Comparative genomics of community-associated methicillin-resistant Staphylococcus aureus shows the emergence of ST8-USA300 clone in Geneva, Switzerland.

Von Dach E1, Diene SM2, Fankhauser C1, Schrenzel J2, Harbarth S1, François P3.

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Abstract

BACKGROUND:

Previous investigations of community-associated (CA)-MRSA isolates have revealed a wide diversity of genetic backgrounds with only sporadic occurrence of ST8-USA300 in Geneva. We conducted an epidemiologic and molecular analysis to identify the origin of a sudden increase of ST8 PVL-positive isolates in Geneva during the year 2013.

METHODS:

Based on prospective CA-MRSA surveillance we collected isolates from colonized and infected cases with ST8-USA300 and compared them with non-ST8 CA-MRSA cases. Whole-genome sequencing (WGS) was performed for each isolate of this collection and discriminating molecular features were linked to patient data.

RESULTS:

In 2013, 22 isolates with ST8-USA300 profile were identified among 46 cases of CA-MRSA. WGS revealed two groups of strains that differed by the type of the SCCmec IV element encoded and whether they harbored an ACME locus. ACME-negative strains were mainly isolated from patients traveling in or originating from South America. SNP positions in isolate groups were used to infer their common ancestor, determine their geographical origin and trace their relatedness.

CONCLUSIONS:

WGS allowed the identification of transmission events and revealed that the increased prevalence of USA300 CA-MRSA isolates resulted from multiple importation events from the Americas but not from local clonal expansion of a successful clone.