# Population dynamics and recombination between Streptococcus pneumoniae strains in nasopharyngeal biofilms Open Access

## Brophy, Jennifer Erin (2016)

Permanent URL: https://etd.library.emory.edu/concern/etds/w9505112w?locale=en
Published

## Abstract

Invasive pneumococcal disease (IPD), caused by Streptococcus pneumoniae, is a leading cause of death among children worldwide. Asymptomatic nasopharyngeal colonization by S. pneumoniae, a prerequisite for IPD, is estimated to occur in up to 90% of healthy children. Recent studies have shown that 50% of colonized children carry more than one strain (co-colonization). Colonization is mediated by pneumococcal biofilms, which form on the nasopharyngeal epithelium. Nasopharyngeal biofilms may contribute to the emergence of antibiotic-resistant strains and new pneumococcal serotypes, thought to occur by genetic recombination in the human nasopharynx. The aims of this thesis were to study the population dynamics of two pneumococcal strains and to begin exploring pneumococcal nasopharyngeal recombination. We first examined two S. pneumoniae strains to determine whether some serotypes colonize the nasopharynx more effectively, i.e., produce more biofilms, and release more planktonic (i.e., invasive) pneumococci on human nasopharyngeal cells. Genome-sequenced reference strains, serotype 19F strain GA13499 and serotype 2 strain D39, were grown separately or together in bioreactors containing human nasopharyngeal cells for 24 h. GA13499 encodes resistance to trimethoprim whereas D39 carries resistance to tetracycline in a plasmid encoding the tetM gene. Therefore, blood agar plates with the appropriate antibiotics were used to compare viable biofilm cells and planktonic bacteria grown separately or together. Our results demonstrated that serotype 19F strain GA13499 produced more biofilms, and released more planktonic bacteria, than strain D39, either when grown alone or together with D39. The addition of the other strain did not significantly affect biofilm counts or counts of planktonic bacteria of either strain. We recovered recombinant pneumococci encoding resistance to both antibiotics. While we have a reason to believe they are 19F that acquired the tetM-encoding plasmid from strain D39, the direction of recombination and the mechanism governing the recombination direction needs to be further investigated. Should these recombinant pneumococci be 19F, the biofilm recombination frequency was 2.35 x 10-4 and the planktonic recombination frequency was 1.02 x 10-3.

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Works Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21