Revising the role of the pneumococcal vex-vncRS locus in vancomycin tolerance

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Multidrug-resistant Streptococcus pneumoniae infections are increasing.
• Vancomycin is a critical treatment, but strains exhibiting tolerance, not resistance, pose a challenge.
• The vex123-pep27-vncRS locus was previously implicated in vancomycin tolerance.

Purpose of the Study:

• To investigate the role of the vex123-pep27-vncRS locus in vancomycin tolerance in Streptococcus pneumoniae.
• To clarify the mechanisms underlying vancomycin tolerance in this pathogen.
• To identify factors influencing bacterial autolysis and tolerance.

Main Methods:

• Genetic manipulation of Streptococcus pneumoniae strains to create mutants (e.g., vex3 mutant).
• Phenotypic analysis of vancomycin tolerance in wild-type and mutant strains.
• Assessment of bacterial autolysis under various conditions.
• Microarray analysis to identify gene expression changes.

Main Results:

• Erythromycin in growth media induces a vancomycin-tolerant phenotype.
• Loss of Pep27 or VncRS function did not affect autolysis.
• A role for the vex123 ABC transporter in vancomycin tolerance was confirmed; vex3 mutants showed increased tolerance.
• The orientation of the resistance cassette influenced the tolerance phenotype.
• Microarray data suggested additional genes involved in tolerance in the vex3 mutant.

Conclusions:

• The vex123-pep27-vncRS locus's precise function and regulation require further determination.
• Erythromycin, bacterial capsule, LytA, and vex3 gene products are identified as factors influencing Streptococcus pneumoniae autolysis and vancomycin tolerance.