Abstract
Purpose:
Purpose: Streptococcus pneumoniae is a prevalent cause of bacterial conjunctivitis, especially in children. One bacterial lineage in particular, ST448, has caused multiple outbreaks of conjunctivitis and was recently shown by our group to be a major contributor to non-outbreak related ocular infections throughout the US. These findings suggest that some lineages of S. pneumoniae possess a unique ocular tropism and are capable of spawning epidemics. In the present study we set out to sequence representative strains isolated from three major outbreaks to begin to identify candidate functions these outbreak strains possess that potentially contribute to the ability to cause epidemic conjunctivitis, and account for their unusual tropism.
Methods:
Methods: Genomes of 6 S. pneumoniae isolates from conjunctival infection (two each from outbreaks in New Hampshire, Maine and Minnesota) were sequenced, assembled and compared to the genomes of other S. pneumoniae from other types of infection.
Results:
Results: Comparative analysis shows that ST448 strains possess only about 80% of the gene content of TIGR4. Absent from ST448 are genes for capsular biosynthesis and surrounding genetic elements, as well as ~ 25kb of the TIGR4 genome putatively encoding a cell wall surface anchor protein, sortases, a transcriptional regulator and cellobiose biosynthesis machinery. Metabolic reconstruction of the ST448 draft genome and comparison to TIGR4 indicates that various metabolic subsystems do not occur in ST448. Additonally, several bacteriocin operons also were not found. ST448 includes an additional 360kb of sequence, with about 1/3 of that related to more distant S. pneumoniae strains, and the remainder being derived from either non-pneumococcal species or lacking nucleotide homology to any other genes in GenBank.
Conclusions:
Conclusion: The genome landscape content of an ST448 strain is substantially different from even the nearest strain, and possesses a number of genes with the potential to contribute to its prevalence in outbreak and non-outbreak infections and tropism for the ocular surface of sequence type 448 S. pneumoniae.
Keywords: 539 genetics •
475 conjunctivitis •
464 clinical (human) or epidemiologic studies: risk factor assessment