Current types of staphylococcal cassette chromosome mec (SCC mec ) in clinically relevant coagulase-negative staphylococcal (CoNS) species.

Coagulase-negative staphylococci (CoNS) colonize human skin and mucosal membranes, which is why they are considered harmless commensal bacteria. Two species, Staphylococcus epidermidis and Staphylococcus haemolyticus belong to the group of CoNS species and are most frequently isolated from nosocomial infections, including device-associated healthcare-associated infections (DA-HAIs) and local or systemic body-related infections (FBRIs). Methicillin resistance, initially described in Staphylococcus aureus , has also been reported in CoNS species. It is mediated by the mecA gene within the staphylococcal cassette chromosome (SCC mec ). SCC mec typing, primarily using PCR-based methods, has been employed as a molecular epidemiological tool. However, the introduction of whole genome sequencing (WGS) and next-generation sequencing (NGS) has enabled the identification and verification of new SCC mec types. This review describes the current distribution of SCC mec types, subtypes, and variants among CoNS species, including S. epidermidis , S. haemolyticus , and S. capitis . The literature review focuses on recent research articles from the past decade that discuss new combinations of SCC mec in coagulase-negative Staphylococcus . The high genetic diversity and gaps in CoNS SCC mec annotation rules underscore the need for an efficient typing system. Typing SCC mec cassettes in CoNS strains is crucial to continuously updating databases and developing a unified classification system.