Staphylococcal cassette chromosome mec containing a novel mec gene complex, B4

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Staphylococcus epidermidis is a common cause of bloodstream infections.
• Staphylococcal cassette chromosome mec (SCCmec) elements are crucial for methicillin resistance in staphylococci.
• Understanding SCCmec diversity is vital for infection control and treatment.

Purpose of the Study:

• To describe a novel subclass of the mec class B complex in Staphylococcus epidermidis.
• To investigate the genetic structure and evolution of SCCmec elements in clinical isolates.

Main Methods:

• Phenotypic antibiotic susceptibility testing was performed on S. epidermidis isolates.
• Whole-genome sequencing (WGS) was employed to analyze the genetic makeup of the isolates.
• Sequence analysis was used to identify and characterize SCCmec structures and mec complex organization.

Main Results:

• A new SCCmec subtype, designated SCCmec IVUMCG335, was identified, featuring plasmid pUB110 integrated into SCCmec IVc.
• A novel mec class B complex subclass, named B4, was discovered in isolate UMCG337, characterized by IS431-mediated inversion.
• Isolates UMCG335 and UMCG337 harbored composite islands containing restriction-modification and CRISPR-Cas systems.

Conclusions:

• IS431 plays a significant role in the evolutionary dynamics of the SCCmec region.
• The observed genetic diversity in SCCmec elements presents challenges for current typing methodologies.
• The findings underscore the need for updated SCCmec nomenclature to accommodate newly identified structures.