Genetic background affects stability of mecA in Staphylococcus aureus

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• The methicillin resistance determinant, mecA, is found on the staphylococcal cassette chromosome mec (SCCmec).
• SCCmec's natural distribution is confined to specific methicillin-resistant Staphylococcus aureus (MRSA) clonal complexes.
• Previous research suggests certain genetic backgrounds restrict mecA and penicillin-binding protein 2a expression.

Purpose of the Study:

• To investigate the role of the host chromosome in mecA transformability and expression.
• To assess the relationship between genetic background and mecA stability and expression in methicillin-susceptible S. aureus (MSSA).

Main Methods:

• Introduced the mecA gene on a plasmid (pYK20) into 103 MSSA clinical isolates.
• Classified MSSA isolates into 'major' MRSA or 'other' lineages based on prior multilocus sequence typing.
• Assayed nafcillin resistance phenotype via population analysis to evaluate mecA expression and plasmid stability.

Main Results:

• Strains from major MRSA lineages demonstrated higher transformability with the pYK20 plasmid.
• These major lineages were more efficient at maintaining the plasmid and expressing mecA-mediated resistance.
• Isolates from 'other' lineages showed reduced transformability, plasmid maintenance, and resistance expression.

Conclusions:

• Host chromosome genetic factors play a significant role in the transformability and expression of mecA.
• These permissive genetic factors contribute to the limited clonal distribution of SCCmec in nature.
• The study supports the hypothesis that specific S. aureus genetic backgrounds facilitate mecA acquisition and expression.