GeneXpert captures unstable methicillin-resistant Staphylococcus aureus prone to rapidly losing the mecA gene

Area of Science:

• Microbiology
• Molecular Biology
• Clinical Diagnostics

Background:

• Accurate identification of methicillin-resistant Staphylococcus aureus (MRSA) is crucial for effective treatment and infection control.
• Standard diagnostic methods may face challenges with certain MRSA strains.

Observation:

• A cefoxitin-susceptible Staphylococcus aureus strain was initially identified as MRSA using the Cepheid GeneXpert system.
• This specific MRSA strain exhibited high instability, rapidly losing its SCCmec genetic element during in vitro subculturing.

Findings:

• The observed instability highlights a limitation in identifying certain MRSA strains with conventional susceptibility testing.
• Rapid loss of SCCmec suggests that the genetic basis for methicillin resistance can be transient in some S. aureus isolates.

Implications:

• Gene amplification-based methods, such as those used by the GeneXpert, are superior for detecting unstable MRSA.
• These findings underscore the importance of utilizing molecular diagnostic tools for accurate and timely MRSA detection, especially in cases of suspected instability.