Methicillin-Resistant Staphylococcus aureus Blood Isolates Harboring a Novel Pseudo-staphylococcal Cassette...

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in both community and healthcare settings.
• The staphylococcal cassette chromosome mec (SCCmec) element is crucial for MRSA's methicillin resistance.
• Understanding novel SCCmec variants is vital for tracking MRSA evolution and spread.

Purpose of the Study:

• To characterize a newly identified pseudo-SCCmec (ΨSCCmec) element in MRSA blood isolates.
• To investigate the genetic makeup and potential implications of this novel element.
• To assess the evolutionary significance of ΨSCCmec in MRSA.

Main Methods:

• Isolation and identification of MRSA from blood specimens.
• Antimicrobial susceptibility testing using disk diffusion.
• SCCmec typing via multiplex polymerase chain reaction (PCR).
• Whole genome sequencing using single molecule real-time (SMRT) technology.

Main Results:

• Two MRSA isolates (E16SA093 and F17SA003) with sequence type 72 and agr-type I were identified.
• Both isolates possessed a novel SCCmec IV-like element lacking the cassette chromosome recombinase (ccr) gene complex, termed ΨSCCmec.
• This ΨSCCmec element resulted from the deletion of the ccr complex and adjacent chromosomal DNA.

Conclusions:

• The identified ΨSCCmec element, lacking the ccr gene complex, is likely non-mobile, representing a potential evolutionary adaptation.
• The absence of mobility genes may confer a selective advantage, influencing MRSA's evolutionary trajectory.
• Close monitoring of MRSA clones carrying this ΨSCCmec element is recommended due to potential dissemination.