The Best of All Worlds: Streptococcus pneumoniae Conjunctivitis through the Lens of Community Ecology and Microbial Biogeography

Abstract

The study of the forces which govern the geographical distributions of life is known as biogeography, a subject which has fascinated zoologists, botanists and ecologists for centuries. Advances in our understanding of community ecology and biogeography—supported by rapid improvements in next generation sequencing technology—have now made it possible to identify and explain where and why life exists as it does, including within the microbial world. In this review, we highlight how a unified model of microbial biogeography, one which incorporates the classic ecological principles of selection, diversification, dispersion and ecological drift, can be used to explain community dynamics in the settings of both health and disease. These concepts operate on a multiplicity of temporal and spatial scales, and together form a powerful lens through which to study microbial population structures even at the finest anatomical resolutions. When applied specifically to curious strains of conjunctivitis-causing, nonencapsulated Streptococcus pneumoniae, we show how this conceptual framework can be used to explain the possible evolutionary and disease-causing mechanisms which allowed these lineages to colonize and invade a separate biogeography. An intimate knowledge of this radical bifurcation in phylogeny, still the only known niche subspecialization for S. pneumoniae to date, is critical to understanding the pathogenesis of ocular surface infections, nature of host-pathogen interactions, and developing strategies to curb disease transmission.

Population structure of ocular Streptococcus pneumoniae is highly diverse and formed by lineages that escape current vaccines

“…ECC strains carry a variety of gene clusters that are absent or substantially different in encapsulated strains from invasive infections, and are thought to play an important role in the pathogenesis of epidemic conjunctivitis. This bifurcation in phylogeny and hyper-niche specialization of ECC is thought to have been driven by selective forces present in the unique environment of the ocular surface wet mucosa, which may play a role in community assemblage and dynamics impacting the microscale biogeography of conjunctivitis [ 23 ].…”

Hospital-Associated Multidrug-Resistant MRSA Lineages Are Trophic to the Ocular Surface and Cause Severe Microbial Keratitis

“…These strains carry a set of genes that are absent or substantially different from those encoded within the genomes of encapsulated respiratory strains, which appear to be important for the pathogenesis of epidemic conjunctivitis. We have demonstrated that a unified model of microbial biogeography that incorporates classic ecological principles to explain community assemblage and dynamics can be applied to the understanding of this radical bifurcation in phylogeny and niche subspecialization of the unencapsulated S. pneumoniae conjunctivitis cluster (21). Because MRSA now rank among leading causes of a variety of ocular infections, to gain insight into particular features of importance in the pathogenesis of infection, it was of interest to determine the microscale biogeography of MRSA eye infections, whether dominant genetic lineages were associated with all sites of infection, or if there was evidence of a tissue tropism that would drive a specific population structure.…”