High genetic diversity among community-associated Staphylococcus aureus in Europe: results from a multicenter study

Abstract

Background: Several studies have addressed the epidemiology of community-associated Staphylococcus aureus (CA-SA) in Europe; nonetheless, a comprehensive perspective remains unclear. In this study, we aimed to describe the population structure of CA-SA and to shed light on the origin of methicillin-resistant S. aureus (MRSA) in this continent.

Methods and findings: A total of 568 colonization and infection isolates, comprising both MRSA and methicillin-susceptible S. aureus (MSSA), were recovered in 16 European countries, from community and community-onset infections. The genetic background of isolates was characterized by molecular typing techniques (spa typing, pulsed-field gel electrophoresis and multilocus sequence typing) and the presence of PVL and ACME was tested by PCR. MRSA were further characterized by SCCmec typing. We found that 59% of all isolates were associated with community-associated clones. Most MRSA were related with USA300 (ST8-IVa and variants) (40%), followed by the European clone (ST80-IVc and derivatives) (28%) and the Taiwan clone (ST59-IVa and related clonal types) (15%). A total of 83% of MRSA carried Panton-Valentine leukocidin (PVL) and 14% carried the arginine catabolic mobile element (ACME). Surprisingly, we found a high genetic diversity among MRSA clonal types (ST-SCCmec), Simpson's index of diversity = 0.852 (0.788-0.916). Specifically, about half of the isolates carried novel associations between genetic background and SCCmec. Analysis by BURP showed that some CA-MSSA and CA-MRSA isolates were highly related, suggesting a probable local acquisition/loss of SCCmec.

Conclusions: Our results imply that CA-MRSA origin, epidemiology and population structure in Europe is very dissimilar from that of USA.

Figure 1. Prevalence of MRSA and MSSA community-associated clones in Europe.

Distribution of the most prevalent MRSA and MSSA community-associated epidemic and related clones in 16 of the most populous European countries. Each color represents a different clone and related clonal lineages. A –MRSA; B –MSSA.

Figure 2. Analysis of spa typing data obtained for MRSA and MSSA isolates.

spa typing data from isolates belonging to epidemic and related CA-MRSA clones and sporadic isolates collected in the community and community-onset settings was analyzed by BURP (http://spaserver.ridom.de/, StaphType software v. 1.5, Ridom GmbH, Würzburg, Germany). Each spa type identified is depicted with circles. Related spa types are connected with a black line; resultant clonal complexes are depicted inside orange boxes. The predicted founder of each clonal complex is indicated in blue and in a larger circle. The size of the circles is proportional to the frequency of the spa type in the population. Each clonal complex (CC) is defined by the predicted founder spa type or by the spa types it contains. A –MRSA; B – MSSA.