Serotype-Switch Variant of Multidrug-Resistant Streptococcus pneumoniae Sequence Type 271

Area of Science:

• Microbiology
• Genomics
• Infectious Diseases

Background:

• Streptococcus pneumoniae is a leading cause of bacterial infections worldwide.
• The emergence of multidrug-resistant (MDR) strains poses a significant public health threat.
• Vaccine-refractory serotypes can evade existing immunization strategies.

Purpose of the Study:

• To investigate the genomic basis of newly emerged invasive, multidrug-resistant Streptococcus pneumoniae isolates.
• To characterize the recombination event responsible for a serotype switch to vaccine-refractory capsular serotype 3.
• To identify the genetic elements within the donated fragment.

Main Methods:

• Whole-genome sequencing of three invasive Streptococcus pneumoniae isolates.
• Comparative genomic analysis to identify recombination events.
• Mapping of recombination sites and characterization of the donated DNA fragment.

Main Results:

• Discovery of three invasive, MDR Streptococcus pneumoniae isolates belonging to the successful sequence type 271 complex.
• Identification of a serotype switch to capsular serotype 3, a known vaccine-refractory type.
• Mapping revealed a 55.9-kb donated fragment containing the capsular polysaccharide synthesis locus (cps3), pbp1a, and other virulence factors.

Conclusions:

• A recombination event involving a large DNA fragment led to the emergence of vaccine-refractory, MDR Streptococcus pneumoniae serotype 3.
• This event highlights the dynamic nature of Streptococcus pneumoniae evolution and the potential for rapid adaptation.
• Understanding these recombination mechanisms is crucial for developing effective control strategies against invasive pneumococcal disease.