Virulent MRSA strains containing the Panton Valentine Leukocidin
gene in the Netherlands
Methicillin resistant Staphylococcus aureus
strains possessing the Panton Valentine Leukocidin (PVL) gene have been detected
in the Netherlands recently. The PVL gene encodes a highly potent toxin, which
is involved in severe skin infections and necrotising pneumonia. PVL positive
MRSA strains have also been noted in France (in healthy individuals; mean
age 14 years), in the United States (for example, in the Los Angeles gay community,
and in a large prison), and in Scotland (small outbreaks of skin abscesses
in healthcare staff. The Scottish MRSA reference laboratory is now routinely
screening both methicillin susceptible S. aureus
(MSSA) and MRSA
for the PVL gene). It has been suggested that the PVL MRSA is acquired in
the community (1-3).
The PVL gene was detected by polymerase chain reaction (PCR) (1) in approximately
10% of all MRSA isolates sent to the Dutch institute of Public Health and
the Environment (RIVM) national surveillance programme in the period 2000-2003.
Molecular subtyping by pulsed field gel electrophoresis (PFGE) on the Dutch
strains has shown a predominant clone, PFGE cluster 28. Although this clone
is known to be epidemic in the Netherlands, it has not caused large outbreaks
so far. The PFGE pattern of cluster 28 appears to be identical to the pattern
of the French PVL MRSA clone.
Identical PVL MRSA isolates (PFGE cluster 206) were found recently in two
Dutch HIV positive homosexual men. It is not yet known whether there is
a link with the PVL MRSA strains isolated from men who have sex with men
in the US.
About 90% of the PVL positive MRSA isolates in the Netherlands have been
obtained from soft tissue infections and (deep) purulent wound infections,
compared with 30% for PVL negative MRSA isolates. This significant increase
in the seriousness of infections caused by PVL MRSA is a finding shared
by the French group (1). The predominant Dutch clone (cluster 28) has so
far been shown to be 100% resistant to fusidic acid, neomycin, and tetracycline.
When testing all the PVL strains (cluster 28 plus others) the resistance
percentages are approximately 60, 70, and 70, respectively. The cluster
28 clone in particular has a characteristic antibiotic resistance profile,
which can be of use in the clinical laboratory.
Further studies will be performed in order to gain more insight into the
microbiological and epidemiological background of these virulent MRSA strains.
The combination of the PVL gene (virulence) and MecA gene (resistance)
and proven epidemicity (cluster 28) makes this a well adapted pathogen,
which can have severe implications, especially if further resistance markers