Emergence of virulent methicillin-resistant Staphylococcus aureus strains carrying Panton-Valentine leucocidin genes in The Netherlands

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) strains carrying the Panton-Valentine leucocidin (PVL) genes have been reported worldwide and are a serious threat to public health. The PVL genes encode a highly potent toxin which is involved in severe skin infections and necrotizing pneumonia, even in previously healthy individuals. We assessed the prevalence of PVL-positive MRSA in The Netherlands for two periods of time: (i) 1987 through 1995 and (ii) 2000 and 2002, and determined their characteristics by using multilocus sequence typing and staphylococcal chromosome cassette (SCCmec) typing. It was found that up to 15% of all MRSA isolates detected in The Netherlands harbored the PVL genes. Most PVL-positive MRSA isolates were obtained from severe soft tissue infections in relatively young individuals. The first PVL-positive MRSA described in The Netherlands, isolated in 1988, was a single-locus variant of the "Berlin" epidemic MRSA clone. The 20 PVL-positive MRSA isolates studied in 2000 and 2002 consisted of five different sequence types (STs) that belonged to four clonal complexes. One of the STs, ST80, is considered to be a widespread European clone and was the most predominant ST (60%) in this study, while ST37 had never been found to be associated with PVL-positive MRSA. Most isolates harbored SCCmec type IV, a supposed marker for community-acquired MRSA. The number and type of virulence-associated genes varied among the different STs.

FIG. 1.

Population snapshot of S. aureus. The genetic relationships of the entire S. aureus database, including the five PVL-positive MRSA STs described in this study, are presented using a single eBURST diagram. The numbers represent STs and are indicated by black solid circles. The area of each circle corresponds to the abundance of the isolates of the ST in the input data. Presumed primary and secondary founders of clonal complexes are indicated in blue and yellow, respectively, while solid lines represent radial links from primary founders to each of its SLVs, which share identical alleles at 6 of the 7 loci, e.g., ST37 is an SLV of the primary founder ST30. The STs representing the PVL-positive MRSA isolates are marked by a red circle. Additional information about the eBURST algorithm can be found at www.mlst.net.