Oral Presentation BACPATH 2022

Streptococcus pneumoniae strains isolated from a single paediatric patient display distinct phenotypes. (#42)

Hannah N Agnew 1 , Erin B Brazel 1 , Alexandra Tikhomirova 2 , Kimberley T McLean 1 , John M Atack 3 , Mark van der Linden 4 , James C Paton 1 , Claudia Trappetti 1
  1. Department of Molecular and Biomedical Science, The University of Adelaide, Adelaide, South Australia, Australia
  2. Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
  3. Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
  4. German National Reference Center for Streptoccocci, University Hospital RWTH Aachen, Aachen, Germany

Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacterium that can switch from asymptomatically colonising the human nasopharynx to cause diseases such as otitis media, pneumonia, bacteriaemia and meningitis, by invading the ears, lungs, blood and brain, respectively. The mechanisms by which pneumococci are able to spread to the different anatomical niches and cause disease are poorly understood. This is mainly due to large genetic variations between strains, with over 100 capsular serotypes superimposed on more than 16,000 sequence types.

To overcome the genetic diversity issues, I have used blood and cerebral spinal fluid (CSF) S. pneumoniae strains (serotype 15C sequence type 8711) isolated from a single paediatric meningitis patient. These strains were characterised in in vitro and in vivo assays. I found that the blood isolate has a major defect in the ability to metabolise raffinose and reduced transcription of raffinose utilisation genes, compared with the CSF strain. The fitness of these strains was then assessed in vivo using a murine intranasal infection model. I discovered that the isolates displayed different niche adaptation, with only the CSF isolate spreading to the ear of the infected mice. Preliminary genetic analyses have found a difference between the blood and CSF strains in the rafS gene, responsible for repression of the alpha-galactosidase gene, which cleaves raffinose into galactose and sucrose. Moreover, initial analysis of the phasevarion of pneumococci strains isolated from different niches demonstrates that this system phase-varies to different alleles commensurate with the initial source of the isolate. Further work is needed to demonstrate if this switching results due to differential epigenetic regulation.

Together, these studies display that strains of the same clonal lineage isolated from the blood and CSF of a single paediatric meningitis patient have distinct in vitro and in vivo phenotypes. Exposure of the pneumococci to markedly different microenvironments, to which the organism must adapt during disease progression, may explain the genetic and phasevarion differences observed in this study.