A novel capsular typing method for <em>Streptococcus pneumoniae </em>using Minimum SNPs — ASN Events
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  2. Poster Session B
  3. A novel capsular typing method for Streptococcus pneumoniae using Minimum SNPs

A novel capsular typing method for Streptococcus pneumoniae using Minimum SNPs (#321)

Rachael E Rayner 1 , Louise M Hafner 1 , Flavia Huygens 1
  1. Queensland University of Technology, Brisbane, QLD, Australia

Purpose of Study

Streptococcus pneumoniae, a potentially deadly bacterium, has the ability to switch its protective polysaccharide capsule via the process of horizontal gene recombination. Termed “capsule switching”, this is problematic globally since this bacterium can evade the current pneumococcal vaccines (1). Determination of these capsule switches largely relies on the combination of traditional serotyping methods and bacterial fingerprinting methods e.g. Pulsed Field Gel Electrophoresis (PFGE) and Multi-Locus Sequence Typing (MLST). Serotyping and whole capsule sequencing are laborious and expensive. Multiplex PCR reactions have been developed for capsule identification but none have been tested on all 98 possible capsule types (2). This study aims to develop a novel capsule typing method applicable to all pneumococcal serotypes using a bioinformatics approach to identify polymorphic genes within the capsule sequence. Used in combination with a bacterial fingerprinting method, capsule switching could be determined.

Method

A total of 93 available S. pneumoniae capsule sequences from NCBI database were analysed using a Minimum SNPs bioinformatics program (3). The program could identify a minimum number of capsule genes that would characterise each capsule type. The capsule typing method was run in silico and then PCR was performed to demonstrate the application to Queensland clinical isolates of S. pneumoniae.

Results

In silico data analysis identified 28 capsule genes that could distinguish 34 serotypes, and 39 serogroups (Simpson’s Index of Discrimination = 0.9883). For Queensland, only 17 capsule genes were required to distinguish all the serogroups and 21 serotypes (out of 35 serotypes detected in Queensland). PCR demonstrated the absence/presence of the capsule genes which can be used to display a capsule type profile.

Conclusion

Identification of pneumococcal capsule switching is important, particularly in light of vaccine evasion. Our study has demonstrated differentiation of the majority of pneumococcal serogroups using a bioinformatics approach. The potential for this inexpensive and quick capsule typing method may enable the rapid detection of pneumococcal serotypes and capsule switching events worldwide.

  1. Johnston, C, N Campo, MJ Bergé, P Polard, J-P Claverys. Streptococcus pneumoniae, le transformiste. Trends in Microbiology, 2014. 22(3): 113-119.
  2. Jauneikaite, E, A Tocheva, J Jefferies, et al. Current methods for capsular typing of Streptococcus pneumoniae. Journal of Microbiological Methods, 2015. http://dx.doi.org/10.1016/j.mimet.2015.03.006
  3. Robertson, GA, V Thiruvenkataswamy, H Shilling, EP Price, F Huygens, FA Henskens, PM Giffard. Identification and interrogation of highly informative single nucleotide polymorphism sets defined by bacterial multilocus sequence typing databases. Journal of Medical Microbiology, 2004. 53(Pt 1): 35-45.
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