Invasive Streptococcus oralis Expressing Serotype 3 Pneumococcal Capsule, Japan

Area of Science:

• Microbiology
• Genomics
• Infectious Diseases

Background:

• Streptococcus oralis is an oral bacterium.
• Invasive infections by S. oralis are rare but can be severe.
• Serotype 3 pneumococcal capsule is typically associated with Streptococcus pneumoniae.

Purpose of the Study:

• To investigate the genetic basis of invasive disease caused by Streptococcus oralis in Japan.
• To characterize the unique features of the S. oralis strains involved in these cases.

Main Methods:

• Clinical case reporting of two adult patients with invasive disease.
• Whole-genome sequencing of the causative S. oralis isolates.
• Comparative genomic analysis to identify genetic elements.

Main Results:

• Both cases involved S. oralis expressing the serotype 3 pneumococcal capsule.
• The S. oralis strains formed mucoid colonies.
• Whole-genome sequencing identified identical recombination of the serotype 3 pneumococcal capsule locus and hyl fragment in two distinct S. oralis strains.

Conclusions:

• Streptococcus oralis can acquire and express the Streptococcus pneumoniae serotype 3 capsule.
• Genetic recombination events involving the capsule locus can contribute to the emergence of novel pathogenic strains.
• This finding highlights the potential for horizontal gene transfer to impact bacterial virulence and host adaptation.