Observations on emergence of mannitol-use-deficient Staphylococcus aureus

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Clinical Infectious Diseases

Background:

• Staphylococcus aureus clones typically emerge and recede on a decadal cycle.
• Virulence factors can drive clonal continuation, influencing bacterial evolution.
• Standard S. aureus isolates form yellow colonies on mannitol salt agar.

Purpose of the Study:

• To investigate a newly emergent clone of Staphylococcus aureus with distinct phenotypic characteristics.
• To understand the genetic basis and virulence profile of this novel S. aureus clone.
• To assess the clinical implications and potential misidentification of this emerging clone.

Main Methods:

• Phenotypic characterization of clinical S. aureus isolates on mannitol salt agar.
• Genetic analysis to identify mutations in the mannitol fermentation pathway.
• Assessment of virulence factor expression into stationary phase.
• Comparative analysis of inflammatory properties with known S. aureus strains.

Main Results:

• A novel S. aureus clone emerged post-2020, exhibiting intensely pink colonies on mannitol salt agar.
• This hyper-pink clone lacks the mannitol-1-phosphate dehydrogenase gene, impairing mannitol fermentation.
• The clone exhibited sustained expression of cell-surface and secreted virulence factors into the stationary phase.
• Hyper-pink S. aureus isolates showed pro-inflammatory properties similar to USA300 and USA400 strains.

Conclusions:

• A new S. aureus clone selected for its inability to ferment mannitol has emerged.
• The hyper-pink phenotype and prolonged virulence factor production are key characteristics of this clone.
• This clone, found in patients with atopic dermatitis, may be misidentified as coagulase-negative staphylococci.