Functional mgrA Influences Genetic Changes within a Staphylococcus aureus Cell Population over Time

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Genetics

Background:

• Staphylococcus aureus can develop alternative cell types, including Small Colony Variants (SCVs), which are associated with persistent infections and antibiotic tolerance.
• SCVs are difficult to study due to phenotypic instability and reversion to normal cell types.
• Previous work identified SCVs with mutations in the transcription factor mgrA in prolonged continuous culture.

Purpose of the Study:

• To investigate the role of the mgrA gene in the selection and characteristics of Staphylococcus aureus SCVs.
• To understand the mechanisms driving SCV emergence and their impact on bacterial behavior.

Main Methods:

• Continuous culture of wild-type and ΔmgrA mutant Staphylococcus aureus strains.
• Assessment of SCV emergence rates and phenotypic characteristics (metabolism, antibiotic MIC, biofilm formation).
• Whole-genome sequencing to identify genetic mutations and rearrangements in SCVs.

Main Results:

• The ΔmgrA mutant strain showed a faster selection of SCVs compared to the wild type, with increased mutagenesis.
• mgrA-derived SCVs exhibited impaired metabolism, altered minimum inhibitory concentrations (MICs) to certain antibiotics, and enhanced biofilm formation.
• Genomic analysis revealed SNPs in glmM and xerC, along with rearrangements affecting antibiotic resistance and pathogenicity genes.

Conclusions:

• A direct link between mgrA deficiency and the SCV phenotype in Staphylococcus aureus is established.
• The study highlights mgrA's role in regulating mutagenesis and SCV emergence, providing insights into persistent infections.
• Findings suggest mgrA-derived SCVs possess traits contributing to infection persistence and may represent a target for novel therapeutic strategies.