Emergence of ST8-USA300 and ST8-USA300-Latin American variant: a changing landscape of community-associated methicillin-resistant Staphylococcus aureus in Chile.

Staphylococcus aureus is a versatile pathogen capable of causing various infections. Since the 1960s, the emergence of methicillin-resistant S. aureus (MRSA) has posed a significant challenge due to its antibiotic resistance. Among these, community-associated MRSA (CA-MRSA) emerged in the 1990s, which traditionally harbors the mecA gene and the Panton-Valentine leukocidin, affecting individuals without traditional risk factors. In this study, we aimed to describe the genetic and phenotypic characteristics of 54 CA-MRSA isolates circulating in Chile, collected between 2007 and 2023 from various healthcare centers across the country. All strains carried mecA, with SCCmec IVc being the most prevalent (67%). The predominant clone was USA300-Latin American variant (USA300-LV) (ST8-SCCmec IVc-COMER+) 43%, followed by USA300 (ST8-SCCmec IVa-ACME+) 15%, ST30-SCCmec IVc (15%), and ST5-SCCmec IVa (9%). All isolates were resistant to cefoxitin, and some exhibited additional resistance to erythromycin (18%), clindamycin (2%), and tetracycline (2%). Further studies on the molecular epidemiology of CA-MRSA in Chile should be performed, as our results evidenced the clonal nature and evolution of CA-MRSA in Chile, where the circulation of the ST8-USA300 and ST8-USA300-LV lineages in the community represents a serious threat for national public health.

Importance: The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) poses a significant public health threat. Unlike hospital-associated strains, CA-MRSA affects healthy individuals outside healthcare settings, often resulting in severe infections. The World Health Organization has designated MRSA as a priority pathogen due to its association with life-threatening infections worldwide. The increasing prevalence of CA-MRSA strains, particularly those resistant to multiple antibiotics, further complicates treatment efforts. Our findings highlight the predominance of the ST8-USA300 and ST8-USA300-Latin American variant clones in Chile, indicating the ongoing evolution of CA-MRSA in the region and suggesting the potential establishment of these clones within the community. Monitoring the spread and genetic diversity of these strains is essential for developing targeted interventions and informing public health strategies to control this pathogen and mitigate its impact on national health.