Streptococcus bovis new taxonomy: does subspecies distinction matter?

Area of Science:

• Microbiology and Infectious Diseases
• Clinical Diagnostics
• Genetics and Genomics

Background:

• Bacteremia caused by Streptococcus bovis/equinus complex is historically linked to significant comorbidities.
• Previous classifications of S. bovis have been updated, necessitating a re-evaluation of clinical associations.
• Understanding subspecies is crucial for accurate risk stratification and patient management.

Purpose of the Study:

• To determine the clinical significance of Streptococcus bovis/equinus complex subspecies based on updated nomenclature.
• To evaluate the diagnostic performance of MALDI-TOF mass spectrometry (MS) for subspecies identification.
• To assess the association of different subspecies with colorectal lesions (CL) and infective endocarditis (IE).

Main Methods:

• Reculturing and identification of historical S. bovis blood isolates using 16S rRNA gene sequencing and MALDI-TOF MS.
• Clinical data review of bacteremic patients (≥18 years) from 2002-2013.
• Systematic review of four recent case series to aggregate data on S. bovis/equinus complex bacteremia.

Main Results:

• Forty isolates were identified: 26 S. gallolyticus ssp. pasteurianus, 6 S. gallolyticus ssp. gallolyticus, 2 S. gallolyticus ssp. macedonicus, and 6 S. infantarius.
• MALDI-TOF MS demonstrated high accuracy (100%) for species identification and 83% for subspecies confirmation.
• In the study cohort, 59% of patients had IE and 20% had CL; aggregated data showed 28% with CL and 21% with IE across 320 cases.
• All identified subspecies were associated with either CL or IE.

Conclusions:

• The updated nomenclature for Streptococcus bovis/equinus complex is clinically relevant, with all subspecies associated with IE and CL.
• MALDI-TOF MS is a reliable and efficient method for species identification in routine clinical practice.
• Species-level diagnosis using MALDI-TOF MS should prompt further investigation for IE and CL.