New methicillin-resistant Staphylococcus aureus (MRSA) clones, carrying type IV staphylococcal cassette chromosome mec (SCCmec), were identified in community-acquired MRSA strains in the United States and Australia. These clones multiplied faster than health-care-associated MRSA (H-MRSA) and were less resistant to non-beta-lactam antibiotics. They originated from more diverse S. aureus populations than H-MRSA strains. MRSA, once primarily a hospital pathogen, is now spreading in the community. However, the origin of community-acquired MRSA (C-MRSA) is unclear. Most H-MRSA strains carry one of three SCCmec types, but a novel SCCmec type IV was found in C-MRSA strains. This suggests C-MRSA may have a distinct origin from H-MRSA. Analysis of 23 C-MRSA strains and 12 Australian MRSA strains (NORSA) showed that C-MRSA/NORSA strains were more susceptible to non-beta-lactam antibiotics than H-MRSA. They exhibited a heterogeneous methicillin resistance phenotype, confirmed by population analysis. C-MRSA strains grew faster than H-MRSA, which may aid their colonization in the community. Genotyping revealed that C-MRSA/NORSA strains belonged to diverse clonal complexes, including CC1, which contains internationally dominant C-MRSA strains. These strains were distinct from H-MRSA strains. SCCmec typing showed that most C-MRSA/NORSA strains carried type IV SCCmec, while a few had a novel SCCmec with a class C2 mec gene complex. Type IV SCCmec is smaller and lacks antibiotic resistance genes other than mecA, which aligns with the non-multiresistant nature of C-MRSA/NORSA. This may reduce the fitness cost for H-MRSA strains with larger, more complex SCCmecs. The study highlights the emergence of new MRSA clones in the community, distinct from major H-MRSA clones. SCCmec and MLST typing are crucial for distinguishing C-MRSA from H-MRSA. The findings suggest that C-MRSA strains have evolved from diverse S. aureus populations and are spreading in the community due to their growth advantages.New methicillin-resistant Staphylococcus aureus (MRSA) clones, carrying type IV staphylococcal cassette chromosome mec (SCCmec), were identified in community-acquired MRSA strains in the United States and Australia. These clones multiplied faster than health-care-associated MRSA (H-MRSA) and were less resistant to non-beta-lactam antibiotics. They originated from more diverse S. aureus populations than H-MRSA strains. MRSA, once primarily a hospital pathogen, is now spreading in the community. However, the origin of community-acquired MRSA (C-MRSA) is unclear. Most H-MRSA strains carry one of three SCCmec types, but a novel SCCmec type IV was found in C-MRSA strains. This suggests C-MRSA may have a distinct origin from H-MRSA. Analysis of 23 C-MRSA strains and 12 Australian MRSA strains (NORSA) showed that C-MRSA/NORSA strains were more susceptible to non-beta-lactam antibiotics than H-MRSA. They exhibited a heterogeneous methicillin resistance phenotype, confirmed by population analysis. C-MRSA strains grew faster than H-MRSA, which may aid their colonization in the community. Genotyping revealed that C-MRSA/NORSA strains belonged to diverse clonal complexes, including CC1, which contains internationally dominant C-MRSA strains. These strains were distinct from H-MRSA strains. SCCmec typing showed that most C-MRSA/NORSA strains carried type IV SCCmec, while a few had a novel SCCmec with a class C2 mec gene complex. Type IV SCCmec is smaller and lacks antibiotic resistance genes other than mecA, which aligns with the non-multiresistant nature of C-MRSA/NORSA. This may reduce the fitness cost for H-MRSA strains with larger, more complex SCCmecs. The study highlights the emergence of new MRSA clones in the community, distinct from major H-MRSA clones. SCCmec and MLST typing are crucial for distinguishing C-MRSA from H-MRSA. The findings suggest that C-MRSA strains have evolved from diverse S. aureus populations and are spreading in the community due to their growth advantages.