Rapid identification, capsular typing and molecular characterization of Streptococcus pneumoniae by using whole genome nanopore sequencing

Background: Whole genome sequencing has emerged as a useful tool for identification and molecular characterization of pathogens. MinION (Oxford Nanopore) is a real-time third generation sequencer whose portability, affordability and speed in data production make of it an attractive device for whole genome sequencing. The objective of this study is to evaluate MinION sequencer for pathogen identification and molecular characterization of Streptococcus pneumoniae isolated at a children's Hospital. Whole genome sequencing of 32 Streptococcus pneumoniae invasive isolates, previously characterized by standard methods (Quellung reaction, Multiplex PCR and Sanger-MLST), were performed. DNA was extracted using ZymoBIOMICS DNA Microprep kit. Quantification and purity of DNA was assessed by Qubit and Nanodrop, respectively. Library preparation was performed using the Rapid Barcoding Kit. Real-time workflow EPI2ME platform "What's it in my pot" was used for species identification. Fast5 sequences were converted into FASTQ by Albacore software. Reads were assembled using CANU software. PathogenWatch, genomic epidemiology and pubmlst online tools were used for capsular typing and/or whole genome-MLST profile.

Results: Rapid identification of Streptococcus pneumoniae was achieved by "What's in my pot". Capsular typing was correctly assigned with PathogenWatch in all 32 isolates at serogroup level and 24 at serotype level. Whole genome-MLST results obtained by genomic epidemiology and pubmlst were consistent with double locus variant clonal complex obtained by Sanger-MLST in 31 isolates.

Conclusion: MinION sequencer provides a rapid, cost-effective and promising pathway for performing WGS by a pocked-sized device for epidemiological purposes but improving its sequencing accuracy will make it more appealing to be used in clinical microbiology laboratories.