Misidentification of vancomycin-resistant Staphylococcus aureus as coagulase-negative Staphylococcus

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Resistance

Background:

• Reduced vancomycin susceptibility in Staphylococcus aureus is linked to biological changes like altered coagulase activity and cell wall thickening.
• The impact of these biological changes on routine identification methods for Staphylococcus aureus has not been well-documented.

Purpose of the Study:

• To investigate whether biological alterations in vancomycin-susceptibility-reduced coagulase-negative staphylococci (CoNS) affect their identification by standard laboratory techniques.
• To assess the potential for these altered strains to revert to a vancomycin-susceptible phenotype.

Main Methods:

• Utilized PCR to detect Staphylococcus aureus-specific genes (nuc, coa, 16S rRNA) in 24 vancomycin-susceptibility-reduced CoNS strains.
• Involved serial passaging of identified strains on nutrient agar without vancomycin to observe for phenotypic reversion.
• Employed automated testing methods for identification of revertant isolates.

Main Results:

• Six isolates initially identified as Staphylococcus haemolyticus tested positive for Staphylococcus aureus-specific genes (nuc, coa, 16S rRNA).
• These six strains reverted to vancomycin-susceptible forms after serial passaging.
• Revertant isolates were confirmed as Staphylococcus aureus using automated identification methods.

Conclusions:

• Biochemical changes in Staphylococcus aureus strains with reduced vancomycin susceptibility can complicate their identification.
• Routine diagnostic methods may require enhanced attention and improved techniques to accurately detect these evolving strains.
• The potential for phenotypic reversion in altered Staphylococcus aureus strains necessitates careful consideration in clinical settings.