biofilm formation. By examining these interactions, this review highlights how the bacterial ecosystem of the nasopharynx changes the nature and course of pneumococcal carriage.

Figure 1

Diagram of the nasopharynx and pathways to pneumococcal diseases. The nasopharynx lies directly posterior to the nasal cavity and superior to the oropharynx. The pneumococcus can spread from its home in the nasopharynx through the Eustachian tube to cause otitis media, to the sinus cavities to cause sinusitis, through the larynx to the lower respiratory tract to cause pneumonia, and then in some cases, bacteremia. Image adapted from an illustration by Patrick J. Lynch distributed under Creative Commons Attribution 2.5 License.

Figure 2

Streptococcus pneumoniae forms multicellular structures in vitro on top of human lung cells. (a) Scanning electron micrograph of pneumococcal cells in 8-h biofilms grown on top of human lung epithelial cells show bacterial cells connected by an extracellular matrix. (b) Confocal images of GFP-expressing S. pneumoniae biofilms demonstrate cells co-localizing with sialic acid residues (stained red) present on human lung epithelial cells (nuclei stained blue). The top image is an optical xy section and the bottom is an xz section.