Nasopharyngeal Carriage: Spreading Disease, Introducing Infection

The nasopharynx appears to be the primary Streptococcus pneumoniae reservoir and the source for both horizontal spread and transition to infection, according to the results of a study published in the September 25, 2012, edition of mBio.

In pneumococcal and other bacterial diseases, it appears that it is more difficult to eradicate nasopharyngeal carriage than invasive disease. Colonizing pneumococci exist in highly structured antibiotic-resistant communities. During colonization, collaborating multicellular communities of pneumococci attach to the carrier’s mucosal epithelium. They produce a polymeric matrix, called a biofilm, which encases them and favors competence genes. This creates a supragene environment and affords the bacteria protection from the host’s hostile environment. They can persist even in the presence of antibiotics.

When mouse models were co-colonized with 2 strains of pneumococci carrying specific genetic markers, the bacteria underwent natural transformation—exchanging genetic information—that was ~10⁷-fold more efficient than that using a model in which the study subject has sepsis. The researchers attribute this to the biofilm’s stability.

Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.